Neurofibromatosis is one of the phakomatoses (“birthmarks”), the congenital or heritable conditions characterized by hamartomas and neoplasms throughout the body. The phakomatoses include Neurofibromatosis, Tuberous sclerosis, von Hippel-Lindau disease (retinal capillary hemangioma), Sturge-Weber syndrome, ataxia-telangiectasia and Wyburn-Mason syndrome.
Neurofibromatosis types 1 and 2 share some clinical features; and both are inherited in an autosomal dominant pattern. Type 2 (NF2) is characterized 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 remodeling and tumor suppression. Patients develop acoustic neuromas (vestibular schwannomas), which are often bilateral. Other central nervous system tumors are less common, and include neurofibromas, meningiomas and gliomas. The principal ocular complication is juvenile posterior subcapsular cataract, which affects two-thirds of patients and usually develops before age 30. Hamartomas of the retinal pigment epithelium and retina are common.
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 subcapsular cataracts may cause blurred vision or glare. As with NF1, café-au-lait patches are asymptomatic; and neurofibromas may cause cosmetic disfigurement or discomfort.
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 percent, while Lisch nodules are rare. (for details, see Neurofibromatosis Type 1).
Posterior subcapsular 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 percent of patients.
Very rare (1 per million). Optic nerve gliomas are rare (1/100,000).
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.
Neurofibromatis Type 1, Cataract, Tumors of the Retinal Pigment Epithelium
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.
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.
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.
Thorough neurological examination at regular intervals is appropriate.
Retinal astrocytic hamartoma in the right superior fundus of a 10 year old boy, appearing as a “fish egg” like-lesion. Tests for tuberous sclerosis and neurofibromatosis proved negative and this was presumed to be an isolated finding. Image courtesy of Clinical and Experimental Optometry journal.
Optic nerve glioma with hemorrhage, associated with neurofibromatosis.