Chapter 54. Pemphigus

The term pemphigus refers to a group of autoimmune blistering diseases of skin and mucous membranes that are characterized histologically by intraepidermal blisters due to acantholysis (i.e., separation of epidermal cells from each other) and immunopathologically by in vivo bound and circulating immunoglobulin (Ig) directed against the cell surface of keratinocytes. The nosology of this group of diseases is outlined in Box 54-1. Essentially, pemphigus can be divided into four major types: (1) vulgaris, (2) foliaceus, (3) paraneoplastic (see Chapter 55), and (4) IgA pemphigus (see Chapter 54). In pemphigus vulgaris (PV), the blister occurs in the deeper part of the epidermis, just above the basal layer, and in pemphigus foliaceus (PF), also called superficial pemphigus, the blister is in the granular layer.

The history of the discovery of pemphigus, and its various forms, is covered in Walter Lever's classic monograph Pemphigus and Pemphigoid.1 Both PV and PF display a spectrum of disease. Various points along these spectra have been given unique names, but because the presentation of these diseases is fluid, patients’ disease usually crosses these artificial designations over time. Thus, patients with PV may present with more localized disease, one form of which is called pemphigus vegetans of Hallopeau. This may become slightly more extensive and may merge into pemphigus vegetans of Neumann. Finally, with more severe disease, full-blown PV may appear. Similarly, patients with PF may present with more localized disease, represented by pemphigus erythematosus. However, these patients often go on to more widespread PF.

The discovery by Ernst Beutner and Robert Jordon in 1964 of circulating antibodies against the cell surface of keratinocytes in the sera of patients with PV pioneered our understanding that PV is a tissue-specific autoimmune disease of skin and mucosa.2 Ultimately, their work led the way to the discoveries of autoantibodies in other autoimmune bullous diseases of the skin.

Incidence and Prevalence

A few prospective and several retrospective surveys of patients with pemphigus clearly indicate that the epidemiology of pemphigus is dependent on both the area in the world that is studied as well as the ethnic population in that area.3–10 PV is more common in Jews and probably in people of Mediterranean descent and from the Middle East. This same ethnic predominance does not exist for PF. Therefore, in areas where the Jewish, Middle Eastern, and Mediterranean population predominates, the ratio of PV to PF cases tends to be higher. For example, in New York, Los Angeles, and Croatia, the ratio of PV to PF cases is approximately 5:1; in Iran the ratio is 12:1; whereas in Singapore it is 2:1; and in Finland, it is only 0.5:1. Similarly, the incidence of pemphigus varies by region. In Jerusalem, the incidence of PV has been estimated to be 1.6 per 100,000 people per year and in Iran approximately 10.0 per 100,000 people per year. Elsewhere in Europe, the incidences are lower, ranging from a high of 0.7 PV cases per 100,000 person years in the United Kingdom to tenfold less, 0.5–1.0 per million person years, in Finland, France, Germany, and Switzerland.

The prevalence and incidence of PF are also very dependent on its location, as best exemplified by the finding of endemic foci of PF in Brazil, Colombia, and Tunisia. The first recognition of endemic PF was in Brazil and is called fogo selvagem, which means “wild fire” in Portuguese. It is a disease that is clinically, histologically, and immunopathologically the same as sporadic PF in any individual patient, but its epidemiology is unique.11,12 Fogo selvagem is endemic in the rural areas of Brazil, especially along inland riverbeds. The geographic distribution of disease clustering is similar to that of a black fly, Simulium nigrimanum, thought by natives to be a vector of this disease. A study of potential environmental risk factors has also implicated the bite of this black fly, showing it to be significantly more frequent among those with the disease compared to an age-, sex-, and occupation-matched control population with unrelated dermatoses.13 The prevalence on some well-studied Indian reservations in rural Brazil can be as high as 3.4%, with the incidence up to 0.8–4.0 new cases per 1,000 people per year.12,14 On the reservation in Limao Verde, up to 55% of unaffected individuals have a low-level IgG1 antibody response against desmoglein 1, the PF autoantigen, which becomes an IgG4 response of higher titer against a more pathogenic epitope in disease.12 These results suggest that some environmental agent (e.g., insects or other infectious disease agent) may trigger a low-level autoantibody response that becomes pathogenic by intramolecular epitope spreading in genetically susceptible individuals. With this theory in mind, it is interesting that 40%–80% of patients from Brazil with the insect-borne diseases onchocerciasis, leishmania, and Chagas disease have low-level antidesmoglein 1 antibodies, but patients with other infectious diseases from Brazil rarely have such antibodies.15

Fogo selvagem occurs often in children and young adults, unlike sporadic PF, which is a disease of mostly middle-aged and older patients. Also unlike PF, fogo selvagem occurs not infrequently in genetically related family members, although it is not contagious. This fact probably implies a common exposure, as well as susceptibility. There is no known racial or ethnic predominance, and anyone moving into an endemic area may be susceptible to disease. Again supporting the presence of an environmental trigger, the development of the rural endemic areas of Brazil decreased the incidence of disease. Certainly, this fascinating disease holds clues to understanding how this autoimmune response is triggered.

Sex Ratio

The sex ratio of pemphigus cases is difficult to estimate accurately due to the overall low incidence. Larger epidemiologic studies (i.e., those identifying greater than 100 cases) have shown that the sex ratio of pemphigus in women versus men ranges from 1.33 or 2.25 to 1.7,9,16–20 Notable exceptions are the predominance of women (4:1) in an endemic focus of PF in Tunisia,6 and a predominance of men (19:1) in an endemic focus of PF in Colombia.21

Age of Onset

The average age of disease onset also varies by region. In Turkey, Saudi Arabia, Tunisia, and Iran, the mean age of onset is approximately 40 years.6,16,18,22 Studies in the United States and elsewhere in Europe demonstrate an average age of onset between 50 and 70 years.5,6,9,10,17,19,23,24,25 Pemphigus rarely occurs in children,26 except in regions of endemic disease.

The discovery of pemphigus as an organ-specific, autoantibody-mediated disease of desmosomes highlights the synergy between clinical care and basic science research. The development of light microscopy and electron microscopy allowed dermatologists to identify the morphology and immunopathology of disease. Patient serum IgG served as a key reagent to help identify both the PF and PV antigens.27–29 The cloning and characterization of the pemphigus antigens have subsequently led to the development of enzyme-linked immunosorbent assay (ELISA) tests to improve the sensitivity and specificity of disease diagnosis, and continued studies on pemphigus pathophysiology aim to develop safer and effective therapies for these potentially fatal diseases.

Pemphigus Autoantigens

Pemphigus antigens are desmogleins, transmembrane glycoproteins of desmosomes (cell-to-cell adhesion structures, reviewed in Chapter 53).30,31 Desmogleins are part of the cadherin superfamily of calcium-dependent cell adhesion molecules. The original members of this family (e.g., E-cadherin) demonstrate homophilic adhesive interactions (binding between like molecules). Desmogleins similarly demonstrate homophilic binding but can also participate in heterophilic adhesion by binding desmocollins, the other major transmembrane glycoprotein of desmosomes.32,33

The PF antigen (as well as the fogo selvagem antigen) is desmoglein 1, a 160-kDa protein.27,28,34 The PV antigen is desmoglein 3, a 130-kDa protein that is 64% similar and 46% identical in amino acid sequence to desmoglein 1.29 All patients with PV have antidesmoglein 3 antibodies, and some of these patients also have antidesmoglein 1 antibodies.35,36 Patients with mucosal-dominant PV tend to have only antidesmoglein 3 antibodies, whereas those with mucocutaneous disease usually have both antidesmoglein 3 and antidesmoglein 1 antibodies.37–39 PF patients typically have antibodies against only desmoglein 1.

Several lines of evidence indicate that antidesmoglein 1 and 3 antibodies in pemphigus patients directly cause blisters and hence are the etiologic agents of disease. Passive transfer of PV or PF IgG to neonatal mice or human skin causes blisters that clinically and histologically mimic the corresponding type of pemphigus in patients.40–42 The antidesmoglein antibodies are responsible for blister formation in the passive transfer model, since affinity purified antidesmoglein 1 and 3 autoantibodies cause PF and PV blisters, respectively, and adsorption of desmoglein-reactive autoantibodies from PF or PV IgG abrogates disease.43–46 Similar passive transfer “experiments” have been described in humans, where mothers with even mild PV can pass IgG autoantibodies to the fetus, causing blistering oral and skin disease that resolves by approximately 6 months, concurrent with the disappearance of maternal IgG from the circulation.47

Desmoglein 4, which is expressed in the developing hair cortex and the superficial epidermis, is a target of some pemphigus antibodies.48 However, the antidesmoglein 4 antibodies in mucocutaneous PV and in PF have been shown to be a result of cross-reactivity from desmoglein 1 autoantibodies, and the desmoglein 4 reactivity has not been shown to be necessary or sufficient for acantholysis.49 Other cell surface molecules such as acetylcholine receptors and E-cadherin have also been identified as immunologic targets of pemphigus autoantibodies, although their direct involvement in the pathophysiology of pemphigus is similarly unclear.50,51

Electron Microscopy

Pathophysiology of Acantholysis

Unlike many other autoantibody-mediated diseases, such as pemphigoid and epidermolysis bullosa acquisita, in which the constant region of the antibody is required for blister formation to activate complement or bind antibody receptors on inflammatory cells, in pemphigus the variable region of the antibody is sufficient to cause blisters in neonatal mice or human skin.42,60–62 For this reason a significant amount of research on disease pathophysiology has focused on the epitopes bound by pathogenic autoantibodies, as these regions are likely critical for maintaining desmosomal cell adhesion.

Epitope mapping studies have shown that pathogenic PV and PF autoantibodies bind calcium-sensitive, conformational epitopes in the amino-terminal extracellular domains of desmogleins, whereas nonpathogenic antibodies tend to bind more membrane proximal extracellular domains.63–66 The amino-terminal domains bound by pathogenic autoantibodies are the same domains that are predicted to form the key molecular interactions for desmoglein intercellular adhesion, based on studies of cadherin ultrastructure.67,68 This evidence is the primary basis for the “steric hindrance” hypothesis, which proposes that pathogenic antibodies directly interfere with desmoglein adhesive interactions, causing acantholysis.

Studies on cultured keratinocytes have indicated that loss of intercellular adhesion by pathogenic autoantibodies leads to internalization and degradation of desmogleins,69–72 indicating that pemphigus antibody binding leads to loss of desmoglein function. If this is the case, then other model systems with loss of desmoglein function should mimic pemphigus. Indeed, mice genetically deficient for desmoglein 3 demonstrate suprabasal blisters in the oral mucosa histologically identical to PV patients.73 Additionally, cleavage of desmoglein 1 by staphylococcal exfoliative toxin (in bullous impetigo or staphylococcal scalded skin syndrome) causes blisters histologically identical to those seen in PF patients.74

If inactivation of desmoglein isoforms results in blistering, then why do blisters in PV and PF have specific tissue localizations that do not necessarily correlate with the sites at which the antibodies bind by immunofluorescence? In PF, for example, the antidesmoglein 1 antibodies bind throughout the epidermis and mucous membranes,75 yet blisters occur only in the superficial epidermis. This apparent paradox can be explained by desmoglein compensation, as outlined in Fig. 54-1. The concept of desmoglein compensation originates in the assumption that autoantibodies against one desmoglein isoform inactivate only that isoform and that another isoform coexpressed in the same area can compensate in adhesion.76–78 Desmoglein compensation explains why neonatal PF is so unusual, because even though the maternal antidesmoglein 1 antibodies cross the placenta, in neonatal skin, but not in adult skin, desmoglein 3 is coexpressed with desmoglein 1 in the superficial epidermis, thereby providing protection against the loss of desmoglein 1-based adhesion.77,79 Desmoglein compensation also offers an explanation for the differing sites of blister formation in PV and PF, both in regard to the histology (i.e., suprabasal or superficial), as well as the areas of involvement (mucosa and/or skin.)

In potential challenge to the steric hindrance hypothesis, several studies have suggested that modulation of cell signaling pathways can prevent blister formation after passive transfer of pemphigus IgG in the neonatal mouse model, including p38 mitogen activated protein kinase (MAPK) and ρ GTPases, among others.80–82 Whether signaling is upstream or downstream of the loss of intercellular adhesion is controversial. Nevertheless, the current general consensus is that desmosomal adhesion is a dynamic process that is perturbed by pemphigus autoantibodies. Therefore, therapies that aim to strengthen keratinocyte adhesion by modulation of signaling pathways may have a beneficial effect on pemphigus, regardless of whether cell signaling is a primary pathologic cause of disease.

Genetic Restriction of the Pemphigus Immune Response

Compared to a matched population, patients with PV have a markedly increased frequency of certain class II major histocompatibility complex (MHC) antigens. Among Ashkenazi Jews with PV, the serologically defined HLA-DR4 haplotype is predominant, whereas in other ethnic groups with PV, the DQ1 allele is more common.83 However, the association with disease susceptibility becomes even more striking in an analysis of these MHC alleles at a genetic level. Patients with the DR4 serotype almost all have the unusual allele DRB1*0402, and patients with the DQ1 serotype almost all have the rare allele DQB1*0503. Similar, but less restricted, HLA-DR alleles are associated with PF.84 The protein chains encoded by these PV MHC II alleles vary from those found in HLA-DR4 and DQ1 controls without disease by only a few amino acids.

MHC class II alleles encode cell surface molecules that are necessary for antigen presentation to the immune system; therefore, it is hypothesized that PV-associated MHC class II molecules allow presentation of desmoglein 3 peptides to T cells.85 Consistent with this hypothesis, certain peptides from desmoglein 3, predicted to fit into the DRB1*0402 peptide-binding pocket, were found to stimulate T cells from patients.86

Other studies have confirmed that the immune response in pemphigus is restricted to certain desmoglein peptides and MHC class II alleles.87–89 An unexpected observation was that T cells of normal people with the DRB1*0402 or DQB1*0503 respond just as well as those of pemphigus patients to the same desmoglein 3 peptides,85,90 indicating that T-cell reactivity to desmoglein 3 peptides is not sufficient for disease onset. The factor that may determine who gets pemphigus and who does not has been proposed to be the presence of regulatory T cells that can suppress the autoimmune response in those who do not.91

Cloning of antidesmoglein antibodies from PV and PF patients has indicated a marked restriction of antibody gene usage by the antidesmoglein antibodies, most notably for the heavy chain variable region.61,62,92 These studies also show that pathogenic antibodies from different patients bind at or near common epitopes on desmogleins and may share common idiotypes. In comparison to the restricted B-cell antibody variable region gene usage, there is more heterogeneity of the T-cell receptor variable gene usage in pemphigus patients.90,93 If specific antibody or T-cell receptor gene usage patterns are found to be shared among multiple pemphigus patients, these may serve as clinical markers for targeting disease-specific immune cell populations in pemphigus patients.

Pemphigus Vulgaris

Cutaneous Lesions

The skin lesions in PV can be pruritic or painful. Exposure to ultraviolet radiation may exacerbate disease activity.94,95 The primary lesion of PV is a flaccid blister, which may occur anywhere on the skin surface, but typically not the palms and soles (Fig. 54-2). Usually, the blister arises on normal-appearing skin, but it may develop on erythematous skin. Because PV blisters are fragile, the most common skin lesions observed in patients are erosions resulting from broken blisters. These erosions are often quite large, as they have a tendency to spread at their periphery (Fig. 54-3).

A characteristic finding in pemphigus patients is that erosions can be extended into visibly normal skin by pulling the remnant of the blister wall or rubbing at the periphery of active lesions; additionally, erosions can be induced in normal-appearing skin distant from active lesions by pressure or mechanical shear force. This phenomenon is known as the Nikolsky sign.96 This sign helps differentiate pemphigus from other blistering diseases of the skin such as pemphigoid (Box 54-1); however, similar findings can also be elicited in staphylococcal scalded skin syndrome, Stevens–Johnson syndrome, and toxic epidermal necrolysis.

Vegetating Lesions

In certain patients, erosions have a tendency to develop excessive granulation tissue and crusting, referred to as vegetating lesions (Fig. 54-4). This type of lesion tends to occur more frequently in intertriginous areas, in the scalp, or on the face (see Fig. 54-4A). Historically, patients presenting with vegetating lesions have been split out into different disease designations: pemphigus vegetans of Hallopeau and pemphigus vegetans of Neumann. However, the subsequent analysis of vegetating skin lesions by histology and immunofluorescence suggests that these cases are simply clinical variants of PV.1,97 In the Hallopeau variant, vegetating and often pustular lesions are present from the outset of disease, are not preceded by bullae, and favor flexural regions (see Fig. 54-4B). Generally, the prognosis for these patients is thought to be better, with milder disease and a higher chance of remission compared to typical PV patients.98 In patients with the Neumann variant, ordinary PV erosions heal with papillomatous formations, with prognosis related to the extent of disease activity. The vegetating type of response may also appear in certain lesions that tend to be resistant to therapy and remain for long periods of time in one place. Thus, vegetating lesions seem to be one reactive pattern of the skin to the autoimmune insult of PV.

Mucous Membrane Lesions

The mucous membranes most often affected by PV are those of the oropharyngeal cavity (see Fig. 54-2B). As with cutaneous lesions, intact blisters are rare. Oropharyngeal erosions can be so painful that the patient is unable to eat or drink. The inability to eat or drink adequately may require inpatient hospitalization for disease control and intravenous fluid and nutrient repletion.

In the majority of patients, painful mucous membrane erosions are the presenting sign of PV and may be the only sign for an average of 5 months before skin lesions develop.3 However, the presenting symptoms may vary; in a study from Croatia, painful oral lesions were the presenting symptom in 32% of patients.20 Most of these patients progressed to a more generalized eruption in 5 months to 1 year; however, some had oral lesions for more than 5 years before generalization. On the other hand, in Tehran, 62% of patients presented with oral lesions only.7 Skin involvement without mucous membrane involvement in PV is less common, accounting in one study for 11% of PV cases.99

Gastrointestinal tract involvement with PV has been described in the esophagus, stomach, duodenum, and anus, although only biopsies of the esophagus have been proven to be due to suprabasal acantholysis.7,100,101 Involvement of other mucous membranes can also occur, including the vulvovaginal, nasal, laryngeal, and conjunctival mucosa.102–106 In women, cervicovaginal lesions may be found in up to 51% of patients with active disease but these lesions may be asymptomatic. Even without obvious lesions, Pap smears may be positive in women with pemphigus and the acantholytic cells may be misinterpreted as indicative of cervical dysplasia.107,108 There are rare case reports on corneal erosions in PV patients, but no histologic confirmation of acantholysis.109

Pemphigus Foliaceus

Cutaneous Lesions

The characteristic clinical lesions of PF are scaly, crusted erosions, often on an erythematous base. In more localized and early disease, these lesions are usually well demarcated and scattered in a seborrheic distribution, including the face, scalp, and upper trunk (Fig. 54-5A). The primary lesions of small flaccid blisters are typically not found. Disease may stay localized for years, or it may rapidly progress to generalized involvement, resulting in an exfoliative erythroderma (Fig. 54-5B). Like PV, PF may be exacerbated by ultraviolet radiation.95,110,111 Patients with PF often complain of pain and burning in the skin lesions. In contrast to patients with PV, those with PF very rarely, if ever, have mucous membrane involvement, even with widespread disease.

The colloquial term for Brazilian endemic pemphigus, fogo selvagem (Portuguese for “wild fire”), takes into account many of the clinical aspects of this disease: the burning feeling of the skin, the exacerbation of disease by the sun, and the crusted lesions that make the patients appear as if they had been burned.

Pemphigus Erythematosus

In 1926, Francis Senear and Barney Usher described eleven patients with features of a pemphigus–lupus erythematosus overlap (Senear–Usher syndrome).112 Over the next several decades, debate over whether these patients had lupus erythematosus, pemphigus, seborrheic dermatitis, or features of all three disorders continued, with Senear concluding that the disease is best considered a variant of pemphigus, termed pemphigus erythematosus.113 As these observations were made prior to the development of immunofluorescence testing for both pemphigus and lupus, the diagnosis was primarily based on the clinical presentation: crusted erosions in a seborrheic distribution, at times concurrent with more lupus-like discoid lesions with “carpet-tack” scale. Walter Lever noted that many patients initially categorized as pemphigus erythematosus went on to develop systemic lupus, or more widespread PF, or even PV, in some cases due to incorrect initial diagnosis. Therefore, rather than perpetuate the use of one term for different diseases, he proposed that pemphigus erythematosus be used to describe a localized form of PF with better prognosis.1 After the development of immunofluorescence and antinuclear antibody testing for pemphigus and lupus, it was discovered that pemphigus erythematosus patients demonstrate immunologic overlap features; by definition all demonstrate the cell surface staining pattern classic for pemphigus, approximately 30% have positive antinuclear antibody titers, and 80% have positive lupus band tests, although the latter test is only positive in 20%–40% of biopsies on nonsun-exposed skin.114 As most patients with pemphigus erythematosus do not develop systemic signs or symptoms of lupus, and some may progress from localized disease to generalized PF,115 the diagnosis of pemphigus erythematosus is largely one of historic, rather than clinical, significance.

Neonatal Pemphigus

Infants born to mothers with PV may display clinical, histologic, and immunopathologic signs of PV.47,116 The degree of involvement varies from none to severe enough to result in a stillbirth. If the infant survives, disease tends to remit as maternal antibody is catabolized. Mothers with PF may also transmit their autoantibodies to the fetus, but, as discussed in Section “Pathophysiology of Acantholysis,” neonatal PF occurs only rarely.117–119 Neonatal pemphigus should be distinguished from PV and PF that occur in childhood, which are similar to the autoimmune diseases seen in adults.120

Drug-Induced Pemphigus

Although there are sporadic case reports of pemphigus associated with the use of several different drugs, the association with penicillamine, and perhaps captopril, is the most significant.121 The prevalence of pemphigus in penicillamine users is estimated to be approximately 7%. PF (including pemphigus erythematosus) is more common than PV in these penicillamine-treated patients, although either may occur. The findings of direct and indirect immunofluorescence are positive in most of these patients. Three patients with drug-induced PF and one with drug-induced PV have been shown to have autoantibodies to the same molecules involved in sporadic pemphigus, namely, desmoglein 1 and desmoglein 3, respectively.122 Therefore, by immunofluorescence and immunochemical determinations, these patients with drug-induced pemphigus resemble those with sporadic disease.

Both penicillamine and captopril contain sulfhydryl groups that are postulated to interact with the sulfhydryl groups in desmoglein 1, 3, or both, thereby causing pemphigus either by directly interfering with these adhesion molecules or, more likely, by modifying them so that they become more antigenic. The use of these drugs may also lead to a more generalized dysregulation of the immune response, allowing production of other autoantibodies such as those resulting in myasthenia gravis. Most, but not all, patients with drug-induced pemphigus go into remission after they stop taking the offending drug.

Additionally, rare anecdotal reports have suggested the association of dietary intake and pemphigus, proposing the hypothesis that thiol-containing foods such as garlic, leeks, and onions may precipitate disease.123,124 Some patients may note that certain foods aggravate oral lesions, but it is unlikely that dietary intervention alone will remit disease in most patients.

Interestingly, anecdotal case reports have reported improvement of PV with cigarette smoking,125 as well as with the cholinergic agonists pyridostigmine, carbachol, and pilocarpine.126,127 Studies suggest that activation of cholinergic receptors may regulate signaling pathways modulated by PV IgG, thereby affecting cell adhesion.128 These results are intriguing given the clinical benefit of nicotine noted in other inflammatory diseases, such as ulcerative colitis.129

Associated Diseases

Myasthenia gravis, thymoma, or both have been associated with PV and PF.130 Approximately one-half of associated pemphigus cases are vulgaris; one-half, foliaceus or erythematosus. Most of these data, however, were reported before the recognition of paraneoplastic pemphigus as a distinct entity. Therefore, although thymoma may clearly be associated with PV and PF, it may also be associated with paraneoplastic pemphigus (see Chapter 55). Myasthenia gravis is a tissue-specific autoantibody-mediated disease leading to skeletal muscle weakness. Early disease usually affects facial muscles, leading to symptoms of dysarthria, dysphagia, ptosis, or diplopia. Disease may then progress to affect the larger muscles of the trunk and extremities, with potential fatal complications from respiratory muscle involvement. Thymoma, in contrast, is typically asymptomatic in adults. In children, thymomas are more likely to be symptomatic with cough, chest pain, superior vena cava syndrome, dysphagia, and/or hoarseness from localized tumor encroachment.

Myasthenia gravis would be best evaluated by a neurologist, who can complete a full neurologic examination and may test for the presence of serum acetylcholine receptor autoantibodies. The course of myasthenia gravis and pemphigus appear to be independent of each other. Likewise, thymic abnormalities may either precede or follow the onset of pemphigus. Thymic abnormalities include benign or malignant thymoma and thymic hyperplasia. Posteroanterior and lateral chest radiographs with or without computerized tomography follow-up can detect most thymomas. Irradiation of the thymus or thymectomy, although clearly beneficial for myasthenia gravis, may not improve the pemphigus disease activity. Although this association is reported in at least 30 cases, the finding of thymoma or myasthenia gravis in a patient with PV or PF is still unusual.

Diagnosis of pemphigus relies on skin biopsy of a fresh lesion for histology to determine the site of blister formation, as well as a confirmatory immunochemical study to document the presence of skin autoantibodies, either by direct immunofluorescence of perilesional skin, or indirect immunofluorescence or ELISA of patient serum.

Histology

The characteristic histopathologic finding in PV is a suprabasal blister with acantholysis (Fig. 54-6). Just above the basal cell layer, epidermal cells lose their normal cell-to-cell contacts and form a blister. Often, a few rounded up (acantholytic) keratinocytes are in the blister cavity. The basal cells stay attached to the basement membrane, but may lose the contact with their neighbors; as a result, they may appear to be a “row of tombstones,” symbolic of the potentially fatal prognosis of this disease. Usually, the upper epidermis (from one or two cell layers above the basal cells) remains intact, as these cells maintain their cell adhesion. Pemphigus vegetans shows not only suprabasilar acantholysis, but also papillomatosis of the dermal papillae and downward growth of epidermal stands into the dermis, with hyperkeratosis and scale-crust formation. In addition, pemphigus vegetans lesions may show intraepidermal abscesses composed of eosinophils and/or neutrophils.131 Early PV lesions may show eosinophilic spongiosis.132

The histopathology of early blisters in PF patients demonstrates acantholysis (loss of cell-to-cell contact) just below the stratum corneum and in the granular layer (Fig. 54-7A). The stratum corneum is often lost from the surface of these lesions. The deeper epidermis, below the granular layer, remains intact. Another frequent finding is subcorneal pustules, with neutrophils and acantholytic epidermal cells in the blister cavity (Fig. 54-7B). Histologic findings in PF are often indistinguishable from those seen in bullous impetigo/staphylococcal scalded skin syndrome, because blisters in these latter diseases also result from dysfunction of desmoglein 1, in these cases due to proteolytic cleavage by staphylococcal exfoliative toxins.31 Therefore, immunochemical studies are essential to confirm a diagnosis of PF, as these would be negative in staphylococcal-mediated skin blisters. The site of blister formation in pemphigus erythematosus is identical to PF. As in PV lesions, very early PF lesions may show eosinophilic spongiosis.132

Immunofluorescence

The hallmark of pemphigus is the finding of IgG autoantibodies against the cell surface of keratinocytes. These autoantibodies were first discovered in patients’ sera by indirect immunofluorescence techniques and soon thereafter were discovered by direct immunofluorescence of patients’ skin.133

Direct Immunofluorescence

Essentially all patients with active PV or PF have a positive finding on a direct immunofluorescence study, which tests for IgG bound to the cell surface of keratinocytes in perilesional skin (Fig. 54-8A).134 This is a nonquantitative test (either negative or positive). The diagnosis of pemphigus should be seriously questioned if the test result of direct immunofluorescence is negative. It is important that the biopsy for direct immunofluorescence be performed on normal-appearing perilesional skin, as the immune reactants can be difficult to detect in blistered inflamed epidermis (leading to a false negative result). In some cases of pemphigus erythematosus, IgG and C3 are deposited at the basement membrane zone of erythematous facial skin, in addition to the epidermal cell surface IgG, representing a positive lupus band test in addition to the typical pemphigus intercellular pattern.135

Indirect Immunofluorescence

Indirect immunofluorescence is performed by incubating serial dilutions of patients’ sera with epithelial substrates. It is reported as a semiquantitative titer (indicating the last dilution at which the serum demonstrates a positive cell surface staining pattern). The test is offered by most major national laboratories and can remain positive for weeks to months after healing of skin lesions, making it a good diagnostic test if a patient should present with no active skin lesions, for example, due to empiric treatment with prednisone by a referring physician. Depending on the substrate used for indirect immunofluorescence, more than 80% of patients with pemphigus have circulating antiepithelial cell surface IgG (Fig. 54-8B).136 The substrate used to detect pemphigus antibody binding in indirect immunofluorescence greatly influences the sensitivity of the test. In general, monkey esophagus is more sensitive for detecting PV antibodies, and guinea pig esophagus or normal human skin is a superior substrate for detecting PF antibodies. Patients with early localized disease and those in remission are most likely to have negative findings on an indirect immunofluorescence test; for these patients the increased sensitivity of ELISA may help in diagnosis (see below).

Patients with PV and PF usually display similar direct and indirect immunofluorescence findings with IgG on the cell surface of epidermal cells throughout the epidermis, despite the different autoantigen profiles in these two diseases. Therefore, it is usually not possible to differentiate the two diseases by the pattern of immunofluorescence. There is a positive, but imperfect, correlation between the titer of circulating anticell surface antibody and the disease activity in PV and in PF.137 Although this correlation may hold in general, and although patients in remission often show serologic remission with negative direct and indirect immunofluorescence findings,138,139 disease activity in individual patients does not necessarily correlate with indirect immunofluorescence titer. Therefore, in the day-to-day management of these patients, following disease activity is more important than following antibody titer.

Enzyme-Linked Immunosorbent Assay

For diagnosis of disease, antigen-specific ELISAs have been shown to be more sensitive and specific than immunofluorescence, and their titer correlates better than that of indirect immunofluorescence with disease activity.35,140 Additionally, ELISAs are easier to perform and less subjective than immunofluorescence, and may replace the latter as the preferred first diagnostic test for pemphigus, although currently some major national laboratories do not offer desmoglein ELISA. These assays use desmogleins 1 and 3 bound to plates, which are then incubated with patient sera and developed with antihuman IgG reagents (Fig. 54-9). As an advantage over indirect immunofluorescence, ELISAs can help differentiate between PV and PF due to the different autoantigen profiles in these two diseases.35,140,141,142 In most cases, ELISA is positive for desmoglein 3 (but not desmoglein 1) in mucosal PV, is positive for both desmogleins 3 and 1 in PV with both mucosal and significant skin involvement, and is positive for only desmoglein 1 in PF. PV has rarely evolved into PF, and vice versa, as determined by clinical, histologic, and immunochemical criteria.143–145 A small minority of PF patients may also demonstrate autoantibodies to desmoglein 3146; therefore, diagnosis should be made based on the clinical–serologic correlation. Additionally, some patients (e.g., those with bullous pemphigoid) may demonstrate a low level of antidesmoglein 3 autoantibodies,140 which are detectable due to the high sensitivity of the ELISA. Therefore, a result in the indeterminate range should be interpreted carefully, as this may represent a true positive or a false negative, the latter presumably due to formation of nonpathogenic bystander autoantibodies after epidermal damage. As with indirect immunofluorescence, the correlation of ELISA index value with disease activity is not perfect. In making treatment decisions, a negative result on desmoglein ELISA is more helpful than a positive result, as a patient with the former is more likely to achieve remission off immunosuppressives, whereas a patient with the latter may or may not. In other words, disease activity is the mainstay for determining treatment.

Before the advent of glucocorticoid therapy, PV was almost invariably fatal due to severe blistering of the skin and mucous membranes leading to malnutrition, dehydration, and sepsis. PF was fatal in approximately 60% of patients. PF was almost always fatal in elderly patients with concurrent medical problems; however, in other patients its prognosis, without therapy, was much better than PV.147,148

The systemic administration of glucocorticoids and the use of immunosuppressive therapy have dramatically improved the prognosis for patients with pemphigus; however, pemphigus is still a disease associated with a significant morbidity and mortality.149,150 In the United States, the annual mortality rate from pemphigus (age-adjusted to the standard population) is estimated to be 0.023 deaths per 100,000.151 A study in the United Kingdom showed that the risk of death in PV patients is 3.3 times greater than for controls.9 Infection is often the cause of death, and by causing the immunosuppression necessary in the treatment of active disease, therapy is frequently a contributing factor.152 With glucocorticoid and immunosuppressive therapy, the mortality (from disease or therapy) of PV patients followed from 4 to 10 years is approximately 10% or less, whereas that of PF is probably even less. In a study of 40 patients with PV, two patients (5%) died of sepsis and 17%, after an average of 18 months of therapy, went into a complete and long-lasting (>4 years, average, thought to be permanent) remission requiring no further therapy.153 Another 37% of patients achieved remission but relapsed at times after therapy was stopped; most of these also eventually achieved long-lasting remissions. The remainder of patients required continual therapy. In a group of 159 patients with PV from Croatia, only approximately 12% went into long-term remission after therapy with glucocorticoids and immunosuppressives, but most relapsed.20 In a study from Tehran of 1,206 pemphigus patients seen over 20 years, 6.2% of PV and 0.2% of PF patients died, mostly of septicemia; only 9.3% were in complete remission without therapy.7 In some small studies, higher percentages of patients were reported to go into complete remission (see below). With the advent of rituximab therapy, complete remission in pemphigus may become more common.

Despite the potentially fatal prognosis, there are currently no FDA-approved treatments. Approach to therapy of pemphigus varies widely, even among experts.154 It is generally agreed that PV, even if initially limited in extent, should be treated at its onset, because it will ultimately generalize and the prognosis without therapy is very poor. In addition, it is probably easier to control early disease than widespread disease, and mortality may be higher if therapy is delayed.155 Because PF may be localized for many years, and the prognosis without systemic therapy may be good, patients with this type of pemphigus do not necessarily require treatment with systemic therapy; the use of topical corticosteroids may suffice. When the disease is active and widespread, however, the therapy for PF is, in general, similar to that for PV.

Recently, a consensus statement on disease definitions and endpoints was proposed by an international committee of pemphigus experts.156 Additionally, clinical instruments have been developed for tracking disease activity.157,158 The standardization of disease definitions and activity scoring will facilitate future clinical trials for pemphigus.

Corticosteroids

The systemic administration of glucocorticoids, usually prednisone, is the mainstay of therapy for pemphigus. Before adjuvant immunosuppressive therapy was available, very high initial doses of prednisone (>2.0 mg/kg/day) were used for treatment, although such regimens have retrospectively been associated with significant morbidity and mortality from therapy.152,159,160 In many patients the disease can be brought under control with a 0.5–1.0 mg/kg/day single daily dose, especially if used in combination with adjunctive immunosuppressive therapy, which is thought to result in fewer complications and decreased mortality as compared to higher dose glucocorticoid regimens.161,162 For patients who do not initially respond or worsen, splitting the dose using a twice or three times daily schedule may achieve disease control. The full systemic dose of glucocorticoids has been defined in the consensus guidelines as 1.5 mg/kg/day of prednisone equivalent for 3 weeks. Therefore, patients whose total daily prednisone dose exceeds approximately 100 mg should be considered for adjunctive treatments, discussed below. Some experts still recommend controlling initial refractive disease with escalating doses of prednisone (increasing by 50% every 1 to 2 weeks until disease control or prohibitive side effects occur), with total daily doses as high as 240 mg.148,163

Once disease activity is controlled, tapering prednisone to as low a dose as possible should be the goal. Minimal therapy is defined as 10 mg daily of prednisone equivalent. Although there are no set guidelines, if disease activity can be fully controlled on minimal dose prednisone or lower, then glucocorticoid monotherapy may be feasible depending on the patient's other comorbidities and contraindications to alternative immunosuppressive agents. If patients have continued relapses with daily prednisone doses of 10 mg or higher, adjunctive immunosuppressive agents should be considered.

Interestingly, prednisone can control blistering within days, at a time when the autoantibody titer would be unchanged. A possible explanation is that prednisone may increase the synthesis of desmogleins or other cell adhesion molecules or change their posttranscriptional processing to prolong their half-life.164 If pemphigus IgG depletes desmosomes of desmogleins, then prednisone could counteract this effect.

Topical corticosteroids may be used as monotherapy in mild forms of disease, or as adjunctive therapy to help heal new lesions. Patients with mucosal disease may benefit from the use of glucocorticoid elixirs as a swish and spit or dental trays to help apply class I corticosteroid gels or ointments to the gingiva. Additionally, class I–IV corticosteroids can be used as topical therapy to help resolve new blisters, even in patients on systemic glucocorticoids.

Immunosuppressive Agents

When greater than minimal doses of glucocorticoids are required for disease control, or if there are contraindications to oral glucocorticoids, other immunosuppressive agents are used for pemphigus therapy. In many cases, treatment regimens often begin with an immunosuppressive agent and prednisone simultaneously. Prospective randomized studies have shown that immunosuppressive agents such as mycophenolate mofetil, azathioprine, and cyclophosphamide have a steroid-sparing effect; retrospective studies suggest decreased mortality with use of adjuvants plus steroids compared to steroids alone.147,165,166

Because patients may die from complications of therapy, it is important to monitor all patients closely for potential side effects, such as blood count, liver and kidney laboratory abnormalities, gastrointestinal ulcer disease, high blood pressure, diabetes, glaucoma, cataracts, osteoporosis, and infection. The decision to use immunosuppressive agents, particularly in young patients, must also take into account the potential incidence of malignancies that might be associated with the long-term use of these drugs, as well as the risks of infertility (for cyclophosphamide) and teratogenicity (for mycophenolate mofetil, azathioprine, and cyclophosphamide, which are all pregnancy category D).

Azathioprine

Azathioprine has historically been considered as a first-line immunosuppressive agent for pemphigus, with clinical remission rates of approximately 50% in retrospective studies.139,167 In a prospective randomized trial of high dose methylprednisolone (2.0 mg/kg/day) plus azathioprine (2.0 mg/kg/day), 72% of patients achieved clinical remission within a mean of 74 days, although 33% experienced significant adverse effects of therapy, including hyperglycemia, dizziness, abnormal liver enzyme tests, and infection.165

Azathioprine is a prodrug, which is converted to active mercaptopurine, thioguanine, and thioinosine metabolites, in part by thiopurine methyltransferase (TPMT), an enzyme whose levels can vary widely in the population. 89% of Caucasians demonstrate normal to high levels of TPMT, 11% are intermediate, and 0.3% are deficient for TPMT, the latter group representing those who do not tolerate azathioprine therapy.168 Additionally, 1%–2% of Caucasians may have “super high” levels of TPMT, which is correlated with both treatment resistance as well as increased hepatotoxicity from excessive metabolite production.169 Altogether, it is estimated that 5% of patients will be azathioprine intolerant, although the genotype–phenotype correlation is imperfect.170

In patients with normal TPMT levels, the consensus dosing regimen that defines treatment failure is 2.5 mg/kg/day for 12 weeks.156 From a practical standpoint however, not all laboratories offer TPMT testing. Additionally, since patients with normal levels of TPMT may also experience azathioprine toxicity, it is reasonable to start all patients at a lower dose (e.g., 50–100 mg daily) and titrate upward until clinical remission, the target dose of 2.5 mg/kg/day, or unacceptable side effects result. Frequent blood and liver monitoring should continue, particularly over the first 8–12 weeks when delayed toxicity from the accumulation of metabolites may emerge.

Mycophenolate Mofetil

Mycophenolate mofetil is also considered to be a first-line immunosuppressive agent for pemphigus. In 2006, the FDA granted orphan drug status to mycophenolate mofetil for the treatment of PV, thereby increasing the feasibility of a new drug approval. Typical doses range from 30–40 mg/kg/day dosed twice daily (2.0–3.0 g/day), although certain patients such as the elderly may achieve disease control with doses as low as 1.0 g/day.

In case series, mycophenolate mofetil has been shown to have a rapid effect in lowering pemphigus antibody titers and decreasing disease activity, even in patients whose disease is unresponsive to azathioprine.171,172 A prospective randomized trial comparing methyprednisolone (2.0 mg/kg/day) with azathioprine (2.0 mg/kg/day) or mycophenolate mofetil (2.0 g/day) in pemphigus patients showed 72% in the azathioprine group and 95% in the mycophenolate mofetil group went in clinical remission in a mean of 74 and 91 days, respectively.165 19% of patients experienced significant side effects of mycophenolate mofetil therapy, compared to 33% in the azathioprine group. None of these differences was statistically significant. Another prospective randomized study indicated that azathioprine was significantly more effective than mycophenolate mofetil as a steroid sparing agent, although this study compared a full dose of azathioprine (2.5 mg/kg/day) to a partial dose of mycophenolate mofetil (2.0 g/day).166 Caution with use of mycophenolate mofetil is warranted, as fatal infection and sepsis occurred in 2%–5% of transplant patients receiving mycophenolate mofetil, and increased risk of infection with or reactivation of cytomegalovirus, herpes zoster, atypical mycobacteria, tuberculosis, and John Cunningham (JC) virus (in progressive multifocal leukoencephalopathy) have been noted in postmarketing surveillance.173 Interestingly, mycophenolate mofetil may offer protection against Pneumocystis carinii infection.174

Cyclophosphamide

Cyclophosphamide, although more toxic than azathioprine or mycophenolate mofetil, is thought to be very effective in controlling severe disease, with one report of 19 of 23 patients with pemphigus achieving complete remission in a median time of 8.5 months.175 A variety of small case series have evaluated different cyclophosphamide regimens for pemphigus, including daily oral therapy (1.1–2.5 mg/kg/day), daily oral therapy (50 mg) with intermittent high-dose intravenous dexamethasone and cyclophosphamide, and immunoablative intravenous cyclophosphamide.167,175–179 All methods were effective in the short-term, although none were curative. Significant side effects, including hematuria, infection, and transitional cell carcinoma of the bladder, were observed with higher dose regimens, although one study using a lower daily dose of cyclophosphamide (1.1–1.5 mg/kg/day) did not report a significantly different safety profile compared with other immunosuppressive agents. Together with the risk of infertility, cyclophosphamide is not generally considered a first-line agent in the treatment of PV.

Dapsone

In a case series and randomized double-blind trial, dapsone demonstrated a trend toward efficacy as a steroid-sparing drug in maintenance phase PV, although these results were not statistically significant.180,181 Dapsone may be used in conjunction with other immunosuppressive agents, particularly rituximab (discussed below), where it offers the additional benefit of Pneumocystis pneumonia prophylaxis.

Additional Therapies

There are additional therapies that can be used when the more standard treatments, discussed previously, are not effective.

Rituximab

A very effective therapy for pemphigus that is refractory to more standard therapy is a monoclonal anti-CD20 antibody rituximab, approved for therapy of B-cell malignancies. In pemphigus patients, this monoclonal antibody presumably targets B cells, the precursors of antibody-producing plasma cells. The B cell also acts to process autoantigen and present it to T cells that provide “help” in stimulating the autoantibody response.182 Rituximab is infused intravenously at a dose of 375 mg/m2 once weekly for 4 weeks. Alternatively, the rheumatoid arthritis dosing regimen can be used (1,000 mg intravenously on day 1 and day 15). The course can be repeated in approximately 6 months for patients with more refractory disease, although a single cycle of rituximab has been shown to be highly effective, with 86% of patients experiencing complete remission lasting 34 months or greater.183 Disease activity usually begins to remit within 1–2 months after the course of therapy. Some experts consider rituximab the therapy of choice for severe pemphigus uncontrolled by corticosteroids and azathioprine or mycophenolate mofetil or who have contraindications to corticosteroids.183,184 However, fatal infections with rituximab therapy have been observed, including Pneumocystis pneumonia, reactivation of hepatitis B, and JC virus infection or reactivation causing progressive multifocal leukoencephalopathy.185–188 Although these complications are rare, some experts recommend Pneumocystis prophylaxis for 1 year following rituximab infusion.

Intravenous Immunoglobulin

Another method of decreasing serum autoantibodies is the intravenous use of γ-globulin (IVIg) in high doses. IVIg is thought to function by saturating circulating neonatal Fc receptor, thereby increasing catabolism of the patient's serum antibodies, which include the pathogenic autoantibodies.189–191 It may be useful as adjuvant therapy in those pemphigus patients whose condition does not respond to more conventional therapy.192,193 A multicenter, randomized, placebo-controlled, double blind study has confirmed its efficacy in pemphigus,194 but it is expensive and probably requires continued infusions for maintenance of remission. There can also be significant side effects with this therapy, including stroke, deep venous thrombosis, and renal failure with sucrose-containing formulations.195 Some centers will use IVIg to establish initial control of blistering in severely affected patients because it does not increase risk of infection as much as corticosteroids and immunosuppressants. IVIg has also been used in combination with rituximab,196 although it is unclear whether the combination is safer or more effective compared to either alone.

Plasmapheresis

Plasmapheresis is sometimes used for severe pemphigus, or for pemphigus that is unresponsive to a combination of prednisone and immunosuppressive agents. Although one controlled study found it to be ineffective,197 other studies have found that it both reduces serum levels of pemphigus autoantibodies and controls disease activity.198 Plasmapheresis plus intravenous pulse therapy with cyclophosphamide has been reported to result in remissions of PV.199 For maximum effectiveness, it is probably necessary to perform plasmapheresis on patients taking immunosuppressive agents to prevent the antibody-rebound phenomenon that can follow the removal of IgG. Protein A immunoadsorption, which removes IgG selectively from plasma, has also been used.200

Pulsed Intravenous High-Dose Glucocorticoids

Intravenous, pulse administration of methylprednisolone, 250–1,000 mg given over approximately 3 hours daily for 4–5 consecutive days, can result in long-term remissions and decrease the total dose of glucocorticoids necessary to control disease.201 Although the purpose of this therapy is to decrease the incidence of complications of long-term steroid use, it can result in all the usual glucocorticoid complications, as well as cardiac arrhythmias with sudden death, and its use is controversial.202 Furthermore, a controlled trial found that adjuvant oral dexamethasone pulse therapy in addition to standard therapy with prednisolone and azathioprine for PV is not beneficial.203 It may be that simply giving divided lower doses of prednisone could accomplish the same result with fewer side effects.

All in all, there has been a tremendous advance in the armamentarium of therapies for pemphigus since the time before the development of glucocorticoids when PV was a fatal disease. Thanks to these advances, the “row of tombstones” seen in the pathology of PV no longer alludes to its prognosis.