A quantitative scale of acanthosis nigricans.

Abstract

To develop and validate a scale for acanthosis nigricans (AN). Subjects were participants from the San Antonio Family Diabetes Study and the San Antonio Family Heart Study. A total of 406 subjects were independently examined for AN by at least two observers. Five locations were examined: the neck, axilla, elbows, knuckles, and knees. Interobserver concordance and kappa statistics were calculated to determine replicability of the scale. Comparisons of diabetes-related risk factors by AN score were also calculated. Only the neck had consistently high kappa statistics, and thus, other locations were excluded from further analyses. Elevated AN was strongly associated with elevated fasting insulin and BMI in both diabetic and nondiabetic subjects. Elevated AN was also strongly associated with elevated fasting glucose, systolic blood pressure, and diastolic blood pressure, and with decreased HDL in nondiabetic subjects. In diabetic subjects, elevated AN was associated with elevated total cholesterol. We have developed a scale for AN that is easy to use, has high interobserver reliability in Mexican Americans, and correlates well with fasting insulin and BMI. This scale will permit longitudinal and cross-sectional evaluation of AN and will permit the evaluation of AN as a trait in genetic studies.