Hypohidrosis and metal allergy: Trigger factors for unilateral lichen planus.

Unilateral lichen planus (LP) is a rare clinical variant of LP. The etiology of unilateral LP has not been clarified, although various causes have been reported because of the characteristic distribution. We focused on the contribution of metal allergy and sweating in the development of unilateral LP in this case. To confirm the presence of metal allergy, patch tests with metal allergens were performed. To investigate the cause of the unilateral distribution in unilateral LP, the function of sweating and sweat leaking in the dermis was assessed by a thermoregulatory sweat test and immunohistochemical staining of dermcidin. The patch tests with SnCl , H PtCl , ZnCl and MnCl were positive. The thermoregulatory sweat test using the starch-iodine method (Minor test) with sweating provoked by heat stimulation revealed hypohidrosis of the affected area, whereas no skin lesions were observed on the dorsal hand and wrist where sweating was normal. Histopathological examination showed keratin plugging of the acrosyringium and lymphocytic infiltrations in the papillary and subpapillary dermis around the intraepidermal and intradermal eccrine duct in the affected area. The immunohistochemical staining of dermcidin confirmed sweat leakage in the subpapillary dermis in the affected area. The symptoms refractory to the topical steroids were markedly improved after removal of the dental metals. The coexistence of metal allergy and sweat leakage in the hypohidrotic area may be involved in the development of unilateral LP.