Hypopigmented keratosis: is it a hyperkeratotic variant of idiopathic guttate hypomelanosis?

We have occasionally seen patients with acquired well-demarcated, scattered hypopigmented papules. In this study, we investigated the clinical and histopathological characteristics of such lesions. Biopsies were taken from the lesional and perilesional normal skin from 10 of 13 patients, which were compared with 10 idiopathic guttate hypomelanosis (IGH) samples. The lesions were scattered, well-circumscribed, flat-topped, hypopigmented papules. There was no age or gender predilection. Marked hyperkeratosis was present, with clear-cut margins distinguishable from the adjacent normal epidermis. The melanin content was decreased in the lesional epidermis, which was associated with a decrease in expression of melanogenesis-associated markers such as tyrosinase and NKI/beteb (marker of gp100) and reduction in the number of melanocytes. These histological findings were similar to those of IGH except for the additional finding of a thicker stratum corneum in this case seem to represent a 'hyperkeratotic' variant of IGH.