On the nature of idiopathic guttate hypomelanosis

Clinical and morphologic studies were made of 20 cases of guttate hypomelanosis. The sharply demarcated hypopigmented macules were present on both covered and exposed sites, excluding sunlight exposure as a cause. Skin surface replicas and biopsies showed no evidence of post-traumatic or post-inflammatory scarring. The stratum corneum had fewer cell layers, but no abnormalities of keratinization were observed. Light and electron-microscopic and histochemical studies showed only reduced numbers of hypoactive melanocytes. In no case were melanocytes completely absent, excluding vitiligo. Guttate hypomelanosis is a common disorder of unknown origin. The evidence indicates an age-related somatic mutation of melanocytes.