Coexistence of Riehl's melanosis and lichen planus.

A 61-year-old man presented with purple-red papules and plaques. These lesions on the nape and dorsal aspects of both hands displayed the histological findings characteristic of lichen planus. Riehl's melanosis, which is synonymous with pigmented contact dermatitis, was present on the forehead and bald scalp. Riehl's melanosis typically appears on the face and is induced by cosmetics. Causative factors in this case, however, remained undefined. The coexistence of lichen planus and Riehl's melanosis at separate sites in a single patient suggests that the two diseases represent manifestations of specific immune responses characteristic of lichenoid tissue reaction and situate in the same spectrum. The differences in the skin manifestations of lichen planus and Riehl's melanosis might depend on the severity of immune responses against intrinsic or extrinsic antigens. In addition, the skin manifestations of lichenoid tissue reaction might depend on the disposition of the lesion sites.