Melanosis neurocutanea Q03.8

Rare (congenital) non-hereditary, neuroectodermal dysplasia with multiple, disseminated, mostly extensive melanocytic nevi of the skin and leptomeninx, possibly also of the brain and spinal cord. Further cerebral hamartomas may be associated. It is not uncommon for an internal hydrocephalus to develop.

Prevalence: Approx. 1/20,000 newborns. Neurocutaneous melanosis affects a small proportion of patients with the common congenital melanocytic nevi (CMN) and is characterized by large (giant) CMN in combination with an often symptomatic leptomeningeal melanosis.

Neurocutaneous melanosis affects a small proportion of patients with the common congenital melanocytic nevi (CMN) and is characterized by large (giant) CMN in combination with an often symptomatic leptomeningeal melanocytosis. It is caused by an early embryonic NRAS mutation in the neuroectoderm. The risk of melanoma depends on the extent of the CMN and is around 1% for CMN in general compared to 12% for giant CMN. In neurocutaneous melanosis, there is also an increased risk of CNS melanoma.

Melanocytic nevi exist from birth. Neurological symptoms usually manifest by the age of 2.

Large congenital melanocytic nevus (> 20 cm in adults, 6-9 cm in infants). The large congenital melanocytic nevi (LCMN) are localized on the trunk in > 50% of patients and on the head and upper arm/thigh in 15% each.

Mostly dense seeding of small-spotted, occasionally also large-area, differently intensely pigmented, congenital melanocytic tumor formations, which can also affect the palms of the hands and soles of the feet. The risk of developing, often aggressively growing melanomas already exists in childhood.

Some patients with neurocutaneous melanosis remain asymptomatic.

Symptomatic forms with the development of neurological symptoms (hydrocephalus with symptoms of intracranial pressure, convulsions, impaired consciousness, spinal cord compression) occur in 7- 10% of cases with LCMN. Furthermore, hemiplegic malformations of the brain with polymicrogyria, pachygyria and sublobar dysplasia have been reported (Kumar I et al. 2019).

Apparently, leptomeningeal involvement occurs more frequently in patients with LCMN and satellitosis. Melanocytic nevi can proliferate at the leptomeninges and lead to hydrocephalus internus with corresponding neurological symptoms.

Danger of developing a leptomeningeal melanoma! Proliferating neurogenic hamartomas and cerebellar astrocytomas have also been described (Garrido MC et al. 2019; Wang X et al. 2018)

Dermatology: The skin manifestations primarily serve as a leading symptom. Otherwise excision of conspicuous nevus areas, therapy attempts by means of early dermabrasion are successful, but are not an option due to the multiplicity of the large-area nevi

Neurological: In the presence of extensive or multiple pigmented nevi, clarification of neurological involvement using MRI is recommended.

In the case of acute symptoms (in early childhood, e.g. frequent hydrocephalus internus) neurosurgical intervention.

Prevention: Important (but unfortunately without consequences) is the lifelong monitoring and targeted clarification of any accompanying neurological symptoms using MRI or CT.

Unfavorable; A part of the affected patients dies within the first 3 years after the onset of symptoms. The neurological involvement often leads to internal hydrocephalus with cerebral pressure symptoms.

Remember! Patients with large congenital melanocytic nevi (10-20 cm) and giant melanocytic nevi (> 20 cm) have a significantly higher risk of neurocutaneous melanosis. The risk is even higher if multiple satellite nevi are present in the vicinity of a giant melanocytic nevus, the melanocytic nevi are disseminated throughout the whole integument and are located in the so-called "posterior axis localization" (head, neck, back, buttocks).

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