Hyperpigmentation in acanthosis nigricans versus that in Addison's disease

I was looking at this picture and recognized the hyperpigmentation of acanthosis nigricans, which is commonly associated with type II diabetes millitus. However, I remembered that hyperpigmentation can also be cause by Addison's disease. Should I, based on this picture alone, be able distinguish the two?

The answer is yes ... (maybe)


Acanthosis nigricans is a velvety hyperpigmentation of the skin usually found in body folds. As the name suggests, there is acanthosis, which means thickening of the stratum spinosum. In other words, it is a dark, thickened patch of skin. The most common cause is insulin resistance, which leads to increasing levels of circulating insulin. This extra insulin activates insulin-like growth factor 1 (IGF-1) leading to proliferation of keratinocytes and fibroblasts. Insulin may also stimulates melanocytes into producing melanin. The hyperkeratosis (source) and melanin production lead to hyperpigmentation. There are other causes of acanthosis nigricans, but these are rarely encountered in pediatrics.

The hyperpigmentation seen in Addison's disease is different in that it is not limited to the skin folds (although there is uneven distribution) and there is no skin thickening. This can be explained by the pathophysiology. Addison's disease is primary adrenal insufficiency. Because of the ensuing decrease in cortisol production, the hypophysis of the pituitary is stimulated. It mostly secretes ACTH (adrenocorticotropin hormone) in an attempt to get the adrenal glands pumping more cortisol. But the hypophysis often also secretes excessive melanocyte-stimulating hormone (MSH), which raises melanin levels and leads to hyperpigmentation.


Of course, a patient with primary adrenal insufficiency will present dramatically differently than one with type II diabetes, but that is a matter for another post and another day.