Serum sickness

Background

• A type III hypersensitivity reaction (secondary to injection of anitoxins e.g. tetanus, rabies)
• Reactions secondary to the administration of nonprotein drugs (e.g. Amoxicillin, cefaclor, cephalexin (Keflex), trimethoprim-sulfamethoxazole)
• Primary occurs 6-21 days after initial exposure
  • 1-4 days after subsequent exposures to the same antigen
• Symptoms usually last 1-2 weeks before spontaneously subsiding
• Long-lasting sequelae generally do not occur
• Fatalities are rare and usually are due to continued administration of the antigen

Clinical Features

• Fever
• Arthralgia
• Lymphadenopathy
• Skin eruption (rash)
  • Urticaria
  • Scarlatiniform rash
  • Maculopapular or purpuric lesions
  • Erythema multiforme

Differential Diagnosis

• Erythema multiforme
• Mononucleosis
• Polymyositis
• Systemic Lupus Erythematosus
• Tick borne illnesses, Rocky Mountain Spotted Fever
• Toxic Epidermal Necrolysis

Polyarthritis

Algorithm for Polyarticular arthralgia

• Fibromyalgia
• Juvenile idiopathic arthritis
• Lyme disease
• Osteoarthritis
• Psoriatic arthritis
• Reactive poststreptococcal arthritis
• Rheumatoid arthritis
• Rheumatic fever
• Serum sickness
• Systemic lupus erythematosus
• Serum sickness–like reactions
• Viral arthritis

Evaluation

• Clinical diagnosis in which labs may be suggestive but not required
  • Careful investigation of new medications
  • List of serum sickness medications
• Mild leukopenia or leukocytosis
• ESR elevation
• Mild proteinuria
• Mild hematuria
• Mild serum creatinine elevation
• Decreased C3, C4
• Other labs to obtain:
  • CH50
  • LFTs
  • Urine electrolytes (Na, K, Cr, eosinophils)
  • ESR and CRP
  • Viral hepatitis panel, HIV, RPR/VDRL

Management

• Discontinue antigen
• Antipyretics
• Diphenhydramine
• Prednisone

Disposition

• Admit for:
  • Significant comorbidities (advanced or very young age, immunocompromised)
  • Severe symptoms
  • Hemodynamic instability/hypotension
  • Unclear diagnosis