Novel hyperpigmentation pathophysiology following a prolonged course of imipramine therapy

Imipramine is a tricyclic antidepressant typically reserved for patients with treatment-resistant mood disorders. A rare side effect of long-term use of imipramine is a slowly progressive melanin-associated, slate gray-blue hyperpigmentation of the skin in a photo-distributed pattern. We report a case of imipramine-induced hyperpigmentation developing 50 years after initiating imipramine therapy, whose lesions were essentially devoid of melanin on histopathological exam. This differs from all other reported cases of imipramine-induced hyperpigmentation in two notable respects. First, the time between initiating imipramine therapy and the onset of pigmentation changes was nearly 30 years longer than prior case reports. Second, the lack of melanin in our samples suggests a divergence from the hypothesized melanin-imipramine complex mechanism of hyperpigmentation. Instead, we propose a novel pathogenesis of imipramine-induced hyperpigmentation that is unrelated to melanin.