Nigricans

Acanthosis nigricans, sometimes referred to by the shorthand nigricans, is a dermatologic condition characterized by patches of dark, velvety thickening of the skin. The changes most often occur in intertriginous areas such as the back of the neck, armpits, groin, and other folds, but they can appear in other locations. The term nigricans is Latin for becoming black.

Epidemiology and associations: Acanthosis nigricans can affect people of all ages but is more common in those with obesity and insulin resistance or type 2 diabetes. It can be familial or associated with endocrine disorders such as Cushing’s syndrome, polycystic ovary syndrome, thyroid disease, and rarely with medications. A malignant form, known as malignant acanthosis nigricans, is a paraneoplastic sign linked to various cancers and may indicate an underlying malignancy.

Pathophysiology: The exact mechanism is not fully understood. Hyperinsulinemia is believed to stimulate keratinocytes and dermal fibroblasts via insulin-like growth factor receptors, promoting epidermal thickening and hyperpigmentation.

Diagnosis and management: Diagnosis is typically clinical. Evaluation often includes screening for insulin resistance, diabetes, metabolic syndrome, and other endocrine disorders; in adults with abrupt onset or extensive involvement, evaluation for an occult malignancy may be indicated. Management focuses on treating the underlying condition. Weight loss and improved glycemic control can reduce or reverse lesions. Topical therapies such as keratolytics, retinoids, or calcitriol can improve texture and appearance; laser or other dermatologic procedures may be considered for persistent symptoms.

Prognosis: Lesions may improve with treatment of the underlying disorder, particularly insulin resistance; malignant acanthosis nigricans requires management of the associated cancer and has implications for prognosis.