ABSENCE OF ACANTHOSIS NIGRICANS IN A PATIENT WITH THE TYPE-B SYNDROMEOF INSULIN-RESISTANCE AND PREEXISTING DIABETES

Acanthosis nigricans is a skin lesion characterized by brown velvety h yperkeratotic plaques most often found in the axillae, the back of the neck, and other flexure areas (1). Histologically, prominent hyperker atosis, epidermal papillomatosis, and infiltration of the dermis with glycosaminoglycans are present. Acanthosis nigricans is seen in a vari ety of insulin-resistant states, such as type A and type B syndromes o f insulin resistance, polycystic overy syndrome, and obesity (2-4). Th e cause of acanthosis nigricans in insulin-resistant states is unknown , but it is thought to be caused by the stimulation of either insulin receptors or type I insulin-like growth factor receptors on epidermal and melatonin-containing cutaneous cells by high circulating concentra tions of insulin (2). Acanthosis nigricans is uniformly seen in the ty pe B syndrome of insulin resistance, which is characterized by the pre sence of anti-insulin receptor antibodies (5). We recently observed a patient with type B insulin resistance and preexisting NIDDM in whom a canthosis nigricans was absent.