Clinico-investigative Study of Facial Acanthosis Nigricans.

Background: Facial acanthosis nigricans (FAN) is an underrecognized and underdiagnosed entity. The typical presentation of acanthosis nigricans (AN) seen elsewhere on the body like axillae and groins is not seen on the face, making it mimic other pigmentary disorders. Moreover, FAN is seldom not accompanied with AN on the classical sites making the diagnosis challenging. The aims of this study were to determine clinical, dermoscopic, and histopathological features of FAN and to estimate the prevalence of obesity and insulin resistance (IR) in FAN.

Methods: Forty cases of FAN and forty healthy nonobese individuals with comparable ages and gender were included in the study. Body mass index, waist circumference, hip circumference, waist to hip ratio, and serum fasting lipid levels were used to evaluate obesity, whereas serum fasting insulin and Homeostatic Model of Assessment of Insulin Resistance (HOMA-IR) were used to evaluate IR. Dermoscopy was performed in all cases. Histopathological features of the skin biopsies were reviewed.

Results: Out of the 40 cases, 24 were male and 16 were female. The patterns of facial pigmentation in addition to the classic pattern were a hyperpigmented band over forehead (55%), periorbital darkening (25%), perioral (10%), and generalized darkening (10%). Dermoscopy in all cases revealed linear crista cutis, sulcus cutis, and hyperpigmented dots in crista cutis. Biopsy of 20 cases showed mild hyperkeratosis, acanthosis, papillomatosis, and increase in basal melanin. Clinico-dermoscopic-histological correlation showed that milder (light brown) variants of FAN had follicular plugging and subtle sulci pattern with irregular brown globules and perifollicular pigmentation on dermoscopy and mild hyperkeratosis and hypermelanization of the basal layer with minimal acanthosis and papillomatosis on histopathology. On the other hand, chronic variants (dark brown and black) showed prominent sulci, larger brown globules, and perifollicular hyperpigmentation on dermoscopy and moderate hyperkeratosis and hypermelanization of the basal layer with moderate to severe acanthosis and papillomatosis on histopathology. Fasting blood glucose, insulin, HOMA-IR, fasting serum triglyceride, and total cholesterol were statistically significantly high in cases in comparison with controls (-value <0.05).

Conclusions: Varied clinical presentations of FAN were observed. Dermoscopy and histopathology provide a good aid. FAN may be considered as a cutaneous marker of obesity and IR. Thus, FAN should be suspected in patients presenting with facial melanosis who are obese and have AN over other sites, although FAN can also present de novo.