Which viral exanthems cause a palmar rash in patients?

Viral Exanthems Causing Palmar Rash

The primary viral exanthems that cause palmar rash are enteroviruses, specifically coxsackievirus and echovirus, which cause hand, foot, and mouth disease (HFMD), though it is critical to immediately exclude life-threatening bacterial causes like Rocky Mountain Spotted Fever and meningococcemia before attributing the rash to a benign viral etiology. 1

Primary Viral Causes

Enteroviruses (Most Common)

• Coxsackievirus A16 and enterovirus 71 are the classic causes of HFMD, presenting with characteristic vesicular lesions on palms and soles that begin as small pink macules evolving to vesicles 2
• Coxsackievirus A6 has emerged as a cause of atypical HFMD with more extensive cutaneous involvement, vesicobullous eruptions, and can affect adults in addition to children 3, 4
• Other enteroviruses (coxsackievirus and echovirus species) can cause palmoplantar involvement, though most enteroviral infections spare the palms and soles 1
• Enterovirus infections typically present with fever as the first symptom, followed by the characteristic rash distribution on hands, feet, and mouth 2

Less Common Viral Causes

• Parvovirus B19 can occasionally cause petechial rash that may involve palms 5
• Epstein-Barr virus and human herpesvirus 6 are listed among viral causes of exanthems but less commonly involve palms specifically 6

Critical Life-Threatening Differential Diagnoses

Must Exclude Immediately

• Rocky Mountain Spotted Fever (RMSF) presents with rash that progresses to maculopapular with central petechiae, spreading centripetally to involve palms and soles in approximately 50% of cases, and represents advanced disease requiring immediate doxycycline 1, 5
• Meningococcemia causes petechial or purpuric rash that can rapidly progress to purpura fulminans, typically with high fever, severe headache, and altered mental status 5
• Secondary syphilis characteristically causes maculopapular rash involving palms and soles 1, 5
• The CDC recommends assessing for life-threatening causes and initiating empiric treatment immediately if suspected, as 50% of RMSF deaths occur within 9 days and delaying treatment significantly increases mortality 1, 5

Diagnostic Approach Algorithm

Step 1: Assess for Systemic Toxicity

• Look for fever, tachycardia, confusion, hypotension, altered mental status, or rapidly progressive rash 5
• If present: Start empiric doxycycline immediately for RMSF; add ceftriaxone if meningococcemia cannot be excluded 5

Step 2: Evaluate Rash Characteristics

• Vesicular lesions on palms, soles, and mouth → strongly suggests HFMD 2
• Petechial/purpuric rash with palmar involvement → consider RMSF (especially with tick exposure history), meningococcemia, or ehrlichiosis 1, 5
• Maculopapular rash on palms and soles → consider secondary syphilis, RMSF, or atypical HFMD 1

Step 3: Consider Epidemiologic Factors

• Recent outdoor activities in grassy/wooded areas suggest RMSF or ehrlichiosis 5
• Time of year: HFMD peaks spring to fall; RMSF peaks April-September 5
• Age: Classic HFMD typically affects toddlers, but Coxsackie A6 can affect adults 3, 4
• Household contacts with similar illness suggest enteroviral transmission 4

Step 4: Laboratory Studies if Indicated

• Obtain CBC with differential, comprehensive metabolic panel, and acute serology for R. rickettsii, E. chaffeensis if RMSF or ehrlichiosis suspected 1, 5
• Blood cultures if bacterial infection suspected (but do not delay treatment) 5

Critical Pitfalls to Avoid

• Do not wait for the classic triad of fever, rash, and tick bite in RMSF, as it is present in only a minority of patients at initial presentation 5
• Do not exclude serious disease based on absence of tick exposure, as tick exposure history is present in only 60% of RMSF cases 5
• Do not exclude serious disease based on absence of rash, as up to 20% of RMSF cases and 50% of early meningococcal cases lack rash 5
• Palmar rash is not unique to HFMD and can occur in drug hypersensitivity reactions, infective endocarditis, Streptobacillus moniliformis infection, and ehrlichiosis 2
• Palmar involvement in RMSF indicates advanced disease and requires immediate treatment 5

When to Hospitalize

• Systemic toxicity present 5
• Rapidly progressive rash 5
• Diagnostic uncertainty between serious bacterial causes 5
• Generalized petechiae or purpuric rash 5