What is the cause of this patient’s left inguinal crease rash?

A 68-year-old male presented for evaluation of a unilateral, itchy eruption confined to the left inguinal crease only. He has not changed any medications for cholesterol or hypertension.

What is the cause of his itchy eruption?

A. Tinea infection

B. Psoriasis

C. Lichen planus

D. Seborrhea

E. Candidiasis

(Answer and discussion on next page)

Answer: Annular lichen planus

A biopsy showed changes to support the diagnoses of annular lichen planus. This appearance is a long-recognized clinical variant of lichen planus, but is often considered uncommon. This patient responded to combination of naftifine gel and hydrocortisone butyrate lotion.

Tinea and Candida infection should be ruled out (which it was by potassium hydroxide test and biopsy). Seborrhea and psoriasis would be expected to have more scale and annular lesions would be possible requiring biopsy if the diagnosis was uncertain. Unilateral disease would be rare.

Reference:

Reich HL, Nguyen JT, James WD. Annular lichen planus: a case series of 20 patients. J Am Acad Dermatol. 2004;50(4):595-599.