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Neurofibromatosis types 1 and 2 share some clinical features and both are inherited in an autosomal dominant pattern. Type 2 (NF2) is characterised by bilateral acoustic neuromas and a high risk of cataract. The affected gene is on chromosome 22, and encodes a protein called Merlin, which has been implicated in cell surface remodelling and tumour suppression. Patients develop acoustic neuromas (vestibular schwannomas), which are often bilateral. Other central nervous system tumours are less common, and include neurofibromas, meningiomas and gliomas. The principal ocular complication is juvenile posterior sub capsular cataract, which affects two-thirds of patients and usually develops before age 30. Hamartomas of the retinal pigment epithelium and retina are common.
Symptoms
Acoustic neuromas typically present in the second or third decade with hearing loss, tinnitus and/or loss of balance. Symptoms of fifth, sixth or seventh cranial nerve dysfunction may ensue. Juvenile posterior sub-capsular cataracts may cause blurred vision or glare. As with NF1, café au lait patches are asymptomatic and neurofibromas may cause cosmetic disfigurement or discomfort.
Signs
Café au lait spots occur in approximately two-thirds of patients. They are less numerous than in NF1, and tend to be restricted to the trunk. Cutaneous neurofibromas occur in approximately 30 per cent, while Lisch nodules are rare. (See Neurofibromatosis Type 1, Optician, September 21, 2007). Thickened corneal nerves, with a coarse silvery appearance, are more common in NF2 than NF1
Posterior sub-capsular cataracts have a characteristic granular appearance immediately anterior to the posterior lens capsule. Neurological examination, with particular attention to the cranial nerves, may reveal signs such as hearing or balance impairment, as in acoustic neuroma. Extraocular motility defects occur in 10 per cent of patients.
Incidence
Very rare (1 per million). Optic nerve gliomas are rare (1/100,000).
Significance
Cataract may cause significant loss of vision. Central nervous system neoplasms have the potential to substantially impair neurological function, and may require major surgery with its attendant risks.
See also
Neurofibromatosis Type 1, Cataract, Tumours of the retinal pigment epithelium.
Management
Genetics
After the collection of a detailed family history and examination of all family members, the patient should be advised that, on average, half of their children will be affected by this autosomal dominant condition.
Additional investigations
Suspected central nervous system tumours are investigated with computed tomography (CT) or magnetic resonance imaging (MRI). Electroencephalogram (EEG) and audiography are employed in the preoperative assessment of acoustic neuroma.
Surgery
Several methods, involving surgery and radiotherapy, are employed in the removal of acoustic neuromas. They are best removed at an early stage for optimal preservation of hearing and facial nerve function.
Review
Thorough neurological examination at regular intervals is appropriate.