Abstract

Mucinous nevus is a rare, benign, hamartomatous, entity that presents as asymptomatic, grouped papules that coalesce into plaques or as plaques in a unilateral or zosteriform distribution. We report a case of a 76-year-old male presented to the dermatology clinic for a long-standing, asymptomatic, abdominal lesion that was enlarging.  The lesion was a hyperpigmented plaque with scale and homogenous dark brown pigment that measured approximately 6 cms.  His past medical history was non-contributory. The clinical differential diagnosis included lichen simplex chronicus, seborrheic keratosis, and atypical nevus. A biopsy was taken. Histopathology showed epidermal hyperplasia with lengthened rete ridges and marked papillary dermal/superficial dermal mucin deposition. An Alcian blue stain and colloidal iron stain confirmed dermal mucin deposition. The combined findings were consistent with mucinous nevus. Mucinous nevus (nevus mucinosis) presents in childhood/young adults and more commonly occurs in men (5:1). It may be considered a form of cutaneous mucinosis or an epidermal nevus.  Pathology shows papillary dermal mucin deposition and may show epidermal hyperplasia. The histopathologic differential diagnosis includes epidermal nevus, focal cutaneous mucinosis, and papular mucinosis. The lesions can be categorized based on epidermal changes as either connective tissue nevi of proteoglycan (CTNP) type or combined epidermal-CTNP type. Given the epidermal findings in this case, it was best classified as a variant of epidermal nevus. As it is a benign entity, there is no definitive treatment. Cosmetic treatments such as surgical excision, scalpel dermabrasion, and carbon dioxide laser treatment can be performed but scarring is likely to occur.