NUMBERS AND DIFFERENTIATION STATUS OF MELANOCYTES IN IDIOPATHIC GUTTATE HYPOMELANOSIS

The etiology and pathogenesis of idiopathic guttate hypomelanosis (IGH ) are largely unknown. To investigate whether the pathologic alteratio n in IGH involves changes in melanocytic differentiation, cell number, or both, we studied nine lesions of IGH by immunoperoxidase, using mo noclonal antibodies against the KIT receptor and a panel of melanocyte differentiation antigens (tyrosinase-related protein-1, tyrosinase, a nd gp100/pmel17). In each case, compared with grossly normal non-lesio nal skin, IGH lesions showed markedly reduced numbers both of KIT+ cel ls and of cells expressing melanocyte differentiation antigens (p < 0. 0001). Double immunofluorescence labeling of lesions revealed only sca ttered cells with a less-differentiated phenotype, i.e. cells positive for KIT but having low or undetectable TRP-I. These results indicate that the pathogenesis of IGH involves an absolute decrease in the numb er of melanocytes; a block in melanocyte differentiation does not appe ar to be a major component of the process.