Brown plaques on the lower back.

A 12-year-old girl presented with a 2-year history of a 10 cm area of asymptomatic brown coalescent plaques of coalescent, linearly arranged papules on the lower back. No other physical or systemic abnormality was detected. Routine laboratory investigations, including thyroid function tests, were normal. The histopathological examination revealed hyperkeratosis, papillomatosis, and elongated rete ridges in the epidermis. On special staining (Alcian blue), mucin deposition was seen in the papillary dermis. The remaining dermis was normal. A diagnosis of Mucinous Nevus was made.