Mucinous nevus.

A 15-year-old boy first noticed multiple firm papules on his right upper chest two years before presenting to our clinic. These papules were densely distributed and showed epidermal nevus-like linear arrangement at some sites. The number, size, and distribution of these papules remained unchanged for one year of our observation. The papules flattened leaving scars and did not recur within a year after one shaving abrasion using a scalpel. Histopathologically, epidermis of the papule displayed acanthosis with elongated rete ridges. Accumulation of mucin was apparent in the papillary and subpapillary dermis. In mucinous nevus, the origin of cells with nevoid proliferation is obscure. In contrast with common collagenous connective tissue nevus, it is hard to define the localized persistent mucin accumulation as a nevoid manifestation. The present case of mucinous nevus might be caused by significantly stimulated glycosaminoglycan synthesis in a kind of epidermal nevus without extreme hyperkeratosis.