Atypical presentation of acanthosis nigricans.

Sir,

We document one case of acanthosis nigricans (AN) in an atypical site.

The patient was a 48-year-old achondroplastic, diabetic male, school teacher by profession with a body mass index (BMI) of 26 kg/m2. His clinical examination revealed AN over the nape of the neck, axilla, and forehead [Figure 1]. He had normal developmental milestones, and other systemic examinations were essentially within normal limits. Laboratory investigations revealed glycosylated hemoglobin of 8.6% and dyslipidemia (total cholesterol level of 375 mg/dl, low density lipoprotein level of 195 mg/dl, triglyceride level of 180 mg/dl, and high density lipoprotein level of 36 mg/dl). There was no evidence of internal malignancy in chest radiography, abdominal ultrasound, upper gastrointestinal endoscopy, and colonoscopy.

Figure 1

Acanthosis nigricans seen on forehead

AN is a brown-to-black velvety hyperpigmentation of skin. The common sites involved are posterior and lateral folds of neck, axilla, umbilicus, and groin.[1] Forehead, oral mucosa, and eyelids are rarely involved. It may be mistaken with giant melanocytic nevus, atrophic seborrheic dermatitis, hemochromatosis, or atopic dermatitis. AN is associated with insulin resistance states like type 2 diabetes, polycystic ovarian syndrome, and obesity. Crouzon's syndrome and Costello's syndrome are also associated with AN. Severe achondroplasia with developmental delays and AN (SADDAN) have been documented.[2] As in our case, achondroplasia without the presence of developmental delays and AN have also been reported. AN is a paraneoplastic manifestation of internal malignancies of stomach, gut, ovary, prostate, and others. AN is a clinical diagnosis only rarely requiring a skin biopsy. However, a meticulous search for underlying disease and malignancy is required. Treatment of AN involves treatment of the underlying disease or tumor, avoidance of precipitating drugs like niacin, steroids, protease inhibitors, and use of topical keratinolytics, oral isotretinoin, metformin, and ultimately, cosmetic surgery.[3]