Lichen planus pigmentosus-inversus: case report and review of an unusual entity.

Lichen planus pigmentosus-inversus is a rare variant of lichen planus, with less than 20 cases reported in the medical literature. It presents as asymptomatic to mildly pruritic, hyperpigmented macules and/or patches involving intertriginous and flexural areas and skin folds in light-skinned individuals. The unique pattern of skin involvement, clinical features, and histology are distinctive. The combination of hyperpigmented lesion(s) isolated to non-sun exposed, intertriginous, and flexural areas with lichenoid histology is unique and separates it from other similar entities, such as lichen planus actinus and erythema dyschromicum perstans/ashy dermatosis. The case well highlights this unusual condition and represents the first case reported in the United States.