Case report: acanthosis nigricans resulting from repetitive same-site insulin injections.

Although acanthosis nigricans (AN) may be associated with internal malignancies, a benign form is more common, and a subset of these is drug-induced. In this case, a solitary, hyperpigmented, acanthotic plaque developed on the right abdomen after daily, same-site injections of insulin over a six-month period. The lesion completely resolved eight months after insulin injections were rotated to other locations. Acanthosis nigricans recurred, however, at the original location two months after the patient resumed serial same-site insulin injections, against medical advice. This provides direct evidence that localized hyperinsulinism is causally related to AN through its effect on insulin-like growth factor receptors.