What is exanthem?

What is Exanthem?

Exanthem is a widespread skin rash that typically presents as multiple inflammatory skin alterations with hematogenic, lymphogenic, or neurogenic origin, often associated with systemic infections, drug reactions, or immune-mediated processes. 1

Types and Causes of Exanthems

Exanthems can be classified into several categories:

Viral Exanthems

• Classic childhood viral exanthems: Measles, rubella, varicella (chickenpox), erythema infectiosum (fifth disease) 1, 2
• Atypical viral exanthems: Caused by various viruses including Epstein-Barr virus (EBV), human herpesvirus 6 (HHV6), and cytomegalovirus (CMV) 3

Drug-Induced Exanthems

• Common with beta-lactam antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) 3
• Often present as papulopustular eruptions, especially with EGFR inhibitors and MEK inhibitors in cancer treatment 4

Bacterial Exanthems

• Rocky Mountain Spotted Fever (RMSF) presents with a characteristic rash that typically appears 2-4 days after fever onset 4
• Other bacterial causes include Mycoplasma pneumoniae 3

Clinical Presentation

The presentation of exanthems varies based on the underlying cause:

Morphology and Distribution

• Viral exanthems: Often begin as small, blanching, pink macules that may evolve to maculopapules 4, 2
• Drug-induced exanthems: May present as follicular papules and pustules, particularly in areas with high density of sebaceous glands (face, chest, upper back) 4
• RMSF exanthem: Begins as small, blanching, pink macules on extremities that evolve to maculopapules and potentially petechiae, with classic centripetal spread 4

Associated Symptoms

• Fever, pruritus, stinging, pain 4
• Systemic symptoms may include headache, myalgia, and in severe cases, neurological manifestations 4

Diagnostic Approach

Distinguishing between different types of exanthems requires:

1. Detailed history: Timing of rash in relation to fever onset, medication use, recent exposures
2. Physical examination: Characterization of rash morphology, distribution pattern, progression
3. Laboratory testing: When indicated, may include:
   • Virological laboratory diagnosis for atypical infectious diseases 1
   • Bacterial cultures when infection is suspected 4
   • Serological and PCR assays for specific viral pathogens 3

Management Principles

Management depends on the underlying cause:

For Drug-Induced Papulopustular Exanthema

1. Preventive measures:

   • Avoid frequent washing with hot water
   • Avoid skin irritants
   • Use alcohol-free moisturizers twice daily
   • Avoid excessive sun exposure
   • Use sun protection 4

2. Treatment based on severity:

   • For mild to moderate cases: Topical corticosteroids and oral tetracycline antibiotics
   • For severe cases: Systemic corticosteroids and interruption of the causative medication 4

For Infectious Exanthems

• Specific antimicrobial therapy when indicated
• Supportive care for viral exanthems that are self-limiting 1

Important Considerations

• Exanthems may be the first sign of potentially serious conditions, requiring prompt diagnosis and treatment 5
• The distinction between virus-induced and drug-induced skin eruptions is often difficult during the acute phase 3
• Making a correct etiological diagnosis is crucial for both patient care and public health concerns (e.g., school exclusion, immunization recommendations, pregnancy risks) 6

Common Pitfalls to Avoid

1. Misattribution: A rash on the palms and soles is not pathognomonic for RMSF and can occur in various conditions including drug reactions and other infections 4

2. Missing atypical presentations: Rash might be completely absent or atypical in up to 20% of RMSF cases 4

3. Overlooking secondary infections: Drug-induced exanthems may become secondarily infected, requiring additional antimicrobial treatment 4

4. Premature diagnosis: Viral exanthems occurring while children are taking medication can mimic drug exanthems and may be incorrectly labeled as drug allergies in approximately 10% of cases 3