Approach Considerations
Laboratory studies are not helpful in establishing a diagnosis of serum sickness. However, certain laboratory findings have been reported, including the following:
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Leukopenia or mild leukocytosis, with or without eosinophilia
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Plasma cells on peripheral blood smear [2]
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Erythrocyte sedimentation rate elevation [2]
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Polyclonal gammopathy or a transient monoclonal immunoglobulin G (IgG) spike [4]
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Mild proteinuria or hematuria
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Transient elevation of serum creatinine levels
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Decreased complement levels (C3, C4) [2]
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Cryoglobulinemia, often of the mixed (IgM-IgG) type
Histologic Findings
Numerous histological changes may be found in serum sickness, depending on the organ involved and, possibly, the nature of the antigen. The tissues most commonly involved include those of the heart, arteries, joints, and kidneys. Arteritic lesions are focal, necrotizing, and inflammatory processes that usually involve all layers of the artery.
Acute inflammatory exudate, necrosis of the arterial wall, fibrinoid material, or primarily a mononuclear reaction may be observed. Joints may have focal mononuclear infiltrates with edema and fibrinoid formation in the synovial tissues. Kidneys develop endothelial proliferation of the glomerular capillaries with slight basement membrane thickenings. [6]
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A 29-year-old woman with RA presented with fever, a diffuse skin rash, and arthralgia approximately 10 days after receiving intravenous rituximab. Diagnosis was rituximab-associated serum sickness. Image courtesy of Jason Kolfenbach, MD, and Kevin Deane, MD, Division of Rheumatology, University of Colorado Denver School of Medicine.
