Hyperpigmented Plaque on the Neck of a Young Female: Rare Presentation of a Common Disease

CLINICAL SCENARIO

We bring forth to your notice the case of a 16-year-old girl with a body mass index (BMI) of 19.6 kg/m², who presented to us with an asymptomatic localised darkening of skin over the front of the neck for 6 years, which started as a small, elevated dark lesion that gradually increased to its current size over the past 6 years. On examination, there were well-defined, hyperpigmented brownish-black papules coalescing to form a plaque with irregular borders and a velvety appearance over the anterior aspect of the neck around the midline, measuring approximately 8 cm × 5 cm in size. [Figure 1] There were no such lesions over other sites of the body, and the mucous membranes, hair, and nails were normal on examination. The patient had no other comorbidities. Fasting and post-prandial blood sugar levels were measured, which were within normal limits; HbA1c was 4%. Ultrasonography of the abdomen and pelvis was done, which revealed no abnormalities. A biopsy was sent from the lesion, which showed hyperkeratosis, papillomatosis, mild acanthosis, and pigmented basal layer in the epidermis with sparse lymphocytic infiltrate in the papillary dermis [Figure 2].

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Figure 1:

A 16-year-old female with multiple well-defined hyperpigmented papules coalescing to form a plaque present over the midline.

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Figure 2:

Histopathological image showing hyperkeratosis, mild acanthosis, and papillomatosis. (Haematoxylin and eosin stain 10x).

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WHAT IS YOUR DIAGNOSIS?/WHAT WOULD BE THE TREATMENT OF CHOICE?

Answer

The biopsy findings were suggestive of acanthosis nigricans.

A final diagnosis of naevoid acanthosis nigricans or rounded and velvety epidermal naevus (RAVEN) was made.

The patient was treated with 0.04% tretinoin microsphere gel and mometasone furoate cream 0.1% for application once daily and showed almost complete resolution of the lesion over 4 weeks [Figure 3].

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Figure 3:

Near complete resolution of lesion after four weeks of treatment.

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DISCUSSION

Acanthosis nigricans (AN) is a cutaneous disorder of different aetiologies, characterised by symmetric, dark, thickened, velvety appearing plaques commonly distributed in the flexures. It can also occur in the mucosae. Unilateral Naevoid acanthosis nigricans, also known as RAVEN, is a benign variant of AN occurring over a localised area that is common in children. It is not associated with any endocrine anomalies, obesity, or malignancy.^[1] It has been reported to be associated with post-zygotic gain of function mutations in fibroblast growth factor receptor 2 (FGFR2) and fibroblast growth factor receptor 3 (FGFR3), which code for tyrosine kinase receptors.^[2,3]

Various treatment modalities have been tried to treat naevoid acanthosis nigricans, including topical retinoids, CO₂ laser, calcipotriol, and a combination of ketoconazole and urea.^[1]