Lichen spinulosus. Clinicopathologic review of thirty-five cases.

Lichen spinulosus is a rare, idiopathic dermatosis characterized by follicular keratotic papules that are grouped into large patches. In this report the clinical and histologic data of 35 patients with lichen spinulosus are presented. The patients consisted of 14 males and 21 females, and their average age was 17.8 +/- 9.5 years. The average age at onset of disease was 16.2 +/- 10.1 years. Affected areas were symmetrically distributed and involved the extensor surfaces of the arms and legs, back, chest, face, and neck. Lesions were characterized by round or oval, 2 to 6 cm plaques composed of grouped punctate, "thorny," 1 to 3 mm, follicular keratotic papules. Microscopic examination revealed keratotic plugging of the follicular infundibulum and a perivascular and perifollicular mononuclear infiltrate. Although the cause is not yet known, lichen spinulosus probably represents a follicular reaction pattern of more than one origin.