“Funny-looking” Moles : Dysplastic Nevi.

Many patients present to a plastic surgeon’s office concerned about a “funny-looking mole”. The medical term for this a dysplastic nevus (pl. nevi). The most important diagnostic exclusion is that of melanoma.

What is a dysplastic nevus ?

A dysplastic nevus is defined as a pigmented area, which is caused by a proliferation of melanocytes, the cells which produce pigment (see picture below), which show histological features of concern and which may be associated with an increased risk of melanoma. Not all pigmented areas have these abnormal proliferation patterns and thus not all pigmented areas can be called nevi.


What does it look like ?

Dysplastic nevi are variably pigmented, ranging from light brown to very dark and may also show other colours such as blue or white (which are very suspicious colours). They may have a raised area and usually are more than 5mm in greatest diameter and have irregular, fuzzy edges. Variable asymmetry is also very common. Examination by a pathologist under a microscope is the only definitive way to diagnose a dysplastic nevus. On examination it is usually a constellation of features rather than any single feature that raises the clinical suspicion. I like to use the C.A.S.H. system as it gives numerical score to each mole. Those with a score of less than 7 are usually benign.

Where do they occur ?

Dysplastic nevi occur in up to 10% of the population. Patients may be born with them, but they usually increase in number during puberty. New nevi may also occur in adult life. They can occur anywhere on the body (even on the breasts or buttocks which are usually covered with 2 layers of clothing), although they usually occur on the intermittently sun-exposed areas such as the back. They may be “dysplastic” at their first appearance or they may develop more atypical features with time, especially in “moles” with a so-called “junctional component”.

What is the risk attached to a dysplastic nevus ?

Dysplastic nevi are associated with an increased risk of melanoma – 15 times higher than patients without them. If a patient has dysplastic nevi AND has had a melanoma before, the risk of another melanoma is 100 times higher than the normal. If a patient with a dysplastic nevus has had a melanoma before, and has a first degree relative with a melanoma, their risk of another melanoma rises to 1500 times more than the normal.

Melanoma arises within a dysplastic nevus in about 50% of cases (44-80% in different studies). This means that the other 50% of melanomas come from otherwise normal looking skin. Each dysplastic nevus however, has only a 1 in 10 000 lifetime risk of becoming a melanoma – a very low risk.

What to do about them?

Having dysplastic nevi is a melanoma risk, but each nevus is actually low risk, as described above. This means that simply cutting them out will only reduce the risk for that patient very marginally. Most international guidelines do not support such prophylactic excisions.

Self-examination is cheap and non-invasive and is often recommended despite the lack of scientific evidence.

Genetic screening for CDKN2A mutations is a promising avenue to screen at risk patients, but correlation with melanoma risk is not perfect and it is expensive and is thus not recommended except in the context of clinical trials.

Ocular examination (examination of the retina, done by an ophthalmologist) has been associated with an earlier detection of melanoma of the retina and annual screening in very high risk patients is recommended.

The most important screening tool is digital epiluminescent microscopy (mole-max or mole mapping) done by a dermatologist. It gives a much clearer view than can be achieved with the naked eye and stores the digital image for future reference. “Moles” that are suspicious are then referred to the plastic surgeon for excision. This method improves the diagnostic yield and limits unnecessary surgery, while providing the optimal risk management for these patients.

Sunscreen use has been associated with lower numbers dysplastic nevi and should form part of the risk management strategy for patients.

My Personal Recommendation :

  1. All patients should perform monthly self-examination of their “moles”.
  2. All patients should wear sunblock with SPF 30 or greater every day. Additional clothing cover should be used whenever possible.
  3. At risk patients should be screened with a mole-max scan annually. Any suspicious moles should then be excised.
  4. An ocular examination should be done every 2 years, except in higher risk patients, when it should be done annually.
  5. If a patient is bothered in any way by their “moles” I remove them.