Irregularly Pigmented Hyperkeratotic Plaque on the Thumb

REPORT OF A CASE A 54-year-old black woman presented with a 30-year history of a slowly enlarging brown, hyperpigmented and hyperkeratotic plaque on her right thumb. She stated that the lesion was completely asymptomatic and was never treated. The physical examination revealed a 2×3-cm, irregularly shaped but sharply circumscribed dark-brown to tan hyperkeratotic plaque with scattered areas of hypopigmentation on the palmar surface of her right thumb ( Figure 1 ). A biopsy was performed and its histopathologic feature is shown in Figure 2 . What is your diagnosis? Submissions Clinicians, local and regional societies, and residents and fellows in dermatology are invited to submit quiz cases to this section. Cases should follow the established pattern and be submitted double-spaced and in triplicate. Photomicrographs and illustrations must be clear and submitted as positive color transparencies. If photomicrographs are not available, the actual slide from the specimen will be acceptable. Material should be accompanied