Insulin resistance (IR) precedes the diagnosis of many metabolic and non-metabolic illnesses, including type 2 diabetes. Acanthosis nigricans (AN) is a clinical sign associated to IR. However, AN prevalence and diagnostic accuracy in middle-age adults before or at the time of prediabetes/diabetes diagnosis remains uncertain.With the aim to define AN prevalence and diagnostic accuracy, adults between 40 and 60 years of age were consecutively invited to participate in the study. Participants were categorized into one of two main groups: individuals with normoglycemia (group 1) and hyperglycemia (group 2 [i.e., prediabetes/diabetes]). Demographic, clinical, anthropometric characteristics, HOMA-IR, HOMA-β, as well as the presence of AN on the neck, axillae, elbows and knuckles were assessed.A total of 320 consecutive participants with a mean age of 49.3 years (59.4% women) were included. Overall, AN prevalence was 46.3% while AN in group 1 and group 2, was 36.3% and 49.6%, respectively (P= 0.04). The most common affected sites in group 1 (n=80) were the knuckles (21.2%) and the neck (17.5%), while in group 2 (n= 240), the neck (29.6%) followed by the knuckles (26.7%). The specificity and positive predictive value of AN for IR were 0.85 and 0.86 in group 1 and 0.90 and 0.96 in group 2, respectively.In middle-age adults, within the entire spectrum of carbohydrate tolerance, AN is highly prevalent and specific. This finding supports its assessment as a reliable and convenient clinical sign of IR. The understanding of AN behavior through different carbohydrate tolerance strata, and its different locations, could lead to early detection of individuals at high-metabolic risk or help direct a more pathophysiological treatment approach in patients with type 2 diabetes.
