Acanthosis Nigricans

Key Points
Brown to black, poorly defined, velvety hyperpigmentation of the skin
Typically found in body folds or creases like the armpits, groin, or neck
Could be genetic in nature, but is often associated with obesity.

Acanthosis nigricans is a skin disorder characterized by dark, thick, velvety skin in body folds and creases. It appears slowly and doesn’t cause any symptoms other than skin changes. Typically, it occurs in people under the age of 40. It’s perhaps genetic in nature, but often associated with obesity, and the hyperpigmentation often occurs in body folds or creases, such as the armpits, groin or neck, although it can also occur in the lips, palms, soles of feet, or other areas.

The most common cause of Acanthosis nigricans is insulin resistance — which leads to increased circulating insulin levels — as a result of Type 2 diabetes or obesity. Eating too many starches or sugars can also lead to raised insulin levels, which can result in the skin disease. It is also common with people of African descent. Further, it can be caused by certain medications, such as glucocorticoids, niacin, insulin, oral contraceptives, or protease inhibitors.

Differential Diagnosis (Other conditions with similar appearance)
Atopic Dermatitis
Becker nevus
Candidiasis
Erythrasma
Giant melanocytic nevi
Hypertrophic seborrheic keratosis
Linear epidermal nevus
Pemphigus vegetans

Diagnosis
Key Points
Diagnosis based on the characteristic appearance of the affected area
Skin Biopsy may be performed to rule out other conditions

Acanthosis nigricans is typically diagnosed based on the characteristic appearance of the affected area. A skin Biopsy may be performed to rule out similar appearing conditions.

Treatment
No treatment is necessary, though it is important to treat the underlying cause

Acanthosis nigricans usually only causes changes to the appearance of the skin, so no particular treatment is needed. However, it is important to treat the underlying cause, whether it be obesity or raised insulin levels. People with Acanthosis nigricans should be screened for diabetes or, in some cases, cancer. Controlling blood glucose levels through exercise and diet often should improve symptoms. Other treatments, which have proven minimally effective, may include Retin-A, 20% Urea, alpha hydroxyacids, and salicylic acid prescriptions. Acanthosis nigricans often fades if the underlying cause can be determined and treated appropriately.