An 11-year-old boy presented with a rash on his back, abdomen, arms, and legs that had been present for several years. The rash was nonpruritic, but the patient experienced occasional irritation. He was previously treated with ketoconazole cream without improvement. Treatment with topical hydrocortisone and moisturizer was also ineffective. The patient's mother reported he was otherwise healthy and growing well.

Physical examination revealed well-demarcated hypopigmented macules and patches that were coalescing on his back, abdomen, buttocks, medial upper arms, and posterior thighs (Figure 1). Some of the lesions had mild erythema and over-lying scale, and a few were subtly atrophic. A hypopigmented lesion on his right posterior thigh showed erythema with over-lying scale and follicular prominence. Wood lamp evaluation showed hypopigmentation. Biopsies of two representative lesions were obtained.

QUESTION

Based on the patient's history and physical examination, which one of the following is the most likely diagnosis?

• A. Atopic dermatitis.

• B. Hypopigmented mycosis fungoides.

• C. Tinea versicolor.

• D. Vitiligo.