What is congenital melanocytic nevus?
The congenital melanocytic nevus (CMN) is a dark, pigmented, often hairy patch of skin. A congenital melanocytic nevus is present at birth or appears soon after birth.
The congenital melanocytic nevus lesions, are classified according their sizes. There are several classification systems proposed, but the system proposed by Kopf et al. is the most accepted. The CMN lesion present at birth that will reach a diameter of 20 cm or more in adulthood is classified as giant congenital melanocytic nevus (aka bathing trunk nevus, garment nevus or giant hairy nevus). The CMN lesions having a diameter less than 2 cm are considered as small-sized and those having a diameter more than 2 cm but less than 20 cm are considered as medium-sized.
Giant congenital melanocytic nevus (GCMN)The giant congenital melanocytic nevus is a rare entity and its incidence is about one in every 20,000 births.
Some peculiar locations and shapes of the hairy nevi lead to use of descriptive terms like 'garment', 'bathing trunk', 'shirt', 'coat sleeve' or Hairy giant nevus. Satellite lesions, small pigmented lesions scattered over the body, are observed in nearly 80% of the giant CMN patients. Satellite lesions associated with giant hairy CMN may be present in odd places like oral cavity, scalp, eyelids and planter areas. The giant hairy CMN may disturb the skin structure, causing cutaneous fragility, impaired sebaceous and eccrine glands and superficial ulcers.
Psychosocial issuesThe unsightly appearance of the hairy nevi is psychosocially devastating for the affected person and his family members. The psychological consequences of the hairy nuvi in visible areas like face are many. Nearly 25% of the patients suffer from emotional or behavioral problems. Nearly 30% of patients have to face social problems. The impaired self-image caused by the presence of the giant hairy CMN, the anxiety over the risk of complications and the unsightly appearance contribute in compounding the psychological symptoms in the patients and other family members.
PathogenesisThe giant congenital melanocytic nevus lesion originates during 5th and 24th week of gestation.
|Giant hairy congenital melanocytic nevus in a young girl with neurocutaneous melanosis|
The size of the hairy nevus depend upon how early the accelerated proliferation of cells of melanocyte lineage has started. The melanocyte proliferation commencing after birth produces acquired melanocytic nevus. A small CMN will result if the proliferation of melanocytes in the dermal-epidermal junction begins shortly before birth. Giant and medium-sized nevi would develop when the proliferation starts, during migration of melanoblasts from the neural crest to epidermis. The giant congenital hairy nevus will be large and deep seated if the proliferation starts during the embryonic or early fetal periods.
Progression over timeThe progression over time of the hairy lesions is unpredictable. Some GCMN may get lightened over time whereas some may darken. As the hairy lesion progresses the pigmentation may get more heterogeneous or homogeneous. The hairy growth may increase over time. In some patients the hairy growth may disappear. In very rare cases the giant congenital hairy lesions may spontaneously regress. In some cases it was reported that the lesions darkened through adolescence and then significantly lightened. The surface undergoes changes such as increase in roughness, thickness, hairy growth and appearance of nodules.
Health risks from giant congenital melanocytic nevusThe giant congenital melanocytic nevus in some cases develop into malignant melanoma or neurocutaneous melanosis with melanocytic tumors in the leptomeninges. The estimated lifetime risk of developing melanoma varies from 5 to 10%. There is the possibility for simultaneous occurrence of disorders like diffuse lipomatosis, atrophy and asymmetry of limbs, scoliosis, urinary tract anomalies, cafe-au-lait spots and Mongolian spots.
Melanoma associated with hairy giant congenital melanocytic nevusThe melanoma affecting patients with GCMN occurs usually in the dermis or in deeper layers. Most of other melanomas arise in the epidermis. In a study of 289 patients with hairy giant congenital melanocytic nevus, Dedavid et al. found 67 cases of melanoma. 50.7% of these melanoma appeared on the lesions. 3% of the melanomas appeared on clinically normal skin. 31.3% of them were primary central nervous system (CNS) tumors and 15% were metastatic tumors spread from unknown primary site.
Patients having multiple satellite nevi and hairy giant congenital melanocytic nevus on locations such as the back, neck or head have the increased risk of developing melanoma. The probability of a GCMN patient developing melanoma is more in the early childhood. Dedavid et al. found that 50% of the melanomas were diagnosed before five year age. Benign tumors may also develop on the hairy melanocytic nevus.
Neurocutaneous melanosis (NCM)Neurocutaneous melanosis is a congenital disorder associated with the presence of giant congenital nevus on the skin and melanocytic tumors in the leptomeninges. These lesions occur in brain and spinal cord. Nearly 50% of the patients with NCM develop malignancy. It occurs in the form of leptomeningeal melanoma. The cause is believed to be related to abnormal development of melanoblasts and mutations of the NRAS gene. Some of the symptoms of NCM are, increase in intracranial pressure, seizures, vomiting, headache and papilledema. There is no effective treatment for the disorder.
TreatmentSeveral treatment options are available for treating hairy congenital melanocytic nevus. The age of the patient, size and location of the lesion and risk of melanoma are to be considered while selecting a treatment option. Surgery, dermabrasion, skin curettage, chemical peels and laser treatment are the options available.
1.Arpaia N, Cassano N, Filotico R, Laricchia F, Vena GA. Unusual clinical presentation of regression in a congenital melanocytic nevus. Dermatol Surg 2005;31:471-3.
2.Martín JM, Jordá E, Calduch L, Alonso V, Revert A. Progressive depigmentation of a palmar congenital melanocytic nevus without an associated halo phenomenon. Dermatology 2006;212:198-9.
3. Nath AK, Thappa DM, Rajesh NG. Spontaneous regression of a congenital melanocytic nevus. Indian J Dermatol Venereol Leprol 2011;77:507-10.
4.Gass JK, Grant JW, Hall PN, Atherton DJ, Burrows NP. Clinical resolution of a neonatally eroded giant congenital melanocytic nevus. Pediatr Dermatol 2006;23:567-70.
5.Ana Carolina Leite Viana, Bernardo Gontijo, Flávia Vasques Bittencourt. Giant congenital melanocytic nevus. An Bras Dermatol. 2013 Nov-Dec; 88(6): 863–878.