Tyrosinase-positive melanocyte distribution and induction of pigmentation in human piebald skin.

White forelock and hypomelanotic macules of piebaldism have been revealed to have almost regularly distributed, dopa-positive melanocytes, though with lower density than normal, on separated epidermis despite previous reports describing few or no melanocytes in piebald spots. The melanocytes observed in piebald hypomelanotic spots seem to be classified into the following two types: (1) strongly dopa-positive and markedly hyperdendritic large cell type and (2) moderately dopa-positive and slightly hyperdendritic, oversized cell type. The former are primarily seen in hypomelanotic lesions, while the latter are seen in transitional lesions. The above difference seems to be associated with compensatory melanogenic function of melanocytes in vivo. Moreover, we have induced new hyperpigmented spots in hypomelanotic lesions, with the exception of white forelock, following therapy with oral methoxsalen plus ultraviolet A light.