Information on Congenital Melanocytic Nevi

Congenital Melanocytic Nevus: A medical term for a birthmark, or proliferations of pigment cells that are present at birth. (plural = nevi).

Satellite lesions (or moles): Smaller melanocytic nevi's away from the main nevus.

Classification of Congenital Melanocytic Nevi: Congenital Melanocytic Nevi (CMN) are usually classified by size.  There are several different classifications.  Modifications have been made to the way CMN's are classified, and the latest classification system was organized in 2013. That classification is as follows:

• Small: Less than 1.5cm (measured across the largest length of the nevus)

• Medium: two classifications - M1: 1.5 - 10cm, or M2: 10 - 20cm

• Large: two classifications - L1: 20 - 30cm, or L2: 30 - 40cm

• Giant: two classifications - G1: 40 - 60cm, or G2: greater than 60cm

• Satellite nevi: none, 1-20, 20-50, and greater than 50

McCoy's nevus has been classified by his pediatric dermatologist as a G1, with satellite nevi (or moles) being between 1 and 20. (He has approximately 11 small, very light satellites).

How common are congenital melanocytic nevi (CMN)?
     Small CMN occur in 1 in 100 births.
     Medium CMN occur in 1 in 1000 births.
     Giant CMN are much rarer, and only occur in 1 in 500,000 births.

They occur in all races and ethnic groups, and males and females are at equal risk.

CMN's vary in appearance: they can be single or multi-shaded, round or oval shaped pigmented patches.  They may have increased hair growth (hyertrichosis).  The surface may be slightly rough or bumpy.  CMN usually grows proportionally with the child.  Some may become lighter over time, other may become darker, raised, or more bumpy and hairy, particularly around the time of puberty.  CMN are usually asymptomatic, however some may be itchy, particularly larger ones.  It is thought there may be reduced function of sebaceous (oil) and eccrine (sweat) glands, which may result in skin dryness and a heightened sensation of itch.  The overlying skin may become fragile and erode or ulcerate.  Deep nests of melanocytes in the dermis weaken the bonds between the epidermis and the dermis and account for skin fragility.

Giant CMN (like McCoy's) are associated with an increased risk of developing cutaneous melanoma, neurocutaneous melanoma, and sometimes (but rarely) other tumors.  Neurocutaneous melanosis is a rare syndrome defined by the proliferation of melanocytes in the central nervous system (bain and spinal cord), and the presence of a congenital melanocytic nevus.  One is at a higher risk for neurocutaneous melanosis if: one has a G1 or G2 categorized nevus, and/or if one has a high number of satellite nevi.  It is estimated neurocutaneous melanosis affects 5-10% of people that have a giant CMN.  However, it is likely that the majority of cases remain asymptomatic, and the true incidence remains unknown.  The melanocytes in the brain and spinal cord may often be detected by an MRI scan. 

What causes congenital melanocytic nevi?

CMN are caused by localized genetic abnormalities resulting in the proliferation of melanocytes; these are cells in the skin responsible for normal skin color.  This abnormal proliferation is thought to occur between the 5th and 24th weeks of gestation.  If proliferation starts early in development, giant and medium sized CMN are formed.  Smaller CMN are formed later in development, after the melanoblasts (immature melanocytes) have migrated from the neural crest to the skin.

Risk of developing melanoma within congenital melanocytic nevi

The following characteristics of CMN are associated with the increased risk of development of melanoma (skin cancer):

• Large or giant size (like McCoy's)
• Axial of paravertebral location, meaning crossing the spine (like McCoy's)
• Multiple congenital satellite nevi (McCoy is considered to have few satellites)
• Neurocutaneous melanosis (McCoy's first MRI read has come back negative for this condition)
• Early childhood (it is said risk is highest for children with CMN to develop melanoma within the first 5 years of life)

The risk of melanoma is mainly related to the size of the CMN.  Small and medium sized CMN have a very small risk, under 1%.  Melanoma is more likely to develop in giant CMN.  Lifetime estimates are 5-10%.  McCoy's pediatric plastic surgeon, as well as his pediatric dermatologist, suggests that McCoy's risk is probably right around the 5% chance.  Melanoma can start deep inside the nevus or within any neuromelanosis found in the brain or spinal cord.  Very rarely, other tissues that contain melanocytes may also be a source of melanoma such as the gastrointestinal tract mucuosa.  In 24% of cases, the origin of hte melanoma cannot be identified. 50% of melanomas diagnosed in those with giant CMN occur at another site.

Melanoma associated with CMN can be very difficult to detect and treat.  The risk of development of melanoma is greater in early childhood; 70% of melanomas associated with giant CMN are diagnosed by the age of 10.  Rarely, other types of tumor may develop within giant CMN, including benign tumors and other malignant tumors (including sarcomas).

Reasons to consider surgical removal may include (according to doctors):

• Worry about risk of melanoma (removal reduces risk for giant CMN)
• Difficulty in observing the mole
• Recent change in the lesion (darkening, lumpiness, increasing size)
• Melanoma-like appearance (eg irregular shape, variegated color)