Routine histologic examination demonstrated a normal epidermis. In the papillary and superficial reticular dermis, increased interstitial mucin and an increased number of fibroblasts and blood vessels were seen. Thickened collagen fibers were not noted. Colloidal iron staining confirmed the abundance of mucin, and a van Gieson stain showed a decreased density of elastic fibers in the affected areas.
Mucinous nevus is an uncommon connective tissue hamartoma that is characterized by increased deposition of dermal mucin in a nevoid or linear pattern. The term was first used by Redondo Bellón et al1 to describe a brown, interscapular plaque of firm, coalescent papules that had been present in a 16-year-old girl since birth. Histopathologic examination showed an accumulation of mucin in the superficial dermis, without any other remarkable findings. Other cases of both congenital and later-onset MN have subsequently been reported.2- 6 An earlier report of “congenital mucinosis of infancy” presenting in a congenital and linear fashion may represent the same entity.7
Coalescing, Nevoid Papules in an Infant—Diagnosis. Arch Dermatol. 2005;141(7):897-902. doi:10.1001/archderm.141.7.897-d