Characteristics of Hand, Foot, and Mouth Disease (HFMD) Lesions
HFMD lesions characteristically begin as small pink macules that evolve into vesicles with a highly distinctive distribution on the palms, soles, and oral cavity, though atypical presentations with widespread involvement are increasingly recognized. 1, 2
Classic Lesion Morphology and Evolution
Skin Lesions
- Initial appearance: Small pink macules that progress to vesicular lesions surrounded by an erythematous halo 2, 3
- Vesicle characteristics: The vesicles are typically small, oval-shaped, and contain clear fluid 4
- Distribution pattern: Highly characteristic concentration on palms and soles, distinguishing HFMD from chickenpox which has widespread distribution 2
- Lesion behavior: Vesicles may rupture to form shallow erosions, particularly on pressure-bearing areas of the feet 1
Oral Lesions
- Location: Oral ulcers initially appear on the soft palate, followed by involvement of the tongue, buccal mucosa, and gingiva 3
- Appearance: Begin as small red spots that evolve into painful vesicles, which quickly rupture to form shallow ulcers with erythematous borders 1
- Timing: Oral lesions are often the first clinical manifestation, sometimes appearing before skin lesions develop 3
Atypical Presentations (Increasingly Common with Coxsackievirus A6)
Extended Distribution Patterns
- Widespread exanthema: Up to 87.6% of confirmed cases show lesions beyond the classic hand-foot-mouth distribution 4
- Common additional sites: Buttocks, legs, arms, and trunk involvement occurs frequently 4
- Severe presentations: Approximately 41.5% of cases involve 5 or more anatomical sites, classified as widespread exanthema 4
Atypical Morphologic Features
- Perioral involvement: Vesiculobullous lesions around the mouth are strongly associated with Coxsackievirus A6 infection 5, 4
- Larger bullous lesions: Some cases present with vesiculobullous exanthema rather than typical small vesicles 5
- Trunk involvement: Lesions on the trunk are considered atypical but increasingly reported 5
Key Distinguishing Features from Similar Conditions
Differential Diagnosis Considerations
- Unlike chickenpox: HFMD vesicles concentrate on distal extremities rather than being widely distributed with central predominance 2
- Unlike Kawasaki disease: HFMD presents with vesicular lesions rather than diffuse erythema, and lacks the persistent high fever typical of Kawasaki 2
- Unlike herpes simplex: HFMD has characteristic distal extremity involvement, whereas HSV typically clusters around the mouth or genitals 1
- Other conditions to consider: Rash on palms and soles can also occur in syphilis, meningococcemia, Rocky Mountain spotted fever, drug reactions, and ehrlichiosis 2
Clinical Pitfalls to Avoid
- Misdiagnosis risk: Atypical HFMD can be mistaken for chickenpox, impetigo, or vasculitis due to variable morphology 6
- Timing of diagnosis: Oral lesions may be the only initial sign, with skin lesions appearing days later or not at all 3
- Adult presentations: HFMD increasingly affects immunocompetent adults through familial transmission, not just children 5
- Seasonal variation: Atypical HFMD caused by Coxsackievirus A6 can occur in winter, unlike classic presentations 6