Frequently Asked Questions about CMN


Questions about CMN? We're here to help.

Here are the answers to the questions we get asked the most about large congenital melanocytic nevi (also referred to as CMN). Our goal is to provide you with the information you need about large/giant congenital melanocytic nevi. If you have further questions after reviewing these questions, feel free to contact us.

What is a congenital melanocytic nevus?

In a nutshell, a nevus is a birthmark. But, there is much more to learn than that. There are several types of nevi: epidermal, melanocytic and connective tissue nevi. Nevus Outreach deals with large and giant congenital melanocytic nevi. Large, in nevus terms, is generally bigger than the palm of your hand. Congenital means it is present at birth. Melanocytic means that it is pigment-based. Want to know more? You probably do... that's why you're here! Visit the "What is a Large/Giant Congenital Melanocytic Nevus" page for more information.

Small, Large, Giant... How are nevi measured?

Since nevi can be found on any part of the body, and grow as the body grows, the term large can be difficult to define. Doctors don’t all use the same definitions.  The most common indicators that a nevus can be described as a large nevus can be found on the "What is a Large/Giant Congenital Melanocytic Nevus" page. You can also see the generally accepted classifications of nevi here.

How common are congenital nevi?

Small melanocytic nevi are very common. One in every 50 to 100 people is born with a small melanocytic nevus. Large congenital nevi are more rare and occur approximately once in every 20,000 births. Giant congenital nevi are thought to occur approximately once in every 500,000 births.

How is nevus-skin different?

Nevi are much more than simply dark skin. Besides producing increased pigmentation, the area covered by a melanocytic nevus often produces increased amounts of hair. It can often look like a very large mole or a large birthmark. The formation of sweat glands can be disrupted in nevi – so sometimes a person with a large nevus may not sweat where their nevus is located. Many nevi lack subcutaneous fat, a layer of fat just under the skin that pads the body everywhere. Some nevi will also have neurofibromas or other neural tumors, within their borders. These growths are not painful and are normally superficial. Nevus-skin can range from thick with a folded appearance, to thin and fragile. Fragile skin can tend to tear more easily and may take a longer time healing.

Is it Painful?

Although a large nevus doesn't generally cause pain, some aspects of the affected skin can be uncomfortable. Nevus skin can itch. Also, since there is often a lack of fatty tissue under a nevus, it isn't as well padded as other parts of the body so it may be more affected by continuous pressure. Nevus skin can also be more fragile than other skin, making it prone to tearing... and just like it sounds, yes, tearing hurts.

What causes nevi?

Large congenital melanocytic nevi form in the womb very early in development, within the first twelve weeks of pregnancy. They are caused by a mutation during embryologic development. There is no known method of prevention. They appear in both sexes, in all races, and on any areas of the skin.

What doesn’t cause nevi?

At Nevus Outreach, we frequently hear from parents wondering what they must have done to cause their baby to be born with a large nevus. It is important to realize that nothing you did caused your child to be born with a nevus. Large or Giant Congenital Melanocytic Nevus are not hereditary, meaning you did not "pass it on" to your child. Additionally, we know of no cases where alcohol, drugs, diet, illness, injury or any other external factor for a parent can be linked to the formation of a large nevus in their child.

Nothing you did caused your child to be born with a nevus. It is not your fault.

Can nevi pose a health problem?

In terms of physical health, pigmented moles have been linked to melanoma, a potentially deadly skin cancer. Also, certain children with large nevi may have melanin, melanocytes and/or nevomelanocytes in their central nervous systems (the brain and spinal cord). This condition is known as neurocutaneous melanocytosis (melanosis) (NCM). Most people with NCM do not have neurological problems. However, some do, and the complications from NCM can be very serious. Visit the "Medical Challenges" page to learn more.

Having a large nevus can impact one’s mental health and well-being. Large nevi are obvious and unusual. These can be difficult hurdles to overcome. Visit the "Psychological Challenges" page to learn more.

Which moles may develop melanoma?

Scientific opinions vary as to the exact risk of melanoma, but current research indicates that the number of children born with large nevi who develop melanoma later in life to be between 2-5%. Any congenital nevus, small or large, may develop melanoma, but those of greatest concern are very large or thick. 

What are the signs of melanoma?

Changes in size, color, surface texture, pain, bleeding, or itching are all of concern. Any such changes should be evaluated medically if they last longer than two weeks. Additionally, the presence of a lump which you can feel under a large congenital nevus may be of concern, since melanoma may arise deeper in a larger nevus. If melanoma is suspected, usually a small sample of the mole is removed and sent to a pathologist for diagnosis.

What should be done about a congenital nevus?

It's the question everyone asks, but there is no simple answer. Because of the rarity of this condition, as well as the lack of understanding of large nevi among doctors, there is a wide range of professional opinion regarding how to treat large congenital nevi. However, there is a reasonable consensus on the first few diagnostic steps. Nevus Outreach has worked with worldwide experts in the field to develop a set of Best Practices Guidelines, which can help you and your doctor determine how to proceed. Work closely with your doctor, who may refer you to a dermatologist specializing in pigmented skin lesions. Where NCM is suspected, you may be referred to a neurologist. These evaluations may lead to other tests such as a skin biopsy and/or an MRI.

Is removal of the nevus an option?

In some cases, a large nevus can be removed and replaced with skin from the nevus patient. Removal of a large nevus is a major surgery and there are many aspects to consider. We have prepared some basic information about nevus removal here.

Why remove a nevus?

Most of the time, the overriding reasons to remove a pigmented nevus are first to reduce melanoma risk and second to improve appearance which can be fundamental to improving a patient’s overall psychosocial state. Other reasons to remove a nevus may be to improve the strength, texture, sensation, and sweat gland activity of the affected area.

Some people choose to leave their nevi intact, while others choose to remove them. There are good reasons for both choices. It is a highly personal decision.

How often should individuals with congenital nevi be examined?

Like all moles, large nevi should be examined regularly by a physician. A mole’s color may stay the same, lighten slowly, or darken slowly over time. Hair in a mole is not an indication of whether it is malignent or benign. On the other hand, any rapid or persistent change in color, texture, or outline, or the development of a new nodule, is cause for immediate examination by your doctor. If scars are present they should be examined visually for pigment recurrence and should also be palpated so as to help detect growths that may develop under the top layer of the skin.

Where can I find a doctor who has experience with LCMN?

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. The best place to get the information you seek is by becoming a Member of Nevus Outreach. You can ask questions about experts in your area and what other people have experienced. 

Nevus Removal CMN Glossary Medical Challenges Psychological Challenges Treatment Options Nevus Doctors Teenager with a nevus graduating from high school

Boy with nevi playing at the pool

Teenage girl with nevi

Still have Questions?

Don't worry; finding out that your new child has CMN can be overwhelming, but we're here to help. Visit our What is a CMN page for a more in-depth definition of the condition, or feel free to contact us. We'd be happy to get to know you and answer any questions you may have.

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