Investigations
Investigations to consider
fasting blood glucose
Test
Fasting blood glucose and insulin levels are checked to screen for the presence of insulin resistance in patients with acanthosis nigricans who are obese.[18]
Result
elevated
fasting blood insulin
Test
Fasting blood glucose and insulin levels are checked to screen for the presence of insulin resistance in patients with acanthosis nigricans who are obese.[18]
Result
elevated
abdominal CT
Test
May be performed as part of a thorough examination in patients with acanthosis nigricans (AN) where no other cause is identified.
Also important to search for intra-abdominal malignancy in patients who have rapid, widespread onset with involvement of mucosal surfaces and palms.[2][24]
Malignant AN may be accompanied by the sudden appearance of multiple seborrhoeic keratoses or generalised pruritus.[8]
Patients with malignant AN are thin, rather than obese, and are typically over the age of 40 years.[2][8][9]
Result
image consistent with abdominal malignancy
skin biopsy
Test
Not required in most cases.
Performed when clinical history and examination is not diagnostic.
The typical findings include epidermal acanthosis with papillomatosis and hyperkeratosis. There is usually not increased melanin production, as the dark clinical appearance is thought to be due to hyperkeratosis and papillomatosis, although a few cases may show increased intra-epidermal melanin.[2]
Findings are similar to those seen in some cases of epidermal naevus, seborrhoeic keratosis, and confluent and reticulated papillomatosis. Therefore, biopsy findings must be considered in light of clinical history and examination in order to make the most specific diagnosis.
Result
abnormal epidermal proliferation typical of acanthosis nigricans
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