Hypopigmented Mycosis Fungoides Mimicking Vitiligo.

Hypopigmented mycosis fungoides (HMF) is a clinical variant of MF with a presentation similar to other hypopigmented diseases, especially vitiligo. In this article, we report an adult case of HMF mimicking vitiligo. A 53-year-old man presented with an asymptomatic well-defined focal and hypopigmented patch with erythematous to brownish macules on the flank which had been developing over several months without other cutaneous findings. He had no past medical or trauma history. Skin biopsy from the hypopigmented patch indicated a slightly band-like, superficial dermal infiltrate of lymphocytes with mild cytologic atypia and epidermotropism. Fontana-Masson and Mart-1 stains showed a decrease in the epidermal pigment and the number of basal melanocytes. In addition, CD4 and CD8 stains were positive, predominantly the CD8 stain, and loss of CD7 stain was noted in the epidermal atypical lymphocytes. A T-cell receptor gene rearrangement study from the hyperpigmented area showed monoclonality. Finally, we diagnosed the patient with HMF. After about 17 months of treatment with narrow-band ultraviolet B, the hypopigmented lesion had notably improved in both the clinical and histological aspects. The clinical appearance of our case was similar to vitiligo while clinical improvement was also exceptionally similar to the skin findings from follicular repigmentation after narrow-band ultraviolet B treatment in vitiligo. Therefore, dermatologists should consider the clinical differential diagnosis of HMF in patients with an asymptomatic hypopigmentation, especially in dark-skinned Asian patients.