+++
Systemic Lupus Erythematosus
++
Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease, associated with the production of antibodies to a variety of nuclear and cytoplasmic antigens. The hallmark characteristic is the generation of antibodies to ds DNA. These antibodies complex to these self-antigens, and the ensuing immune complexes contribute to the inflammation in many organs, particularly the skin, joints, kidney, and, to a lesser extent, the cardiovascular and nervous systems, lung, and hemopoietic cells.
++
The disease is more common in women than in men and usually appears in early adulthood, although it is seen in children as well. It not only is more common in African Americans than in Caucasians but also has a more severe clinical phenotype with renal and vasculitic manifestations in African Americans.
++
The candidate genes associated with SLE include those coding for complement components C1q, C4A, C2, activating and inhibitory FcγR, interferon regulatory factor 5 (IRF5), TNF, MHC class II (DR2 and DR3), and programmed cell death PDCD1, among others.
++
Table 3–3 summarizes the laboratory evaluation of SLE and Table 3–4 lists the autoantibodies associated with SLE.
++
++
++
According to the American Rheumatologic Association criteria for diagnosis of SLE, the diagnosis of SLE is made if 4 or more of the following 11 criteria are present at any time during the course of the disease:
++
++
Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease, associated with the production of antibodies to a variety of nuclear and cytoplasmic antigens. The hallmark characteristic is the generation of antibodies to ds DNA.
++
Tests utilized in the initial evaluation and subsequent monitoring of patients with SLE are shown in Tables 3–3 and 3–4 and Figure 3–1.
++
Sjogren syndrome (SS) is a systemic connective tissue disease, more common in women than in men. Pathologically, it is an autoimmune exocrinopathy involving the lacrimal glands, salivary glands, and less often the pancreas. The immune inflammation of these glands contributes to the sicca syndrome, with dry eyes (keratoconjunctivitis) and dry mouth (xerostomia) as characteristic clinical features. The disease can be primary or secondary. The primary syndrome is characterized by dry eyes, dry mouth, decreased production of tears as tested by the Schirmer test, and a lip biopsy that demonstrates inflammation of the minor salivary glands. Serologically, patients with primary Sjogren show a positive ANA, positive SS-A (Ro), positive SS-B (La), and positive rheumatoid factor (RF) in the absence of another connective tissue disease. A prospective study of 80 patients with primary SS followed for a median of 7.5 years reported the following frequencies of clinical manifestations: a) keratoconjunctivitis sicca and/or xerostomia occurred in all patients and were the only disease manifestations in 31%; b) extraglandular involvement occurred in 25%; and c) non-Hodgkin lymphoma developed in 2.5%. Secondary SS is clinically similar to the primary disorder, but it is additionally associated with clinical and serologic features of another connective tissue disease, such as rheumatoid arthritis (RA) or scleroderma.
++
The diagnostic features are revealed by tests that document the sicca features. The dry eyes are evaluated by the Schirmer test. This test is a measurement of tear flow over a 5-minute period. Filter paper is allowed to hang from the lateral inferior eyelid and the length of the paper that becomes wet is measured. This test is not reliable, as early in the disease there is excessive lacrimation giving a false-negative test. Demonstration of devitalized corneal epithelium due to keratoconjunctivitis is evaluated by rose Bengal or fluorescein stain. The most accurate test is the slit lamp examination of the cornea and conjunctiva. Tests for quantitating salivary secretion are not standardized and also are not specific to SS. Biopsy of the minor salivary gland in the lower lip demonstrating focal lymphocytic infiltration is a useful confirmatory test.
++
Systemic sclerosis is characterized by excessive and often widespread deposition of collagen in many organ systems of the body. Pathologically, the hallmark is the deposition of altered collagen in the extracellular matrix and a proliferative and occlusive small vessel vasculopathy.
++
Table 3–5 summarizes the laboratory tests useful in diagnosis of both primary and secondary SS.
++
+++
Systemic Sclerosis/Scleroderma
++
Systemic sclerosis is characterized by excessive and widespread deposition of collagen in many organ systems of the body. The hallmark of this pathologic process is the deposition of altered collagen in the extracellular matrix. The disorder is characterized pathologically by 3 features: 1) tissue fibrosis; 2) a proliferative and occlusive vasculopathy of the small blood vessels; and 3) a specific autoimmune response associated with distinctive autoantibody profile.
++
The immunologic basis is not well understood, but an aberration in TGF-beta-mediated deposition of collagen has been observed. Antibodies to platelet-derived growth factor receptors have been incriminated in the development of fibrosis. Both the triggering event and genetic predisposition are not well defined. Although the common organ involved is the skin, the gastrointestinal tract, kidney, lung, and muscles are also affected as the disease progresses. Renal ischemia leading to hypertension escalates the complications of this disease. Preponderance in females is common.
++
Clinically there are 4 major subtypes described:
++
Diffuse cutaneous scleroderma with widespread involvement of skin and visceral organs.
Limited cutaneous scleroderma, in which the disease is limited to the digital extremities and face. CREST syndrome is a variant of this entity. The name is derived from its features—calcinosis, Raynaud syndrome, esophageal dysmotility, sclerodactyly, and telangiectasia.
Localized scleroderma that affects primarily the skin of the forearms, the fingers, and later the systemic organs.
Overlap syndromes with features of RA or muscle involvement.
++
Ninety percent to 95% of all patients with scleroderma have a positive ANA test. The most common pattern is finely speckled, followed by centromeric and nucleolar patterns. The ANA activity is directed against DNA topoisomerase (also known as Scl-70). A definitive diagnosis is achieved when the characteristic clinical findings are accompanied by a positive ANA test, and often confirmed by an antibody directed to Scl-70 by ELISA.
++
Sjogren syndrome is characterized by immune-mediated destruction of exocrine glands, particularly the salivary and lacrimal glands, with secondary development of keratoconjunctivitis and xerostomia. A positive ANA along with antibodies to SS-A (Ro) and/or SS-B (La) is a serologic feature. Transition from a polyclonal rheumatoid factor (RF) positive to a RF-negative oligoclonal or monoclonal process suggests a malignant lymphomatous transformation.
++
Tables 3–6.1 and 3–6.2 summarize the laboratory evaluation for systemic sclerosis/scleroderma.
++
++
+++
Inflammatory Muscle Diseases
++
Inflammation of the muscle leading to injury and weakness is the basis of the 3 most common but distinct diseases in this category. They are dermatomyositis (DM), polymyositis (PM), and inclusion body myositis. These diseases are more common in women, and their etiology remains unknown, although immune mechanisms have been incriminated. DM may occur as a specific entity or be associated with scleroderma or mixed connective tissue disease. Rarely, it is a manifestation of a malignancy. Skin manifestations such as a heliotrope rash, the shawl sign, and Gottron papules are common in DM. Like DM, PM may also be associated with another connective tissue disease. In addition, it may be associated with viral, parasitic, or bacterial infections. DM is characterized by immune complex deposition in the vessels and is considered to be in part a complement-mediated vasculopathy. In contrast, PM appears to reflect direct T-cell-mediated muscle injury. Inclusion body myositis is a disease of older individuals and is not associated with malignancy. It is occasionally associated with another connective tissue disease.
++
Inflammation of the muscle leading to injury and weakness is the basis of the 3 most common but distinct diseases in this category. They are dermatomyositis (DM), polymyositis (PM), and inclusion body myositis.
++
Antisynthetase syndrome, characterized by antisynthetase antibodies that are highly specific for DM and PM, is seen in about 30% of patients with DM or PM. These patients typically experience a relatively acute onset of disease, constitutional symptoms such as fever, Raynaud phenomenon, arthritis, and interstitial lung diseases. Their hands exhibit a roughening and cracking of the radial sides of the fingers and the palm, resembling a condition found in people who labor with their hands such as mechanics, and hence called “mechanic's hands.” HLA DR 52 has a strong association (90%) with antisynthetase antibody-positive myositis in people of both European and African descent. The antisynthetase antibodies include antibodies to aminoacyl-tRNA synthetase; antihistidyl-tRNA synthetase, also known as Jo-1; anti-signal recognition particle (SRP) antibodies directed against SRP; and anti-Mi-2 antibodies directed against a helicase involved in transcriptional activation.
++
Although there are several common features between DM and PM, a characteristic feature of DM itself is the heliotrope hue around the eyes. Pulmonary interstitial fibrosis is seen in about 10% of cases in both diseases, occurring in the context of antisynthetase syndromes. There are 5 distinctive features described for both of these diseases. At least 3 of the following features are essential to fulfill the clinical diagnostic criteria for each:
++
Proximal and symmetrical muscle weakness
History of muscle pain and tenderness on palpation
Electromyographic evidence of spontaneous muscle activity and myopathic changes
Elevated serum or plasma concentrations of muscle enzymes such as aldolase, creatinine kinase (CK), and AST
Muscle biopsy demonstrating cellular inflammation
++
The laboratory diagnosis begins with documentation of muscle inflammation and injury as shown by elevation of serum or plasma concentrations of muscle enzymes such as aldolase, CK, and AST, together with the expected inflammatory histological features on muscle biopsy. The detection of autoantibodies is found in about one third of the patients, and supports a diagnosis of inflammatory muscle disease. The antibodies are directed at tRNA synthetases. Anti-Jo-1 is such an antibody, with specificity to histidyl-tRNA synthetase. It is found in about 40% of patients with PM, and generally indicates a worse prognosis. It is also more commonly found in patients with pulmonary fibrosis. Jo-1 is more commonly detected in cases of autoimmune myositis than in those with other causes of muscle inflammation. As with many autoimmune diseases, the integration of clinical features with laboratory findings forms the basis of definitive diagnosis. Tables 3–7.1 and 3–7.2 present the laboratory evaluation for inflammatory muscle disorders.
++
++
++
The entity known as mixed connective tissue disorder (MCTD) has some of the features of SLE, some of systemic sclerosis, and some of polymyositis.
+++
Mixed Connective Tissue Disease
++
The entity known as mixed connective tissue disease (MCTD) has some of the features of SLE, some of systemic sclerosis, and some of PM. The patients have variable clinical presentations with arthralgias, myalgias, fatigue, and Raynaud phenomenon. These features are superimposed on other findings that can add in over time, including malar rash, sclerodactyly, arthritis of the hands, and Raynaud phenomenon. Pulmonary manifestations occur in over 85% of these patients and include interstitial pneumonitis, pulmonary hypertension, progressive interstitial fibrosis, and, rarely, dysfunction of diaphragm and esophagus. On rare occasion, patients with MCTD develop diffuse proliferative glomerulonephritis, psychosis, or seizures. The appropriate constellation of clinical findings suggests the need for laboratory testing, described in Table 3–8.
++
++
The diagnosis of MCTD is largely made on the basis of the clinical features consistent with multiple autoimmune diseases. It is supported by a high titer of anti-U1 RNP in the serum.
++
RA is a systemic autoimmune connective tissue disorder that primarily affects the synovial joints, often starting as a synovitis. It affects 1% to 2% of the adult population worldwide, and is predominantly a disease of young women. Susceptibility and resistance to RA is associated with HLA genotypes. The criteria for diagnosis of RA were revised in 1987 to include clinical features, laboratory values, and radiographic findings. To establish a definitive diagnosis, at least 3 of the following 7 criteria must be present along with morning stiffness for a period of at least 6 weeks:
++
RA is a systemic autoimmune connective tissue disorder that primarily affects the synovial joints, often starting as a synovitis. It affects 1% to 2% of the adult population worldwide, and is predominantly a disease of young women.
++
Arthritis in 3 or more small joints
Morning stiffness lasting >30 minutes
Arthritis of the small joints of the hand
Rheumatoid nodules
Symmetrical arthritis, often with synovitis
A positive test for RF
Radiographic changes of the affected joints
++
An increased serum titer of RF has been a long-standing marker of RA, until the validation of anti-cyclic citrullinated peptide antibody (anti-CCP). This antibody not only is highly associated with RA but is also a marker for progressive and erosive joint disease. Anti-CCP is approximately 98% specific and 85% sensitive as a serum marker for RA. RF is an IgM autoantibody directed against the Fc region of IgG. While high titers of RF are associated with severe RA, it is not specific for diagnosis of RA, as it is also found in chronic infections and other connective tissue diseases. Table 3–9 summarizes the laboratory tests useful in the evaluation of RA.
++
++
Amyloidosis and cryoglobulinemia (which follows) are systemic diseases resulting from the deposition in the tissues of insoluble proteins from a soluble circulating precursor. Both represent the consequences of immune dysregulation, and their diagnosis depends on laboratory evaluation and confirmation.
++
Amyloidosis is a heterogeneous group of diseases resulting from the extracellular deposition of low-molecular-weight fibrils from a soluble circulating precursor giving a “waxy” or “lardaceous” appearance to the infiltrated organs. Ultrastructurally, amyloid deposits are composed of unbranching fibrils 8 to 10 nm in width and with a molecular weight of 5 to 25 kd. At least 25 biochemically distinct forms of human amyloid protein have been identified. The 2 most common forms are primary, with amyloid light chain (AL) derived from light chains of plasma cells, and secondary, with amyloid-associated protein (AA), a nonimmunoglobulin protein. Congo red staining of amyloid deposits demonstrates a characteristic apple-green birefringence on polarized microscopy, while staining with Thioflavin T produces yellow-green fluorescence.
++
The classification of amyloidosis is based on whether the amyloidosis is associated with a plasma cell dyscrasia such as multiple myeloma or light chain myeloma (primary amyloidosis), or the sequelae of an infectious or inflammatory disease (secondary or reactive amyloidosis). Amyloidosis may also be classified as hereditary or acquired, localized or systemic, or by the type of fibril deposited in tissues, such as transthyretin (TTR) and Alzheimer amyloid precursor protein (APP). A partial list of the chemical classification of human amyloid is given in Table 3–10.1.
++
++
The diagnosis of amyloidosis is based on the histological and immunochemical demonstration of amyloid deposits in affected organs and tissues. The preferred tissue for biopsy is obtained by fine needle aspiration of the abdominal fat pad.
++
The most common form of the disease, representing 75% to 80% of the cases, is primary amyloidosis, as an acquired disorder, with multiorgan systemic involvement. Primary amyloidosis has a male to female preponderance of 2:1. Its incidence increases with age, often starting at age 40 years.
++
Reactive amyloidosis or type AA amyloidosis is a serious outcome of a group of diseases called autoinflammatory syndromes. This group of diseases represents too much inflammation secondary to dysregulation of the innate immune system, in the absence of high-titer autoantibodies or antigen-specific T cells. The hereditary autoinflammatory syndromes, also known as hereditary periodic fever syndromes, represent a group of genetic disorders characterized by recurrent inflammatory episodes of noninfectious origin, often starting in childhood and persisting lifelong. These syndromes are characterized by a variety of features that include fever, abdominal symptoms, arthralgias, arthritis, lymphadenopathy, and skin manifestations. An exuberant acute phase response with elevated C-reactive protein (CRP), serum amyloid A (SAA), and leukocytosis is associated with the inflammatory clinical presentation. The soluble SAA protein is degraded to the insoluble fibrils composed of AA, which is the hallmark of secondary amyloidosis. The mutated genes in these syndromes all code for proteins that play a role in the regulation of innate immunity.
++
The diagnosis of amyloidosis is based on the histological and immunochemical demonstration of amyloid deposits in affected organs and tissues. The preferred tissue for biopsy is obtained by fine needle aspiration of the abdominal fat pad. Its advantages over rectal biopsy are that multiple samples can be obtained for study, and it is less painful and invasive. Since a plasma cell dyscrasia is commonly found in patients with amyloidosis, a serum protein electrophoresis together with a determination of serum free kappa and lambda light chains by nephelometry and a calculation of the kappa/lambda ratio is necessary to exclude a monoclonal gammopathy as the cause of the amyloidosis. Amyloid fibrils may bind to coagulation factor X causing a coagulopathy. Determination of the factor X level is important to explain bleeding tendencies in amyloidosis patients and is useful prior to biopsy of organs and tissues to identify a coagulopathy that would permit excess bleeding at the biopsy site.
++
To define the extent of the disease and the type of amyloidosis, the patient should be evaluated for renal, cardiac, pulmonary, neurologic, cutaneous, articular, liver, and spleen involvement. Cardiac involvement is extremely common in primary amyloidosis and much less in secondary amyloidosis. Virtually all of the familial amyloidosis manifests with nephropathic, neuropathic, or cardiopathic features. Laboratory evaluation for amyloidosis is summarized in Table 3–10.2.
++
++
Cryoglobulinemia refers to the presence in the serum of 1 or more immunoglobulins that precipitate at a temperature below 37°C. This precipitation is reversible, as it redissolves on warming to 37°C. The cause of cryoprecipitation remains to be determined.
++
Cryoglobulinemia refers to the presence in the serum of 1 or more immunoglobulins that precipitate at a temperature below 37°C. This precipitation is reversible, as it redissolves on warming to 37°C.
++
Cryoglobulins are classified into 3 types. Type I consists of a single monoclonal immunoglobulin that does not have RF activity. It is typically IgM or IgG and less often IgA. Type I, also called simple cryoglobulinemia, is often associated with lymphoproliferative malignancies such as Waldenstrom macroglobulinemia or multiple myeloma. Patients with this disorder may present with features of vasculopathy involving the digits, resulting in gangrene. Type II consists of monoclonal IgM RF mixed with polyclonal IgG or IgA. The most common association for this form of cryoglobulinemia is hepatitis C infection. Type II may rarely be associated with lymphoma. Type III is also a mixed cryoglobulinemia, with polyclonal IgM RF associated with polyclonal IgG or IgA. Type III is found in patients with connective tissue disease and chronic infections. Both type II and III cryoglobulinemia patients may show fixation of complement and be associated with hypocomplementemia. Immune complex vasculitis, arthritis, neuropathy, and renal involvement may be the presenting features in patients with type II or III cryoglobulinemia.
++
When present, the cryoglobulins are quantitated using a Wintrobe tube, and the amount of cryoglobulin present is reported as a cryocrit. It is important to remember that it is not the quantity as reported by a cryocrit that is important, but the biological inflammatory properties of the cryoglobulin. This inflammatory potential is reflected by hypocomplementemia, tissue inflammation, and organ injury. With therapy, the cryocrit decreases along with mitigation of inflammatory markers such as CRP, ESR, and complement activation. When a cryoglobulin is identified, the components comprising the cryoprotein are identified by immunodiffusion and immunofixation, using specific antisera directed at the immunoglobulin isotypes and against C3 and C4. Based on the clonality and the constituent isotypes, the cryoglobulin is then categorized as type I, II, or III. Table 3–11 summarizes the laboratory evaluation for cryoglobulinemia.
++