Medical Challenges Associated with Large CMN


One of the primary medical challenges presented to people with large nevi is lack of accurate information provided by many professionals. Because it is a relatively rare condition, most doctors have never had experience with large congenital melanocytic nevi (LCMN). Misinformation is often more common than not, and many new parents are given an incorrect and often frightening prognosis, or simply not given information at all.

More Than Skin Deep

Because it is primarily a skin disease, it is common for people, some doctors and insurance companies included, to think of LCMN as only an appearance challenge. However, there can be more to it than that. Here are some other things that can happen with LCMN.

Malignant Melanoma

The risk of a person with LCMN developing malignant melanoma is not over 5%, and most likely less than 2%.

The bad news is: some number of people born with a large nevus develop melanoma, a serious form of cancer. The good news is: scientists don’t understand the mechanisms involved well enough to say for sure that a particular person with a large nevus got melanoma because they have a large nevus. They also can’t say for sure that this person would not have developed melanoma if they did not have a large nevus.

For decades logic has gone like this:

  • A nevus is mole
  • Moles are known to be a risk for cancer
  • Large nevi are really big moles
  • Therefore, people with large nevi must be at greater risk for melanoma

Science today is not saying this is not true, but science today is having a hard time agreeing with science of yesterday who routinely thought of having a large nevus as almost automatically meaning you would get cancer. Whereas you can find (older) medical articles saying the risk of malignant transformation (i.e. getting cancer) for a person with a nevus is 20-40%, we have better numbers today than the authors who wrote those articles, and the number is not over 5% and most likely less than 2%.

Neurocutaneous Melanocytosis (NCM)

(This used to be called neurocutaneous melanosis, but we’re talking about the same thing). People with large nevi, and also people who don’t have a large nevus but who were born with numerous smaller congenital nevi, can have melanocytes (nevus cells) in their central nervous systems (their brains and/or spinal cords). These cells produce melanin. Melanin does not particularly belong in your brain, and it can cause complications when present.

It is estimated that 93% of people who have a large nevus or multiple congenital nevi do not have NCM. More than half (60%) of the remaining 7% who do have NCM, don’t have complications from it, even though the melanin is present in their brain or spinal cord. The few who do have complications usually have a relatively good long term prognosis. Many of those with complications have seizures caused by NCM but no other symptoms. If the seizures can be controlled, the patient can lead a relatvely normal life.

Occasionally, a person with NCM may have complications so severe that their prognosis is not so good. About 1% of people with a giant nevus cannot survive these complications. These other symptoms include hydrocephalus, unconsciousness, vomiting, and certain reflex and eyesight issues.

How do I know if I have NCM?

If you have a large nevus or multiple congenital nevi, and you have any of these neurological symptoms listed, ask your doctor to screen you for NCM. NCM can be detected on an MRI if it is done correctly. Here is a paper about MRI scans for NCM.

What can be done about NCM?

There is no treatment for NCM itself. There are various things that can be done for various symptoms. In some cases, removing melanin deposits from the brain appears to be able to stop seizures permanently, but this depends on where the melanin is located. Some parts of the brain are inoperable. A person with symptomatic NCM should be under the care of a neurologist.

Looking for a doctor?

Nevus Outreach, Inc. does not endorse any doctors or medical professionals. We know many new nevus parents, though, are looking for a doctor who has experience working with large nevi. We have compiled a list of doctors who are used by our members. We make no claims or recommendations of these doctors.

Nevus Doctors Join a Support Group Teenage girl with CMN

Two girls with nevi at the Nevus Conference

Psychological Challenges

In addition to these medical issues, nevus owners can face many psychological challenges from the reactions of strangers, friends, & family or the nevus owner's self-perception. While experiencing these social and psychological challenges can be difficult, the Nevus Outreach community is here to offer support and encouragement to help you face them in a healthy and constructive way. Visit our Psychological Challenges page to learn more »