Hydroxyurea-induced Tongue Hypermelanosis and Transverse Melanonychia

Hydroxyurea (HU) is a commonly used medication for myeloproliferative neoplasm (MPN) and is usually well tolerated. Cutaneous toxicity of HU is well known and can be seen in several manifestations. We report a case of a man with MPL gene mutation associated with essential thrombocytosis, who had a rare mucocutaneous toxicity with diffuse tongue, skin and nail discoloration. Mucocutaneous toxicity is usually a benign condition and self-resolves after discontinuation of the medication. It can lead to patient anxiety and medication discontinuation. The mechanism for development of HU-induced mucocutaneous hyperpigmentation is poorly understood.