A case of mucinous nevus clinically mimicking nevus lipomatosus superficialis.

Abstract

Dear Editor: Mucinous is a very rare entity and can be classified as both a cutaneous mucinosis and a connective tissue nevus1. The term nevus was proposed because of its nevoid appearance and the characteristic pattern of mucin deposits in the papillary dermis1. We report the case of a mucinous diagnosed in a young Korean man. A previously healthy 24-year-old man visited our clinic because of confluent flesh-colored to brownish non-firm nodules on his left lower back, with a zosteriform distribution (Fig. 1). The skin lesions had been present since adolescence without any symptom; however, they slowly grew in size. He had no history of trauma, and the lesion was not treated before. He also denied any familial history. Biopsy was taken, with the first impression of lipomatosus superficialis (NLS) according to clinical features. Histologically, the findings consisted of a band-like deposit of mucin mainly in the superficial dermis, with papillomatosis, hyperkeratosis, and elongation of the rete ridge in the epidermis (Fig. 2A). The mucin deposited in the dermis stained positive with alcian blue at pH 2.5 (Fig. 2B). Finally, the lesion was confirmed as a mucinous (epidermal-connective tissue of proteoglycan [epidermal-CTNP]). For the treatment, a first-stage operation was done without any complication, and a second-stage operation is planned 4 months later. Most of the lesions were removed with the first-stage operation and no recurrence has occurred. Fig. 1 Confluent flesh-colored to brownish non-firm papules and nodules on the left lower back, with a zosteriform distribution. Fig. 2 (A) The band-like deposition of mucin was mainly observed in the superficial dermis, with papillomatosis, hyperkeratosis, and elongation of the rete ridge in the epidermis (H&E, ×40). (B) Mucin deposited in the papillary dermis stained ... Mucinous is a neoplastic hamartoma and a rare form of primary cutaneous mucinosis2. Mucinous clinically presents as grouped brownish papules and confluent plaques, usually with a unilateral, linear, zosteriform, or grouped distribution. It usually appears at birth or in early childhood and mainly occurs on the back2. Although most cases are sporadic, the possibility of familial association has been suggested2. The nevoid feature of mucinous needs to be clinically differentiated from epidermal or NLS. In mucinous nevus, the band-like deposit of mucin is limited mainly in the superficial dermis, like in our case3. However, recently, a case of mucinous with mature fat cells in the upper dermis similar to NLS has been reported, making the diagnosis more confusing3. Mucinous is divided into two histopathologic types: CTNP type and combined epidermal-CTNP type4. The difference between the two types lies in whether the epidermis is normal or shows hyperkeratosis and acanthosis, with elongation of the rete ridge indicating epidermal nevus4. After reviewing the histopathologic changes of the reported cases of mucinous nevus, Chi et al.4 found that approximately half of the mucinous cases were CTNP. Here, we report a rare case of mucinous nevus, the epidermal-CTNP type, presenting similar to NLS.