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Obesity brings with it a myriad of problems, and the skin is not spared. There are many causes for hyperpigmentation, or excessive darkening of the skin. Today we discuss one in particular that is becoming increasingly common: acanthosis nigricans (AN): more specifically: obesity-related AN (because there are other types of AN).
The skin lesions are dark and velvety to the touch with the occasional presence of skin tags. AN affects the cheeks, the nape of the neck, and other flexural surfaces (the armpits, the groin, under the breasts), and skin folds (the eyelids, the knuckles).
AN is actually divided into a few subtypes depending on its cause. All types of AN show the same skin manifestations, but the degree of these manifestations differs in each subtype.
In all types of AN, the epidermis becomes thickened, which causes the skin to be hyperpigmented. The darkening is caused by the thickness of the skin, not an excessive production of melanin.
What causes the thickening of the epidermis? Excessive skin cell proliferation, due to excessive stimulation by growth factors: specifically, insulin.
Why insulin? Because it is elevated in obesity.
Why is it elevated? There are many reasons why insulin can be elevated. In obesity, the various body cells become resistant to insulin, which makes the pancreas think there isn’t enough insulin circulating out there, so it produces more. The body then ends up with a lot of insulin that it is not using properly, so it starts using it improperly, which leads to things like hyperproliferation of the skin cells and AN.
Obesity – related AN (formerly known as pseudo AN) is the most common type of AN, and it also shows the mildest manifestations. Compared to other types of AN, lesions here are not as dark, not as thick or velvety, and not as wide spread.
Other types of AN can be associated with tumors or various endocrine diseases, or they can be familial or related to the intake of certain medications. Obesity related AN is NOT associated with malignancies.
How common is it?
AN affects more than half of the obese population. It is seen more commonly in those with darker skin tones: African Americans, Middle Easterners, Hispanics, and Asians. What’s more, it is increasingly seen in children, accompanying the rise in childhood obesity in recent years.
Is it dangerous?
Obesity – related AN is mainly bothersome cosmetically, especially if the lesions affect the face or the nape of the neck.
The significance of AN is that it is a strong indicator of a predisposition to diabetes. Patients with AN are also at an increased risk of atherosclerosis and heart disease.
How is it treated?
Simple, yet requiring so much well power: treat the underlying cause, namely: obesity.
Using peels and lightening agents and laser can give some improvement, but it is usually not satisfactory. After all, these methods do not treat the cause (insulin resistance and excessive proliferation of skin cells).
So the treatment plan would consist of a balanced diet, exercise, and doing the blood work necessary to rule out diabetes or pre-diabetes. Your doctor might also suggest the use of relevant medications such as metformin (glucophage).
With the rising prevalence of obesity, AN is being seen more often. It is understandable that the lesions themselves are the reason why many suffers from AN first visit the dermatologist. But the truth of the matter is, your doctor views AN as an indication to veer you towards a dietitian who will help you take control of your blood sugar levels before it is too late.
Thank you for reading!
WD. James et al. Andrew’s Diseases of the Skin: Clinical Dermatology 2006. Tenth Edition. Saunders Elsevier: 506-8.
WJ. Brickman et al. Acanthosis Nigricans Identifies Youth at High Risk for Metabolic Abnormalities. The Journal of Pediatrics 2010; 156 (1): 87-92.
A. Scheen et al. Acanthosis Nigricans associated with Insulin Resistance: Pathophysiology and Management. American Journal of Clinical Dermatology 2004; 5 (3): 199-203.