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.
Table 3–3Laboratory Evaluation of Systemic Lupus Erythematosus (SLE): General Laboratory Tests ||Download (.pdf) Table 3–3 Laboratory Evaluation of Systemic Lupus Erythematosus (SLE): General Laboratory Tests
|Laboratory Tests ||Results/Significance |
|Complete blood count and erythrocyte sedimentation rate (ESR) ||Decrease in RBC, WBC, and platelets either singly or in combination suggests the presence of autoimmune cytopenias; serial CBC is useful to monitor bone marrow response to immunosuppressive therapy; ESR if elevated is a useful parameter to follow with therapy |
|Urinalysis and BUN/creatinine ||Urinalysis is useful to evaluate proteinuria and any cellular sediments and casts; 24-hour protein excretion and BUN/creatinine are useful to monitor renal function |
|Liver function tests and lipid profile ||For evaluation of possible autoimmune hepatitis; alterations in plasma lipids either due to disease or as a sequelae of therapy are to be appropriately managed to prevent cardiovascular complications |
|VDRL/RPR test for syphilis ||False-positive VDRL test is noted in SLE; a positive VDRL in the absence of syphilis (negative RPR) is a diagnostic criterion for SLE |
|Antinuclear antibody ||95%-98% of patients with active SLE have a positive ANA |
|Complement assay ||C3, C4, and factor B are useful to evaluate complement activation; CH50 to detect congenital complement deficiency especially in familial SLE; low complement values may reflect disease activity |
Table 3–4Autoantibodies and Clinical Associations in Systemic Lupus Erythematosus (SLE) ||Download (.pdf) Table 3–4 Autoantibodies and Clinical Associations in Systemic Lupus Erythematosus (SLE)
|Antigen Specificity ||Prevalence (%) ||Pattern on Hep-2 Cells ||Clinical Associations |
|ds DNA ||40–60 ||Homogeneous ||Marker of active disease; titers fluctuate with disease activity; correlates best with renal disease |
|SS-A/Ro ||40 ||Speckled, fine ||Subacute cutaneous lupus (75%), neonatal lupus with heart block, complements deficiencies and photosensitivity |
|SS-B/La ||10–15 ||Speckled, fine ||Neonatal lupus |
|Sm ||20–30 ||Speckled, coarse ||Specific marker for SLE; may be associated with CNS disease; not useful in monitoring disease activity |
|RNP (U1 RNP) ||30–40 ||Speckled, coarse ||Generally coexists with Sm; RNP is a marker for MCTD |
|Histones ||50–95 ||Homogeneous ||50%-70% in SLE and >95% in drug-induced SLE |
|Phospholipids (beta-2 glycoprotein I antibodies) ||30 ||None specific ||Associated with thrombocytopenia, later trimester abortions, and hypercoagulable states |
|Proliferating cell nuclear antigen (PCNA) ||3 ||Finely granular nuclear staining in rapidly dividing cells ||Not sensitive but specific (>95%); not seen in RA, other connective tissue disease; antibody rapidly diminished by steroids and immunosuppressive drugs; correlates with arthritis |
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:
|Malar rash ||Flat or raised fixed erythema over the malar eminences and sparing the nasolabial folds |
|Discoid rash ||Erythematous raised patches with adherent keratotic scaling and follicular plugging; scarring may occur in older lesions |
|Photosensitivity ||Skin rash resulting from reaction to light |
|Arthritis ||Nonerosive arthritis involving 2 or more peripheral joints that are swollen or tender and evidence of effusion |
|Oral ulcers ||Mostly painless ulcers in the oral cavity and pharynx |
|Serositis ||Pleuritis with pleural rub or effusion; pericarditis documented by rub, EKG change, or pericardial effusion |
|Renal diseases ||Persistent proteinuria greater than 0.5 g/day or 3+ on dipstick or presence on RBC, granular, tubular, or mixed cellular casts |
|Neurologic ||Seizures or psychosis in the absence of metabolic or drug-induced causes |
|Hematologic ||Any immune cytopenia—RBC, WBC, or platelets |
|Immunologic ||Positive anti-ds DNA antibody, positive antiphospholipid antibody, positive anti-Sm antibody, and false-positive serologic test for syphilis |
|Antinuclear antibody ||An abnormal ANA titer by immunofluorescence or an equivalent assay in the absence of drugs known to be associated with “drug-induced lupus” |
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.
Table 3–5Laboratory Evaluation for Sjogren Syndrome ||Download (.pdf) Table 3–5 Laboratory Evaluation for Sjogren Syndrome
| ||Findings in Sjogren Syndrome |
|Diagnostic tests for dry eyes || |
|Schirmer test ||<5 mm wet zone on filter paper in 5 minutes. |
|Rose Bengal dye test ||Visualization of devitalized areas in cornea |
|Tear breakup time ||Measuring breakup time and tear osmolality after installation of fluorescein; identifies those who respond to anti-inflammatory therapy |
|Diagnostic tests for dry mouth || |
|Salivary gland scintigraphy ||Low uptake of radionuclide is specific for SS, but 33% of patients have a positive test; not a sensitive test |
|Lower lip biopsy ||Presence of lymphoid infiltrate around salivary glands is consistent with disease |
|Magnetic resonance imaging (MRI) ||MRI is superior to ultrasonography and CT studies and is equivalent to sialography; correlates well with salivary gland biopsy |
|General laboratory tests || |
|Complete blood count including differential count ||Anemia, neutropenia, lymphopenia, and thrombocytopenia may suggest immune destruction. Marked lymphocytosis may suggest clonal proliferation |
|Serum electrolytes and liver elevated function tests ||Hypokalemia if associated with renal tubular acidosis, elevated alkaline phosphatase suggests primary biliary cirrhosis |
|Erythrocyte sedimentation rate and C-reactive protein ||Markers for chronic and acute inflammation |
|Urinalysis ||Proteinuria, casts imply renal involvement |
|Quantitative immunoglobulins (IgG, IgM, IgA) ||Polyclonal increase is often noted |
|Serum and urine protein electrophoresis (SPEP and UPEP) and serum free light chains with altered kappa/lambda ratio ||Transformation from polyclonal to monoclonal gammopathy implies evolution to a B-cell lymphoma. Presence of urine Bence-Jones protein confirms monoclonal transformation |
|Laboratory tests for autoimmunity || |
|Antinuclear antibody (ANA) titer ||Commonest pattern is speckled; titer greater than 1:160; in 75% of patients |
|Antibodies to SS-A (Ro) ||With ELISA >90% have a positive test |
|Antibodies to SS-B (La) ||With ELISA >90% have a positive test |
|Rheumatoid factor ||70% have positive RF |
|Cryoglobulins, C3, and C4 ||Presence of cryoglobulins and low C3 and C4 are found with multisystem disease |
|Anti-ds DNA antibody ||In 25%-30% of patients with primary SS |
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.
Table 3–6.1Laboratory Evaluation for Systemic Sclerosis/Scleroderma ||Download (.pdf) Table 3–6.1 Laboratory Evaluation for Systemic Sclerosis/Scleroderma
|Laboratory Test ||Scleroderma ||CREST Syndrome |
|Pattern of ANA (Hep-2) ||Speckled ||Centromeric |
|Commonly found autoantibody ||Anti-Scl-70 (greater in diffuse disease than in localized disease) ||Mostly anticentromeric with a distinctive pattern on Hep-2 cells |
Table 3–6.2Autoantigens and Phenotypes in Systemic Sclerosis/Scleroderma ||Download (.pdf) Table 3–6.2 Autoantigens and Phenotypes in Systemic Sclerosis/Scleroderma
|Autoantigens ||Description of Phenotype |
|Scl-70/Topo 1 or topoisomerase 1 ||25%-40% of patients with diffuse scleroderma; associated with severe lung disease |
|ACA or centromere ||55%-96% of patients with CREST syndrome. CENP-B (100%) and CENP-C (50%) are the targets. Seen in Raynaud phenomenon and in about 10% of patients with primary biliary cirrhosis |
|RNA polymerase I, II, and III ||4%-20% of patients with diffuse skin disease and renal involvement and less lung and muscle involvement |
|Fibrillarin (U3 snRNP) ||8%-10% of patients with cardiopulmonary and muscle involvement. Higher prevalence in blacks and Native Americans |
|PM-Scl ||A nucleolar complex seen in association with inflammatory muscle disease in scleroderma |
|Th/To RNP (endoribonuclease) ||10% of patients with limited scleroderma and associated with pulmonary hypertension and fibrosis |
|U1 snRNP (U1 RNP and polypeptides) ||Associated with overlap syndrome and mixed connective tissue disease |
|B-23 (nucleophosmin) ||A nucleolar phosphoprotein associated with pulmonary hypertension and overlap syndrome |
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.
Table 3–7.1Laboratory Evaluation for Inflammatory Muscle Diseases ||Download (.pdf) Table 3–7.1 Laboratory Evaluation for Inflammatory Muscle Diseases
|Test ||Polymyositis ||Dermatomyositis ||Inclusion Body Myositis (IBM) |
|Creatine kinase (CK) ||The CK concentration is elevated >50 times and levels reflect disease activity ||The CK concentration is elevated >50 times and levels reflect disease activity ||CK concentrations may be normal or elevated no more than 10 times the upper limit of normal |
|Muscle biopsy ||The inflammatory infiltrates are usually within the fascicles surrounding the healthy muscle fibers; no perifascicular atrophy; increased CD8+ cells and enhanced expression of major histocompatibility antigens by muscle fibers ||The inflammatory infiltrate is usually around the fascicles. The presence of perifascicular atrophy is diagnostic; complement-mediated vasculopathy is present ||The pattern of inflammation is similar to that seen in polymyositis, with the addition of basophilic-rimmed vacuoles within the muscle fiber sarcoplasm that are characteristic of IBM; the presence of all 3 of the following on muscle biopsy confirms IBM and effectively excludes other idiopathic inflammatory myopathies: 1) vacuolated muscle fibers, 2) muscle fiber inclusions with staining characteristics of beta-amyloid deposits, and 3) demonstration of paired helical fibers by electron microscopy or immunohistological staining |
|Anti-Jo-1 antibodies ||Present in about 40% of patients ||Present in about 40% of patients ||Present in about 40% of patients |
Table 3–7.2Autoantibodies and Phenotypes in Inflammatory Myositis ||Download (.pdf) Table 3–7.2 Autoantibodies and Phenotypes in Inflammatory Myositis
|Autoantibodies ||Description of Phenotype |
|Anti-Jo-1 and other antisynthetases ||Relatively acute onset of myositis, frequent interstitial lung diseases, fever, Raynaud phenomenon, mechanic's hand. Muscle disease dominates the picture in even those who meet criteria for SLE and RA |
|Anti-signal recognition particle (SRP) ||Very acute onset of myositis with severe muscle weakness, predominantly in females and often in autumn. Rash is absent |
|Anti-Mi-2 ||Relatively acute onset of myositis with classical rashes of dermatomyositis such as V sign and shawl sign |
|Anti-200/100 ||Necrotizing myopathy with minimal muscle wasting, preceded by statin therapy, and very high CPK values |
|Anti-155/140 ||Juvenile dermatomyositis and malignancy-associated dermatomyositis |
|Anti-CADM-140 ||Clinically amyopathic dermatomyositis with interstitial lung diseases |
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.
Table 3–8Laboratory Evaluation for Mixed Connective Tissue Disorders ||Download (.pdf) Table 3–8 Laboratory Evaluation for Mixed Connective Tissue Disorders
|Laboratory Tests ||Results |
|Antinuclear antibody ||Speckled pattern on Hep-2 cells |
|Autoantibody to extractable nuclear antigens (ENA) ||Predominantly anti-U1 RNP |
|Autoantibodies for SLE, SS, and polymyositis ||Often positive, except for anti-Sm that is negative |
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
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.
Table 3–9Laboratory Evaluation for Rheumatoid Arthritis ||Download (.pdf) Table 3–9 Laboratory Evaluation for Rheumatoid Arthritis
|Laboratory Test ||Results and Significance |
|Complete blood count (CBC) ||Patients with RA may have a normochromic, normocytic anemia (Hbg of about 10 g/dL), and elevated platelet count with neutrophilia; in Felty syndrome there is neutropenia; patients on immunosuppressive therapy have decreased counts of all lineages |
|ESR ||An index of inflammation and often elevated; in RA patients, its level often parallels disease activity |
|C-reactive protein ||This acute phase reactant is increased in RA and is an index of inflammation; useful in monitoring disease activity over time and in response to therapy |
|Rheumatoid factor (RF) titer ||RF is detectable in 70%-80% of patients with RA; diagnostic utility is limited by its lack of specificity as it is found in almost all patients with cryoglobulinemia, in 70% of patients with Sjogren syndrome, in 20%-30% of those with SLE, and in 5%-10% of healthy individuals; its prevalence increases with age |
|Anti-CCP ||Most useful, as its specificity is 95%-98% and sensitivity is around 85%; predicts erosive disease in RA; valuable in diagnosis of early RA; positive titers to CCP have better predictive value in diagnosis of RA in the IgM-RF-negative subgroup; negative RF in combination with negative anti-CCP is better in excluding RA than either alone in patients with polyarthritis |
|Anti-citrullinated α enolase ||Predictor of radiographic progression |
|Anti-citrullinated fibrin ||Detected in Felty syndrome and vasculitis |
|Matrix metalloproteinase (MMP) 1 and 3 ||Radiographic damage |
|Cartilage oligomeric protein (COMP) ||High levels detected in early RA associated with severe disease of both large and small joints |
|Aggrecan cleavage fragments ||Noted in slow-onset destructive disease of large and small joints |
|Pyridinoline cross-links ||Metabolic marker of activity of bone involvement |
|Serum cryoglobulins ||Presence correlates with extra-articular disease |
|Radiological studies ||Periarticular osteoporosis, soft tissue swelling, joint space reduction and erosions should be determined at baseline and monitored with use of disease-modifying antirheumatic drugs; MRI is sensitive but expensive |
|Joint fluid analysis ||If a single joint exhibits heightened inflammation in a patient with polyarticular disease, need to exclude septic arthritis or crystal-induced arthritis by cell count and differential, culture, and crystal identification |
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.
Table 3–10.1Chemical Classification of Amyloid ||Download (.pdf) Table 3–10.1 Chemical Classification of Amyloid
|Amyloid Protein ||Precursor Protein ||Clinical Syndromes ||Tissues Involved |
|AA ||(Apo) serum AA ||Chronic inflammation, familial mediterranean fever (FMF), familial amyloid nephropathy (FAN) with urticaria and deafness, Muckle-Wells syndrome ||Kidney, liver, and spleen |
|AL ||Ig light chain, kappa or lambda ||Primary or myeloma associated ||Kidney, heart, tongue, bone marrow, and peripheral nerves |
|AH ||Ig heavy chain ||Primary or heavy chain disease associated ||Kidney, heart, tongue, bone marrow, and peripheral nerves |
|ATTR ||Transthyretin ||FAN, familial amyloidotic cardiomyopathy, senile systemic (cardiac) amyloid ||Peripheral and autonomic nerves, heart, and kidney |
|AGel ||Gelsolin ||Corneal lattice dystrophy and cranial neuropathy ||Cornea, cranial and peripheral nerves, kidney |
|ACys ||Cystatin C ||Hereditary cerebral hemorrhage with amyloid ||Cranial vessels |
|Aβ ||Aβ protein precursor (AβPP) ||Alzheimer disease, aging ||Central nervous system |
|Atau ||Tau ||Alzheimer disease, aging, other cerebral conditions ||Brain |
|Aβ2M ||β2-Microglobulin ||Dialysis-related amyloid ||Synovium, carpal tunnel, tongue |
|AApoAI ||Apolipoprotein A-I ||Familial amyloidotic polyneuropathy ||Heart, skin, kidney, nerves, liver, larynx, and blood vessels |
|AApoAII ||Apolipoprotein A-II ||Familial nephropathy ||Kidney |
|ACal ||Procalcitonin ||Medullary thyroid carcinoma ||Thyroid |
|AANF ||Atrial natriuretic factor ||Atrial amyloid of aging ||Cardiac atria |
|AprP ||Prion protein ||Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker disease, fatal familial insomnia ||Central nervous system |
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.
Table 3–10.2Laboratory Evaluation for Amyloidosis ||Download (.pdf) Table 3–10.2 Laboratory Evaluation for Amyloidosis
|Laboratory Tests ||Results/Comments |
|Abdominal fat pad aspiration/biopsy ||Preferred site due to ease of obtaining multiple samples, better yield than rectal biopsy, and less invasive; has replaced rectal biopsy |
|Labial salivary gland biopsy ||Better yield than abdominal pad biopsy for both AL and AA amyloidosis |
|Serum and urine protein electrophoresis ||Primary amyloidosis is often associated with a monoclonal gammopathy; serum and urine electrophoresis followed by immunofixation studies to identify the specific monoclonal protein; assays for serum free light chains and their ratio in serum are essential to detect light chain disease |
|Bone marrow biopsy ||Indicated when serum electrophoresis, serum free light chain assays, and urine electrophoresis indicate a monoclonal gammopathy; flow cytometry and special stains for amyloid facilitate diagnosis |
|Coagulation factor X level ||About 10% of patients with primary amyloidosis have factor X deficiency; about half of the patients with isolated and acquired factor X deficiency have primary amyloidosis; detection of this deficiency prior to biopsy with prothrombin time and factor X assay is essential |
|Protein sequencing ||Useful in identifying genetic abnormalities in hereditary amyloidosis and identifying rare forms of amyloidosis |
|Serum amyloid P (SAP) component scanning ||Scintigraphy with radiolabeled SAP used to identify and estimate total body burden of amyloid; its value is limited because SAP is obtained from blood donors and carries potential infectious risk |
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.
Table 3–11Laboratory Evaluation for Cryoglobulinemia ||Download (.pdf) Table 3–11 Laboratory Evaluation for Cryoglobulinemia
|Laboratory Test ||Comment |
|Cryocrit ||This is the (volume of the cryoprecipitate/volume of serum) × 100; necessary to keep the sample at 37°C until it reaches the laboratory and serum is separated; serum is then refrigerated at 4°C for 72 h; the cryocrit is then measured after centrifugation at 4°C; increased fibrinogen and lipids may lead to falsely elevated values |
|Immunofixation and immunodiffusion ||Used to evaluate the constituents of the cryoglobulin and their clonality, and allow classification as type I, II, or III |
|Urinalysis, BUN, creatinine ||To evaluate renal function |
|C3, C4, and RF ||To assess for complement fixation by RF in the cryoglobulin |
|Liver enzymes ||To evaluate liver function |
|Hepatitis serology ||To evaluate hepatitis B or C infections |
|Renal biopsy and immunofluorescence studies ||Proteinuria, abnormal urinalysis, and altered renal function are an indication for renal biopsy with immunofluorescence for renal pathology |
|Lymph node and bone marrow biopsy ||Indicated when a lymphoproliferative disease is suspected from the type of cryoglobulin, usually type I or II|