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Unilateral nevoid acanthosis nigricans (UNAN) is a rare, benign, autosomal dominant form of acanthosis nigricans that manifests at birth, or during childhood or puberty. The salient features include localised distribution, benign course, lack of systemic and tumour associations, and occurrence due to somatic mosaicism of postzygotic gene mutation.1 Rare sites of involvement include the face, scalp, chest, periumbilical area2 and submammary region.3 An 18-year-old man presented with a 3-year history of asymptomatic, brownish-black raised lesions on the left side of the chest extending to the axilla and mid back. He presented no personal or family history of diabetes mellitus or any endocrinopathies. He had no history of drug use and no significant weight loss. He was of average build and non-obese (body-mass-index (BMI) 17.30 kg/m2). Mucocutaneous examination showed multiple well-defined brownish-black velvety instances of plaque varying in size from 1.5×0.3 to 10×0.7 cm over the left side of the chest, extending towards the left axilla and mid-back posteriorly (figure 1). Plasma glucose level, thyroid function test, liver and renal function tests were within normal limits. Ultrasonography of the abdomen was normal. Skin biopsy showed papillomatosis with minimal acanthosis. The stratum corneum was thickened and orthokeratotic. Papillary dermis showed moderate thickening along with sparse superficial perivascular lymphohistiocytic infiltrates (figure 2). The diagnosis of UNAN was performed clinically, confirmed by the histopathology. The patient was prescribed topical tretinoin 0.05%, counselled regarding the benign nature of the disease and is under follow-up. We conclude that as UNAN is a benign form of acanthosis nigricans, with no significant systemic associations, an overly exhaustive list of investigations need not be carried out in these patients.
Unilateral nevoid acanthosis nigricans is a rare and benign form of acanthosis nigricans inherited as autosomal dominant.
It is not associated with any endocrinopathy, drugs or internal malignancy.
Linear verrucous epidermal nevus can resemble nevoid acanthosis nigricans clinically and histopathologically.
The authors wish to thank Dr Soniya Mahajan for her contribution to writing this manuscript.
Competing interests None declared.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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