Acanthosis Nigricans in the Knuckles of Infants: A Novel Clinical Marker of High Metabolic Risk

INTRODUCTION: Acanthosis nigricans (AN) is an early clinical sign of insulin resistance (IR) primarily in adults. The prevalence and association of AN and IR in infants, however, remains uncertain. We aimed to describe the prevalence of AN and its association with IR in a group of Latin-American infants. METHODS: We studied a random sample of 227 healthy infants between 9 and 24 months of age. After a complete clinical history was obtained and a physical examination was performed, fasting plasma glucose and serum insulin were measured. Three blinded evaluators assessed AN in each patient. Infants with AN were categorized as cases. The HOMA-IR index cutoffs of ≥ 90th and ≥ 95th percentiles were considered IR. RESULTS: There were 49 infants with AN (21.6%) (cases) and 178 without AN (78.4%) (controls). Cases had a significantly higher mean serum insulin, fasting plasma glucose, and HOMA-IR levels of 3.67 ± 2.56 µU/ml vs. 2.42 ± 1.45 µU/ml, P = 0.005; 84.2 ± 12.6 mg/dL vs. 77 ± SD 9.9 mg/dL, P ≤ 0.001; HOMA-IR 0.77 ± 0.54 vs. 0.46 ± 0.28, P ≤ 0.001, respectively. More cases than controls presented HOMA-IR levels ≥ 95th percentile (cases 18.4%; controls 0.5%, P ≤ 0.001) and ≥ 90th percentile (cases 32.7%; controls 1.6%, P ≤ 0.001). AN in the knuckles had a high sensitivity and a negative predictive value (NPV) for detecting patients with HOMA-IR levels above the 95th percentile (sensitivity 90%; NPV 99.4%) and above the 90th percentile (sensitivity 84.2%; NPV 98.3%). CONCLUSION: AN in the knuckles is a prevalent, non-invasive, costless, and reliable screening clinical tool that can be used for early detection of infants with IR and a high metabolic risk.