Systemic Lupus Erythematosus: The Devastatingly Deceptive Disease
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Expires July 31, 2017
Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that often goes undiagnosed initially. Timely detection of SLE is important, because prompt treatment can prevent its many major complications—notably, end organ damage. Here’s how to distinguish SLE from other illnesses with similar presentations and how to recognize the complications of undiagnosed SLE, which can progress rapidly and fatally.
LABORATORY WORK-UP
Laboratory abnormalities associated with SLE include anemia, leukopenia, lymphopenia, thrombocytopenia, hypocomplementemia, and proteinuria. A typical work-up includes a routine complete blood count (CBC) with differential, serum creatinine, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), urinalysis with microscopy, and serologic ANA titer.1,16,19 A CBC with differential may reveal hematologic abnormalities, such as anemia of chronic disease (most commonly) or autoimmune hemolytic anemia, as well as leukopenia and thrombocytopenia due to circulating autoantibodies.3 An elevated ESR and CRP indicate the severity of the systemic inflammation and/or infection. Urinalysis is effective for detecting lupus with renal diseaseand may reveal proteinuria due to renal dysfunction.2
A positive ANA titer indicates widespread activation of the immune system targeted against nuclear and cytoplasmic subparticles. The vast majority of patients with SLE will develop a positive ANA with a high titer at some point during the course of their disease.16 The ANA is highly sensitive for SLE (93% to 95%) but lacks specificity (57%).20The most common tests for ANA are enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence assay (IFA). ELISA is more sensitive in detecting ANA, while IFA is the gold standard due to its high specificity.21 Some laboratories may use immunoassay as a screening tool for ANA and then use IFA to confirm positive or equivocal results.21 Positive ANA results can be seen in patients with other rheumatologic diseases and in up to 15% of all healthy persons, but with low or borderline titers.22 For these reasons, ANA testing alone is a poor predictor of SLE.
When either the ANA test results are positive or are negative but a strong clinical suspicion for SLE remains, clinicians should order tests for antibodies to extractable nuclear antigens (ENA panel; see Table 2).3,16 Anti-dsDNA and anti-Smith (anti-Sm) antibodies are both specific for SLE, and levels of anti-dsDNA reflect disease activity in many patients.1,19 In contrast, anti-dsDNA antibodies are found in fewer than 0.5% of healthy individuals and patients with other autoimmune conditions.19 Among patients with high levels of anti-dsDNA antibodies and clinically inactive disease, 80% will have active disease within five years after elevated antibodies are detected.19
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Autoantibodies, including ANA, anti-SSA/Ro, anti-SSB/La, and antiphospholipid antibodies, are usually detectable for many years prior to the onset of symptomatic SLE, while others, such as anti-Sm and anti-U1RNP, appear just months before the diagnosis.23 Patients with positive ANA results who do not meet criteria for SLE are still at risk for lupus and other autoimmune diseases, because complex autoimmune changes occur years before the diagnosis of SLE.23 These patients should be followed closely.
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