Introduction

Essentials of Diagnosis

• Fever, pruritus, and arthropathy.
• Reaction is delayed in onset, usually 7-10 days, when specific IgG antibodies are generated against the allergen.
• Immune complexes found circulating in serum or deposited in affected tissues.

General Considerations
Serum sickness reactions occur when immune complexes are formed by the binding of antigens (eg, drugs, heterologous serum) to antibodies. Deposition of these complexes in tissues or in vascular endothelium can produce immune complex-mediated tissue injury by activation of complement, generation of anaphylatoxins, chemoattraction of polymorphonuclear leukocytes, and tissue injury. The commonly affected organs include skin (urticaria, vasculitis), joints (arthritis), and kidney (nephritis).

 

Clinical Findings

A. Symptoms and Signs
Constitutional symptoms, such as drug fever, are common.

B. Laboratory Findings
The specific IgG antibody may be present in sufficient quantity in serum to be detected by the precipitin-in-gel method. Detection of these precipitating antibodies by gel diffusion can be useful in the diagnosis of allergic bronchopulmonary aspergillosis or hypersensitivity pneumonitis. ELISA will detect antibodies present in lesser amounts.

Circulating antigen-nonspecific immune complexes can be detected in a variety of malignancies and in autoimmune, hypersensitivity, and infectious diseases. Immunohistochemical techniques can identify immune complexes or complement fragments deposited in tissue biopsy specimens. Depressed serum levels of C3, C4, or CH50 may be sought as nonspecific evidence of immune complex disease with consumption of soluble factors.

The erythrocyte sedimentation rate is increased, and other nonspecific laboratory findings may include elevated hepatic aminotransferases or reduced complement levels. Circulating immune complexes may be found, but current assays are limited in sensitivity. Evidence of nephritis may be found by observing red cell casts at urinalysis.

Treatment
This disease is self-limited, so treatment is usually conservative. Aspirin will relieve the arthralgias. Antihistamines and topical steroids will control the dermatitis. Corticosteroid therapy may be necessary for serious reactions -  especially glomerulonephritis, neuropathy, and other manifestations of vasculitis.