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84-Year-Old Female with Rash on Left Foot

Can you diagnose this case?

David L. Kaplan, MD

Signs and Symptoms

An 84-year-old woman noted this rash of 5 months’ duration on only her left foot. She had been treating the rash with tolnaftate for more than a month without improvement. Her health was otherwise good.

What is responsible for this unilateral foot rash?

Choose one to reveal diagnosis and discussion

Tinea pedis
Leukocytoclastic vasculitis
Contact dermatitis
Stasis dermatitis

Answer: Tinea pedis

See the full case at Consultant360

A potassium hydroxide (KOH) wet-mount examination of skin scrapings revealed a dermatophyte infection, confirming the clinical suspicion of tinea pedis. Involvement of the toes can be seen in the photograph, and upon close inspection, scale is visible around the erythematous spots.

Leukocytoclastic vasculitis would be unusual but is possible on the dorsum of the foot, although scale is not a feature of the condition. Contact dermatitis is a possibility in that location, necessitating the KOH examination. Psoriasis on the dorsum of one foot in an 84-year-old person would be unusual and would be ruled out by the KOH examination results. Stasis dermatitis would be expected to occur in the setting of swelling, which is absent in this case.