Ultrastructural study of two patients with both piebaldism and neurofibromatosis 1.

Piebaldism was associated with neurofibromatosis 1 (NF-1) in two patients, an association not previously reported. Dopa staining (tyrosinase) and electron microscopy were performed: no melanocytes or melanosomes were found in hypomelanotic skin of patient 2 and in the white forelock skin of patient 1; in patient 2, normal melanocytes and melanosomes were present in the white forelock epidermis but absent from the cortex, cuticles, and inner root sheath of the white forelock hair. Because these structures receive melanosomes from melanocytes in the hair bulb, it was assumed that there were no melanocytes in the hair matrix. Melanocytes and melanosomes were normal by ultrastructural criteria and in terms of their distribution in a normally pigmented macule within a hypomelanotic patch of patient 2. These and earlier report findings led to three conclusions: subtypes of piebaldism exist, including our patients showing a combination of piebaldism and NF-1; the most commonly reported subtype has no melanocytes in the white forelock and hypomelanotic skin, although microscopic islands of melanocytes may exist within hypomelanotic skin; and the ultrastructure of white forelock skin and hair of patient 2 is consistent with a mouse model of piebaldism, in which the hair follicle has no active melanocytes, but the interfollicular epidermis is normally melanized.