Acanthosis nigricans: a flag for insulin resistance

Objectives: Acanthosis nigricans refers to the velvety, black hyperpigmentation seen in the flexures. It is a cutaneous marker for insulin resistance (IR), some metabolic disorders and rarely malignancy. When secondary to IR, it is asymptomatic, except for the hyperpigmentation. The neck is the most accessible and easiest to grade. Our aim was to identify the predictive value of the grades of acanthosis nigricans in identifying IR, the predictive value of the textures of acanthosis nigricans in identifying IR, and the diagnostic utility of acanthosis nigricans grading in comparison to the laboratory tests. Settings and subjects: The institutional ethics committee of Sri Ramachandra University approved this study. Three hundred consecutively presenting adults (50 males) with acanthosis nigricans neck were enrolled. Design: History, physical parameters and acanthosis nigricans grades, location and textures were noted. An oral glucose tolerance test (OGTT), fasting serum insulin and homeostasis model assessment of IR (HOMA IR)were carried out. The acanthosis nigricans grades were correlated to establish any association. Thirty obese controls without acanthosis nigricans were included. Outcome measures: OGTT, fasting serum insulin and HOMA IR were the outcome measures studied. Results: This cross-sectional study revealed that 94 subjects with acanthosis nigricans (31.34%) had IR. Grades III and IV, and textures II and III, were more predictive of IR. Acanthosis nigricans grading was insignificant in the non- insulin-resistant group. Acne (p-value 0.379), hirsutism (p-value 0.12) and acrochordons (p-value 0.415) were not significantly associated with IR. Conclusion: Severe grades and higher textures of acanthosis nigricans are reliable clinical diagnostic tools for IR. The absence of acanthosis nigricans was not associated with IR. Acanthosis nigricans grading is an inexpensive and non-invasive way of identifying pre-diabetes.