Acanthosis nigricans in Obese Women with Hyperandrogenism: Characterization of an Insulin-Resistant State Distinct from the Type A and B Syndromes

Acanthosis nigricans and hyperandrogenism are commonly found in patients with extreme target cell resistance to insulin, as in the type A and B syndromes of insulin resistance. However, the significance of concurrent acanthosis nigricans and hyperandrogenism in other clinical settings is not clear. We observed acanthosis nigricans to be present in 5% (15 of 300) of patients being evaluated for hyperandrogenism, and carried out studies of insulin binding and action in a group (7) of these women. Although none were diabetic, all were insulin resistant as assessed by hyperinsulinemia when fasting and after oral glucose administration. All patients were obese (mean IBW, 169%). However, when matched to hyperandrogenized women of similar body weight, patients with acanthosis nigricans were clearly more hyperinsulinemic. Insulin binding to monocytes and red cells was decreased in patients with acanthosis, and the extent of decrease was predicted by the fasting insulin level. There was also marked resistance to exogenous insulin during euglycemic insulin clamp studies in the two patients so tested. Anti-insulin receptor antibodies were not detectable, ruling out the type B syndrome. Unlike the type A syndrome, insulin binding to monocytes of these patients increased after acute (2/2) and chronic (1/1) caloric restriction. In the latter patient, acanthosi nigricans remitted as insulin resistance and the insulin binding defect improved. We conclude that acanthosis nigricans is present in as many as 5% of women with clinically significant hyperandrogenism. These women, although not diabetic, have fairly marked insulin resistance. Despite a number of clinical similarities to patients with the type A and B syndromes, the insulin resistance of these women seems more likely to be a consequence of their obesity, and caloric restriction would appear to be the most appropriate therapy. The basis for apparent interrelationships between insulin, androgens, and acanthosis nigricans in these and other patients is discussed.