Can you describe the characteristic rash of hand‑foot‑and‑mouth disease, including its appearance, distribution, and typical course?

Hand-Foot-and-Mouth Disease: Characteristic Rash Description

Hand-foot-and-mouth disease (HFMD) classically presents with vesicles or erosions on the oral mucosa, hands, feet, and sometimes buttocks, but the dermatological spectrum now ranges from this traditional pattern to widespread vesicular exanthema involving five or more anatomical sites. 1

Classic Presentation

• The traditional rash consists of vesicles or erosions affecting the oral mucosa, palms, soles, and buttocks in children with acute febrile illness. 1
• Oral enanthema appears alongside a macular, maculopapular, or vesicular rash on the hands and feet. 2
• The illness is typically preceded by malaise and fever before the characteristic vesicles develop. 3

Atypical and Widespread Patterns

• 87.6% of confirmed HFMD cases now present with skin lesions extending beyond the classic hand-foot-mouth distribution, involving sites such as the trunk, arms, legs, and buttocks. 1
• 41.5% of patients develop widespread exanthema affecting five or more anatomical sites (hands, feet, mouth, buttocks, legs, arms, and trunk). 1
• Atypical presentations include peri-oral rash (strongly associated with Coxsackievirus A6), rashes on earlobes and faces, and large vesicles or bullae (≥1 cm diameter) on the trunk and bilateral limbs. 1, 4
• Coxsackievirus A6 infections cause bullous lesions in 54% of cases, compared to only 25% in non-CVA6 infections. 4

Morphology and Evolution

• Lesions may present as maculopapular rashes, vesicles, or large bullae depending on the causative serotype. 1, 4
• Hyperpigmentation develops as bullous lesions crust and heal, providing a clue to recent HFMD in patients presenting late. 4
• The rash morphology varies from Gianotti-Crosti-like eruptions, eczema coxsackium, petechial/purpuric eruptions, to vesiculobullous exanthema in atypical CVA6 infections. 5

Distribution Patterns by Serotype

• Coxsackievirus A6 is strongly associated with peri-oral rash (P < 0.001), widespread distribution, and bullous lesions. 1, 4
• Coxsackievirus A16 and Enterovirus 71 typically cause the classic hand-foot-mouth pattern, though generalized exanthema can occur with both. 1
• Both CVA6 and CVA16 can produce widespread vesicular exanthema, making serotype prediction based solely on distribution unreliable. 1

Late Complications

• Onychomadesis (nail matrix arrest and subsequent nail shedding) occurs as a late postinfectious sequela, typically developing 2–8 weeks after the acute illness. 3
• Transverse nail grooves may appear weeks after resolution of the acute rash. 3

Critical Diagnostic Pitfalls

• Do not exclude HFMD based on absence of classic hand-foot-mouth involvement—the majority of current cases present with atypical or widespread distribution. 1
• Atypical HFMD may mimic eczema herpeticum, varicella, disseminated zoster, or erythema multiforme major, requiring careful clinical differentiation. 5
• Bullous, vesicular presentations are consistent with HFMD (unlike Kawasaki disease, where such lesions should prompt alternative diagnosis). 6, 4
• Adults can develop HFMD with various clinical presentations, creating diagnostic complexity when the classic pediatric pattern is expected. 2