Neurofibromatosis

Contributed by Dr Jean Watkins, a retired GP in Hampshire

Melanocytic nevi

Melanocytic nevi are due to benign proliferations of melanin-producing melanocytes that colour the area brown. They may be present at birth, develop in early childhood or adolescence. Many fade and disappear with age. Apart from a patient's concern about appearance, these naevi are not of any significance. This 24-year-old girl, however, requested removal of this mole because she did not like it. Otherwise, the only concern is the rare chance of malignant change. In these cases, one would expect the mole to change in size or colour, get larger or bleed or crust.

Axillary freckling


Another important feature of neurofibromatosis is axillary freckling in which small pigmented macules occur in the axilla and the perineum (Crowe's sign). Type-1 neurofibromatosis is linked to the gene NF-1, localised on chromosome 17. Diagnosis of this condition is suggested if there are more than two of the following features present: six or more cafe au lait spots larger than 5mm in diameter in prepubertal youngsters, two or more neurofibromas, axillary or inguinal freckling, optic glioma or a first degree relative with type-1 neurofibromatosis.

Complications of neurofibromatosis


Cutaneous lesions may be unsightly, or as in this case interfere with footwear. However, problems with these are less serious than in those with internal manifestations of the disease. Malformation of the long bones or scoliosis, growth hormone deficiency and short stature, learning difficulties with mental retardation in 5-10 per cent, optic nerve tumours that affect vision, hypertension, and epilepsy related to cerebral tumours or obstruction or bleeding due to tumours in the GI tract are all associated problems.

Deafness

Deafness may occur if there is involvement of the acoustic nerve. As well as multiple tumours on the brain and spinal cord, tumours on the auditory nerves may present the first sign of the condition. This may not occur until the early twenties. Dizziness and tinnitus may be a feature. Bilateral vestibular tumours can be associated with type-2 neurofibromatosis. Audiogram, CT and MRI scans will be necessary to site and size the tumour. Early diagnosis is important as larger tumours may also involve the facial nerve and balance and are more difficult to excise surgically.

Cafe au lait spots

Cafe au lait spots are seen in neurofibromatosis. They may be present at birth but more commonly develop in the first three years of life. They are seen as irregularly shaped, pigmented brown macules. As such lesions are common in normal people, it is suggested that six or more such lesions of more than 1.5cm in diameter would be necessary to suggest the diagnosis. A family history of this autosomal dominant condition would greatly increase the likelihood of neurofibromatosis.

Cutaneous nodules


Superficial, cutaneous tumours may be seen in neurofibromatosis. They may be few in number, or as in this case, numerous. There had been tell-tale cafe au lait spots since infancy and then the 'button like' tumours began to appear when she was 12. There was a family history of the condition and her daughter was also affected. The risk of passing the gene on to children is 50 per cent. These tumours are benign but enlargement of them may compromise vital structures. Surgery may be possible in some of these cases. There is a small risk (3-15 per cent) of malignant change.

Segmental neurofibromatosis (Neurofibromatosis Type 5)

Segmental neurofibromatosis is a rare variant of the condition in which cutaneous neurofibromas are limited to one area of the body. Cafe au lait spots may, or may not be present. The lesions are usually unilateral and most likely to affect the cervical or thoracic dermatome. This patient had developed a large 'mole' on her left shoulder as a child. As she grew, it had gradually increased in size. On examination the lesion was raised and had a 'flabby texture'. Biopsy of the lesion confirmed the diagnosis of segmental neurofibromatosis.

Neurofibromatosis Noonan syndrome

It has been found that some patients with neurofibromatosis manifest signs that could be confused with a patient such as this, with Turner's syndrome. Particular features of Noonan syndrome in a patient with neurofibromatosis are short stature, webbed neck (such as is seen in this patient), learning problems and muscle weakness. It has been suggested that neurofibromatosis Noonan syndrome is a rare variant of type-1 neurofibromatosis caused by mutations on the NF-1 gene.

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