Pathologically, it is characterized by an increased number of melanocytes associated with hyperkeratotic epidermal papillomatosis.
It is strongly associated with insulin resistance but it is a non-specific condition and can also be found in obesity, polycystic ovarian syndrome, endocrine diseases like acromegaly and Cushing's syndrome, as well as some malignant tumours.
The severity of the acanthosis nigricans correlates with the degree of insulin resistance and the level of serum insulin.
The exact mechanism of its formation is still unclear but it is speculated that there are related IGF-1 receptors in the skin which are activated by ambient hyperinsulinemia.
If the insulting factor is removed, there may be a regression of the lesion.
Below are photos of a patient requiring more than 100 IU of insulin per day and despite dieting, the level of glycemia remained high.
It is an interesting case because it is an atypical location for acanthosis nigricans. The back of neck and axilla were free of any lesions.