Mucinous nevus is a rare entity characterized by mucin deposition in the papillary dermis. Herein we present a case and review the available literature.
A man in his 50s presented to clinic for a second opinion regarding asymptomatic, grouped, skin-colored papules on his left chest present since his earliest memory (Figure, A). He denied a family history of similar lesions. A biopsy had previously been performed, and the findings were initially interpreted as indicating focal cutaneous mucinosis. Review of the biopsy specimens revealed loosely separated collagen fibers in the papillary dermis with increased mucinous ground substance (Figure, B). In addition, occasional stellate fibroblasts were noted. Considering the clinical and pathologic findings together, a diagnosis of mucinous nevi was rendered.
A, In the clinical presentation, grouped skin-colored papules are evident on the left chest. B, The biopsy specimen shows increased mucinous ground substance in the papillary dermis and mild rete ridge elongation (hematoxylin-eosin, original magnification ×200).
Mucinous nevi typically present as brownish papules and plaques arranged in a unilateral, linear, grouped, or dermatomal distribution. The Table summarizes the clinical findings from 22 reported cases in the literature, including the present case. Seventy-one percent of cases were reported in men, and the most common location was the back.1- 4 Of note, 45% of cases were reported in Asian countries. Half of all cases were present at birth, while the remainder developed in childhood, adolescence, or early adulthood.5
The primary histopathologic feature of mucinous nevi is a diffuse, bandlike deposition of mucin in the superficial dermis with a scarce cellular component composed of spindle cells.5 Historically, there has been debate over the classification of mucinous nevi, with some researchers classifying it as a form of primary cutaneous mucinosis, while others classify these cases as connective tissue nevi.3
Those who support the connective tissue origin will further divide mucinous nevi into 2 histopathologic types: a connective tissue nevus of the proteoglycan (CTNP) type and combined epidermal-CTNP type.1 In CTNP, the epidermis is normal, while in epidermal-CTNP, the epidermis shows hyperkeratosis and acanthosis with elongation of the rete ridges consistent with an epidermal nevus.1 Regardless of classification, the origin of increased mucin is unclear. Although mucin is synthesized by fibroblasts, previous studies have shown only a slight increase in activated fibroblasts. Thus, some have postulated that the upregulation of fibroblasts is responsible for the increased mucin.3
Clinically, these lesions can be hard to distinguish from connective tissue nevi such as collagenomas or elastomas. Histologic examination is essential to exclude these entities, which can be associated with congenital abnormalities. The microscopic differential diagnosis is narrow and includes focal cutaneous mucinosis and lichen myxedematosus, both of which have distinct clinical presentations. Lesions of focal cutaneous mucinosis are usually solitary papules and can be found anywhere on the body. Lichen myxedematosus presents with a slow onset of asymptomatic or slightly pruritic papules, which can be generalized or localized. Generalized subtypes of lichen myxedematosus have an associated monoclonal gammopathy, while discrete papular lichen myxedematosus, a variant of the localized subtype, has been associated with human immunodeficiency virus disease.6 Other histologic mimics, like self-healing papular mucinosis and acral persistent papular mucinosis, are easily excluded with clinical information. In our case, clinical correlation confirmed the rare diagnosis of mucinous nevus.
Treatment for a mucinous nevus is not required owing to its benign nature. Surgical intervention may remove the lesion, but scarring will result.
Corresponding Author: William James, MD, Department of Dermatology, Perelman School of Medicine, 2 Maloney Bldg, 3600 Spruce St, Philadelphia, PA 19104 (William.email@example.com).
Published Online: July 16, 2014. doi:10.1001/jamadermatol.2013.9451.
Conflict of Interest Disclosures: None reported.
Cobos G, Braunstein I, Abuabara K, Chu EY, James W. Mucinous NevusReport of a Case and Review of the Literature. JAMA Dermatol. 2014;150(9):1018-1019. doi:10.1001/jamadermatol.2013.9451