Acanthosis Nigricans – A Two-Sided Coin: Consider Metabolic Syndrome and Malignancies!

BACKGROUND: Acanthosis nigricans (AN) is acquired hyperpigmentation of the intertriginous body regions. Histologically, AN is characterised by a thickened stratum corneum and a variable amount of acanthosis. Although benign and rarely symptomatic, AN may be a red flag for underlying pathologies. CASE PRESENTATION: We analysed our patients with AN and could differentiate three different patterns, that are illustrated by one case report each. The is the benign AN associated with metabolic syndrome including obesity. The second type is the paraneoplastic AN malignancy which is associated with a wider range of malignancies. This type may occur before, after or with the clinical appearance of the malignancy. The third type is relapsing AN after complete remission. We present a patient who had a malignant AN and was treated successfully for his cancer. Years later, however, AN relapsed. In that case in association with the appearance of skin tags. Cancer restaging excluded a tumour relapse. His BMI was 31.2 kg/m(2), and the diagnosis of benign AN was confirmed. CONCLUSIONS: The diagnosis of AN remains incomplete without screening for metabolic syndrome and/ or cancer. The combination of AN and skin tags is more often associated with metabolic syndrome. AN may be considered as a red flag for malignancies and the metabolic syndrome.