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
  • Amoxicillin, cefaclor, cephalexin (Keflex), trimethoprim-sulfamethoxazole

Clinical Features

• Primary occurs 6-21 days after exposure
  • 1-4 days after subsequent exposures to the same antigen
• 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 Diseases, 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 extensive
• Mild leukopenia or leukocytosis
• ESR elevation
• Mild proteinuria
• Mild hematuria
• Mild serum Cr elevation
• Decreased C3, C4
• Other labs to obtain:
  • CH50
  • LFTs
  • Urine electrolytes (Na, K, Cr, eosinophils)
  • ESR and CRP
  • HepB, HepC panel, HIV, RPR/VDRL

Management

• Discontinue antigen
• Antipyretics
• Diphenhydramamine
• Prednisone

Disposition

Admit for:

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

Prognosis

• 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