Psoriasis is one of the most common dermatologic diseases, affecting up to 1% of the world's population. It is a chronic inflammatory skin disorder clinically characterized by erythematous, sharply demarcated papules and rounded plaques, covered by silvery micaceous scale. The skin lesions of psoriasis are variably pruritic. Traumatized areas often develop lesions of psoriasis (Koebner's or isomorphic phenomenon). In addition, other external factors may exacerbate psoriasis including infections, stress, and medications (lithium, beta blockers, and antimalarials).
The most common variety of psoriasis is called plaque-type. Patients with plaque-type psoriasis will have stable, slowly enlarging plaques, which remain basically unchanged for long periods of time. The most commonly involved areas are the elbows, knees, gluteal cleft, and the scalp. Involvement tends to be symmetric. Plaque psoriasis generally develops slowly and runs an indolent course. It rarely remits spontaneously. Inverse psoriasis affects the intertriginous regions including the axilla, groin, submammary region, and navel; it also tends to affect the scalp, palms, and soles. The individual lesions are sharply demarcated plaques (see Fig. 51-7), but they may be moist and without scale due to their locations.
Guttate psoriasis (eruptive psoriasis) is most common in children and young adults. It develops acutely in individuals without psoriasis or in those with chronic plaque psoriasis. Patients present with many small erythematous, scaling papules, frequently after upper respiratory tract infection with β-hemolytic streptococci. The differential diagnosis should include pityriasis rosea and secondary syphilis.
Pustular psoriasis is another variant. Patients may have disease localized to the palms and soles, or the disease may be generalized. Regardless of the extent of disease, the skin is erythematous with pustules and variable scale. Localized to the palms and soles, it is easily confused with eczema. When generalized, episodes are characterized by fever [39°–40°C (102.2°–104.0°F)] lasting several days, an accompanying generalized eruption of sterile pustules, and a background of intense erythema; patients may become erythrodermic. Episodes of fever and pustules are recurrent. Local irritants, pregnancy, medications, infections, and systemic glucocorticoid withdrawal can precipitate this form of psoriasis. Oral retinoids are the treatment of choice in nonpregnant patients.
Fingernail involvement, appearing as punctate pitting, onycholysis, nail thickening, or subungual hyperkeratosis may be a clue to the diagnosis of psoriasis when the clinical presentation is not classic.
According to the National Psoriasis Foundation, up to 30% of patients with psoriasis have psoriatic arthritis (PsA). There are five subtypes of PsA: symmetric, asymmetric, distal interphalangeal predominant (DIP), spondylitis, and arthritis mutilans. Symmetric arthritis resembles rheumatoid arthritis, but is usually milder. Asymmetric arthritis can involve any joint and may present as "sausage digits." DIP is the classic form, but occurs in only about 5% of patients with PsA. It may involve fingers and toes. Spondylitis also occurs in about 5% of patients with PsA. Arthritis mutilans is severe and deforming. It affects primarily the small joints of the hands and feet. It accounts for less than 5% of PsA.
The etiology of psoriasis is still poorly understood, but there is clearly a genetic component to the disease. Over 50% of patients with psoriasis report a positive family history. Psoriatic lesions demonstrate infiltrates of activated T cells that are thought to elaborate cytokines responsible for keratinocyte hyperproliferation, which results in the characteristic clinical findings. Agents inhibiting T cell activation, clonal expansion, or release of proinflammatory cytokines are often effective for the treatment of severe psoriasis (see below).
Treatment of psoriasis depends on the type, location, and extent of disease. All patients should be instructed to avoid excess drying or irritation of their skin and to maintain adequate cutaneous hydration. Most patients with localized, plaque-type psoriasis can be managed with midpotency topical glucocorticoids, although their long-term use is often accompanied by loss of effectiveness (tachyphylaxis) and atrophy of the skin. A topical vitamin D analogue (calcipotriene) and a retinoid (tazarotene) are also efficacious in the treatment of limited psoriasis and have largely replaced other topical agents such as coal tar, salicylic acid, and anthralin.
Ultraviolet light, natural or artificial, is an effective therapy for many patients with widespread psoriasis. Ultraviolet B (UV-B) light, narrowband UV-B, and ultraviolet A (UV-A) spectrum with either oral or topical psoralens (PUVA) are also extremely effective. The long-term use of UV light may be associated with an increased incidence of nonmelanoma and melanoma skin cancer. UV-light therapy is contraindicated in patients receiving cyclosporine and should be used with great care in all immunocompromised patients due to an increased risk of developing skin cancers.
Various systemic agents can be used for severe, widespread psoriatic disease (Table 52-3). Oral glucocorticoids should not be used for the treatment of psoriasis due to the potential for developing life-threatening pustular psoriasis when therapy is discontinued. Methotrexate is an effective agent, especially in patients with psoriatic arthritis. The synthetic retinoid acitretin is useful, especially when immunosuppression must be avoided; however, teratogenicity limits its use.
Table 52-3 FDA-Approved Systemic Therapy for Psoriasis |Favorite Table|Download (.pdf)
Table 52-3 FDA-Approved Systemic Therapy for Psoriasis
|Agent||Class||Route||Frequency||Adverse Events (Selected)|
|Methotrexate||Antimetabolite||Oral||Weekly||Hepatotoxicity, pulmonary toxicity, pancytopenia, potential for increased malignancies, ulcerative stomatitis, nausea, diarrhea, teratogenicity|
|Acitretin||Retinoid||Oral||Daily||Teratogenicity, osteophyte formation, hyperlipidemia, flare of inflammatory bowel disease, hepatoxicity, depression|
|Cyclosporine||Calcineurin inhibitor||Oral||Twice daily||Renal dysfunction, hypertension, hyperkalemia, hyperuricemia, hypomagnesemia, hyperlipidemia, increased risk of malignancies|
The evidence implicating psoriasis as a T cell–mediated disorder has directed therapeutic efforts to immunoregulation. Cyclosporine and other immunosuppressive agents can be very effective in the treatment of psoriasis, and much attention is currently directed toward the development of biologic agents with more selective immunosuppressive properties and better safety profiles (Table 52-4). Experience with these agents is limited, and information regarding combination therapy and adverse events continues to emerge. Use of tumor necrosis factor (TNF-α) inhibitors may worsen congestive heart failure (CHF), and they should be used with caution in those at risk for or known to have CHF. Further, none of the immunosuppressive agents used in the treatment of psoriasis should be initiated if the patient has a severe infection; patients on such therapy should be routinely screened for tuberculosis. There have been reports of progressive multifocal leukoencephalopathy in association with treatment with the TNF-α inhibitors. Malignancies, including a risk or history of certain malignancies, may limit the use of these systemic agents.
Table 52-4 Biologics Approved for Psoriasis or Psoriatic Arthritis |Favorite Table|Download (.pdf)
Table 52-4 Biologics Approved for Psoriasis or Psoriatic Arthritis
||Once weekly × 12 weeks; may repeat
||Lymphopenia, potential for increased
malignancies, serious infections
||Once or twice weekly
||Serious infections, neurologic events,
hematologic events, potential for increased malignancies
||Every other week
||Serious infections, neurologic events, potential for increased malignancies, hypersensitivity reactions, hematologic events
||Initial infusion followed by infusions at week 2, 6, then every 8 weeks
||Serious infections, hepatotoxicity, hematologic events, hypersensitivity reactions, neurologic events, potential for increased malignancies
Lichen planus (LP) is a papulosquamous disorder that may affect the skin, scalp, nails, and mucous membranes. The primary cutaneous lesions are pruritic, polygonal, flat-topped, violaceous papules. Close examination of the surface of these papules often reveals a network of gray lines (Wickham's striae). The skin lesions may occur anywhere but have a predilection for the wrists, shins, lower back, and genitalia (Fig. 52-5). Involvement of the scalp, lichen planopilaris, may lead to scarring alopecia, and nail involvement may lead to permanent deformity or loss of fingernails and toenails. LP commonly involves mucous membranes, particularly the buccal mucosa, where it can present a spectrum of disease from a mild, white, reticulate eruption of the mucosa to a severe, erosive stomatitis. Erosive stomatitis may persist for years and may be linked to an increased risk of oral squamous cell carcinoma. Cutaneous eruptions clinically resembling LP have been observed after administration of numerous drugs, including thiazide diuretics, gold, antimalarials, penicillamine, and phenothiazines, and in patients with skin lesions of chronic graft-versus-host disease. In addition, LP may be associated with hepatitis C infection. The course of LP is variable, but most patients have spontaneous remissions 6 months to 2 years after the onset of disease. Topical glucocorticoids are the mainstay of therapy.
Lichen planus. An example of lichen planus showing multiple flat-topped, violaceous papules and plaques. Nail dystrophy as seen in this patient's thumbnail may also be a feature. (Courtesy of Robert Swerlick, MD; with permission.)
Pityriasis rosea (PR) is a papulosquamous eruption of unknown etiology occurring more commonly in the spring and fall. Its first manifestation is the development of a 2- to 6-cm annular lesion (the herald patch). This is followed in a few days to a few weeks by the appearance of many smaller annular or papular lesions with a predilection to occur on the trunk (Fig. 52-6). The lesions are generally oval, with their long axis parallel to the skinfold lines. Individual lesions may range in color from red to brown and have a trailing scale. PR shares many clinical features with the eruption of secondary syphilis, but palm and sole lesions are extremely rare in PR and common in secondary syphilis. The eruption tends to be moderately pruritic and lasts 3 to 8 weeks. Treatment is directed at alleviating pruritus and consists of oral antihistamines; midpotency topical glucocorticoids; and, in some cases, the use of UV-B phototherapy.
Pityriasis rosea. In this patient with pityriasis rosea, multiple round to oval erythematous patches with fine central scale are distributed along the skin tension lines on the trunk.