Neurocutaneous disorders and other syndromes

Aetiopathogenesis

The NF1 gene is a tumour suppressor gene, mapped to chromosome 1. Prenatal screening for the NF1 gene is available by amniocentesis or chorionic villus biopsy.

Clinical presentation

The two main cutaneous features are:

• 1.

  Café-au-lait spots : round or oval coffee-coloured macules, due to increased melanin pigment. They often appear in the first year of life. One or two café-au-lait spots are seen in 10% of normal people but, in neurofibromatosis, six or more are usually present. Freckling of the axilla is also found ( Fig. 51.1 ).

  

• 2.

  Dermal neurofibromas : small nodules that appear during childhood and increase in number at the time of puberty ( Fig. 51.2 ). Their number varies from a few to several hundred.

  

A proportion of patients with NF1 have short stature and macrocephaly. Rare variants of the disease are occasionally seen. The commonest is NF2 ( central neurofibromatosis ), in which patients have bilateral acoustic neuromas but few, if any, café-au-lait spots or dermal nodules. NF2 also shows autosomal dominant inheritance. The NF2 gene is on chromosome 22.

Complications

Many patients with NF1 have a benign course, but complications can include:

• ●

  Plexiform neurofibromas are larger than their dermal counterparts and measure up to several centimetres in size. They are associated with pigmentation and hypertrophy of the overlying skin or underlying bone, and present a cosmetic problem.

• ●

  Benign tumours of the nervous system may develop. These include optic gliomas, acoustic neuromas and spinal neurofibromas that arise from nerve roots of the spinal cord.

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  Sarcomatous change in a neurofibroma, typically non-cutaneous, occurs in 1.5%–15% of cases.

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  Kyphoscoliosis (in 2%) or bowing of the tibia and fibula may occur.

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  Other problems include iris hamartomas (Lisch nodules), hypertension, epilepsy and learning difficulties.