Acanthosis nigricans: a new cutaneous sign in severe atopic dermatitis and Down syndrome.

Acanthosis nigricans (AN) occurs associated with many different systemic diseases, such as endocrine disorders and internal malignant neoplasms. To our knowledge, the association of AN with severe atopic dermatitis (AD) or Down syndrome has not been described before. This 82-month retrospective study included 1038 patients: AN was present in 4.9% of atopic patients and 50.9% of subjects with Down syndrome. AN was more frequent in patients with severe AD and in 100% of cases of hand dermatitis and juvenile plantar dermatosis, located on the interphalangeal and metacarpophalangeal joints, whereas in Down syndrome other flexures were also affected. The pathogenesis of AN in AD is unknown, but in Down syndrome it seems to be related to obesity. Possible insulin resistance underlyng the pathogenesis of AN in these patients is still unknown.