Photos and notes from – dermnet –
Photos and notes from – dermnet –
Acanthosis nigricans is a skin disorder characterised by darkening (hyperpigmentation) and thickening (hyperkeratosis) of the skin, occurring mainly in the folds of the skin in the armpit (axilla), groin and back of the neck.
It is usually symmetrically distributed, on the axillae, groin, neck and cubital and popliteal fossae.
Acanthosis nigricans lesions may also appear on the mucous membranes of the oral cavity, nasal and laryngeal mucosa and oesophagus.
Multiple skin tags are common.
Acanthosis nigricans is not a skin disease per se but a cutaneous sign of an underlying condition or disease.
There are two important types of acanthosis: Benign and Malignant. 
Benign types, sometimes described as ‘pseudoacanthosis nigricans’ are much more common.
The most common cause of acanthosis nigricans is insulin resistance associated with obesity. The condition can also be associated with some rare genetic disorders.
Although classically described as a sign of internal malignancy, this is very rare. 
When associated with malignancy, It can affect the mucosal surfaces and the back of the hands and the feet.
Further, when associated with malignancy, Pruritus (itching) may be present (paraneoplastic pruritus).
Patients with malignant acanthosis nigricans tend to be “middle-aged, not obese and lesions develop abruptly”.
It is very important to differentiate acanthosis nigricans related to malignancy from that related to benign conditions.
Tumours in malignant acanthosis nigricans are usually very aggressive and spread quickly. Death often occurs soon after.
If malignant acanthosis nigricans is suspected in a patient without known cancer, it is extremely important to perform a thorough workup ( history, examination and relevant investigations as per history and examination ) for underlying malignancy and identify a hidden tumour. If the tumour can be successfully treated, the condition may resolve.
Other causes of acanthosis nigricans may be identified by screening for insulin resistance and diabetes mellitus.
Treatment for Acanthosis Nigricans
The primary aim of treatment is to correct the underlying disease process.
Often correcting the underlying cause results in resolution of the lesions.
  • Correct hyperinsulinaemia through diet and medication
  • Lose weight with obesity-associated acanthosis nigricans
  • Excise or treat the underlying tumour
  • Stop offending medicines in drug-induced acanthosis nigricans
In hereditary acanthosis nigricans, lesions tend to enlarge gradually before stabilising and/or regressing on their own.
There is no specific treatment for acanthosis nigricans.
Treatments considered are used primarily to improve cosmetic appearance and include topical retinoids, dermabrasion and laser therapy.
Final outcome of acanthosis nigricans varies depending on the cause of acanthosis nigricans.
Benign conditions either on their own or through lifestyle changes and/or treatment have good outcomes. However, the prognosis for patients with malignant acanthosis nigricans is often poor. The associated cancer is often advanced and the average survival of these patients is approximately 2 years.
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