In a 61‑year‑old man presenting with a bilateral painful rash on his feet, could this represent herpes zoster (shingles) or is another etiology more likely?

Bilateral Painful Foot Rash: Almost Certainly Not Shingles

This presentation is highly unlikely to be herpes zoster (shingles) because shingles characteristically presents as a unilateral, dermatomal rash—not bilateral involvement of both feet. 1, 2

Why This Is Not Shingles

Dermatomal Distribution Rules Out Shingles

• Shingles presents as a unilateral vesicular eruption confined to a single dermatome (the area of skin supplied by a single sensory nerve root), never bilaterally symmetric 2, 3
• A single dermatome covers only a strip or band of skin, not an entire limb or bilateral extremities 2
• The feet are innervated by multiple dermatomes (L4-S2), and bilateral involvement spanning both feet cannot be explained by reactivation of VZV in a single dorsal root ganglion 2

Disseminated Shingles Does Not Present This Way

• Even disseminated varicella-zoster virus (which occurs in 10-20% of immunocompromised patients) characteristically begins on the face and trunk, then evolves peripherally—not as isolated bilateral foot involvement 2
• Disseminated disease is defined by lesions in more than three dermatomes, visceral organ involvement, or hemorrhagic lesions—not symmetric bilateral extremity rash 1, 3

What to Consider Instead

More Likely Differential Diagnoses

• Contact dermatitis (bilateral exposure to irritant or allergen in footwear)
• Cellulitis or erysipelas (bacterial skin infection, though bilateral presentation is less common)
• Tinea pedis (athlete's foot—fungal infection commonly bilateral)
• Dyshidrotic eczema (vesicular eruption of hands/feet, often bilateral)
• Erythema multiforme (can present with bilateral symmetric involvement)
• Drug eruption (medication-related rash with bilateral distribution)

Critical Red Flags Requiring Urgent Evaluation

• Fever, systemic symptoms, or rapidly progressive rash suggests bacterial infection (cellulitis) requiring immediate antibiotics 4
• Immunocompromised status (HIV, chemotherapy, chronic steroids) increases risk of atypical infections 1, 3
• Vesicular lesions with hemorrhagic base in an immunocompromised patient could represent disseminated VZV, though bilateral foot-only distribution remains atypical 3, 5

Diagnostic Approach

Clinical Examination Priorities

• Assess for unilateral dermatomal pattern on careful inspection—if truly present, reconsider shingles 2, 3
• Examine for vesicles, pustules, or crusting to narrow the differential (vesicles suggest viral or dyshidrotic eczema; pustules suggest bacterial infection) 3
• Check for lymphadenopathy, fever, or systemic signs that indicate bacterial infection or disseminated viral disease 4, 3

When Laboratory Confirmation Is Needed

• PCR of vesicle fluid is the most sensitive test (approaching 100% sensitivity/specificity) if vesicular lesions are present and viral etiology is suspected 3
• Bacterial culture if cellulitis or impetigo is suspected 4
• KOH preparation if fungal infection (tinea pedis) is considered 4
• Tzanck smear can demonstrate multinucleated giant cells confirming herpesvirus infection, though it cannot differentiate VZV from HSV 3

Screening for Underlying Conditions

• Consider HIV testing, diabetes screening, or evaluation for occult malignancy if the patient is immunocompromised or has risk factors, as these increase susceptibility to atypical infections 3, 5

Common Pitfall to Avoid

Do not assume every painful vesicular rash in an older adult is shingles. The hallmark of herpes zoster is unilateral dermatomal distribution—bilateral symmetric involvement of both feet does not fit this pattern and requires consideration of alternative diagnoses 1, 2, 3. Misdiagnosing this presentation as shingles would delay appropriate treatment for the actual underlying condition (e.g., bacterial cellulitis requiring antibiotics, or contact dermatitis requiring topical corticosteroids).