Actinic keratosis recognized as a depigmented patch

We report a case of erythema with a depigmented patch on the right index finger of a 73-year-old woman. Histologically, a very small amount of melanin was found in both parts of the lesion, but a few pigment-blockade melanocytes were observed in the epidermis, and several melanophages in the dermis, of the area of erythema. On electron microscopy, a few melanosomes were present in the keratinocytes in both parts of the lesion. Since, in the erythematous area, the small blood vessels were increased in number and in size, and an inflammatory infiltration of numerous lymphocytes was present in the dermis. causing the redness, we concluded that depigmentation is probably an early clinical feature of actinic keratosis. The depigmentation may have resulted from replacement of the melanocytes by atypical cells, or from a disorder of the melanosome-melanin transmission to the keratinocytes due to the proliferation of abnormal keratinocytes in actinic keratosis, as occurs in extramammary Paget's disease.