MOSAIC NEUROFIBROMATOSIS (or SEGMENTAL NEUROFIBROMATOSIS)

By Gary M. White, MD

mosaic neurofibromatosis. akak segmental neurofibromatosis Courtesy Michael O. Murphy, MD


In mosaic neurofibromatosis (MNF), also known as segmental neurofibromatosis, multiple neurofibromas and/or cafe-au-lait spots (CALS) occur in limited areas of the body due to mosaicism of the neurofibromatosis (NF1) gene. For investigative purposes, one can confirm the diagnosis of MNF buy verifying the blood as negative and the skin as positive for NF-1 mutations.

Clinical

The most common pattern is multiple, soft papules (neurofibromas) occurring grouped in one area of the skin. However, some patients may present with only CALS, with both CALS and neurofibromas, or with isolated plexiform neurofibromas. The involved area is usually just one segment, but may be more or even half of the body. Lesions are usually unilateral (approximately 6% of cases are bilateral) and occupy single dermatome In one review of 82 cases [J Am Acad Dermatol. 1997;37:864], the neurofibromas were mostly unilateral; however, bilateral neurofibromas were reported in five patients. The affected dermatomes were the cervical (31 patients), thoracic (33 patients), lumbar (20 patients), and sacral (5 patients) dermatomes.

In a review of 40 cases of MNF in children, 37.5% had 6 or more CALMs, but in all cases, the CALM were clearly distributed along a body segment [PD 2017;p34;271]. 62.5% had an underlying pigment delineating the segment.

Associations

Patients are at higher risk for hypertension, learning disabilities, seizures, Lisch nodules, scoliosis, skeletal abnormalities, malignancy and offspring with NF1 [Ped Derm 2016;33;9-17]. Some have reported an increased incidence of malignancy, particularly melanoma and peripheral nerve sheath tumors [Skinmed. 2010;8:156-9]. Further studies are needed to correctly define the risk here.

Risk of Offspring with NF-1

Individuals with MNF are at risk of gonadal mosaicism and thus having offspring with complete NF1 and its associated complications. The risk is somewhere in the 2.5-7% range [Ped Derm 2016;33;9-17] and seems to be higher in patients with pigmentary abnormalities.

Treatment

Patients should have a complete physical examination (including ophthalmologic examination), especially children with an emphasis on the potential associations as listed above. Patients should undergo routine health surveillance because of the risk of malignancy, especially if they have neurofibromas. With regard to individual lesions, excision of any bothersome, larger neurofibromas may be done.

Additional Photos

Two different patients with SNF on the back.
mosaic neurofibromatosis mosaic neurofibromatosis

mosaic neurofibromatosis mosaic neurofibromatosis

Four grouped NFs new onset on the arm of a 70 year old.
mosaic neurofibromatosis

References

Nodules and CALMs in same patient. Indian J Dermatol 2010;55: 105

Multiple papulonodules that were congenital. N Engl J Med. 2015 Mar 5;372(10):963

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