Neurofibromatosis

• Neurofibromatosis is a genetic condition that causes nerve tumours (neuromas) to develop throughout the nervous system.
• These tumours are benign but can cause neurological and structural problems.
• Neurofibromatosis type 1 is more common than neurofibromatosis type 2.
• The neurofibromatosis type 1 gene is found on chromosome 17.
• The neurofibromatosis type 1 gene codes for a protein called neurofibromin, which is a tumour suppressor protein.
• Mutations in the neurofibromatosis type 1 gene are inherited in an autosomal dominant pattern.
• Diagnosis of neurofibromatosis type 1 is based on the diagnostic criteria and genetic testing can be helpful.
• Neurofibromatosis type 2 is associated with mutations in the neurofibromatosis type 2 gene on chromosome 22, which codes for a protein called merlin, a tumour suppressor protein important in Schwann cells.
• Mutations in the neurofibromatosis type 2 gene lead to schwannomas, benign tumours of the Schwann cells, and inheritance is autosomal dominant.
• A single plexiform neurofibroma is significant.
• Schwann cells provide the myelin sheath that surrounds neurones of the peripheral nervous system.
• A single skin neurofibroma without other features does not indicate neurofibromatosis.
• Neurofibromas may be seen on the skin and are skin-coloured, raised nodules or papules with a smooth, regular surface.
• Complications of neurofibromatosis type 1 can include migraines, epilepsy, renal artery stenosis, learning disability, behavioural problems, scoliosis of the spine, vision loss, malignant peripheral nerve sheath tumours, gastrointestinal stromal tumour, brain tumours, spinal cord tumours, and an increased risk of cancer.
• There is no treatment for the underlying disease process of neurofibromatosis type 1, management involves monitoring, managing symptoms and treating complications.
• Surgery can be used to resect acoustic neuromas, although there is a risk of permanent nerve damage.
• An exam patient with bilateral acoustic neuromas almost certainly has neurofibromatosis type 2.
• A plexiform neurofibroma is a larger, irregular, complex neurofibroma containing multiple cell types.
• Two or more skin neurofibromas are significant.
• The diagnostic criteria for neurofibromatosis type 1 are based on the features, remembered with the “CRABBING” mnemonic: C for café-au-lait spots, R for relative with NF1, A for axillary or inguinal freckling, BB for bony dysplasia, such as bowing of a long bone or sphenoid wing dysplasia, I for iris hamartomas (Lisch nodules), which are yellow-brown spots on the iris, N for neurofibromas, G for glioma of the optic pathway.
• Neurofibromatosis type 2 is particularly associated with acoustic neuromas, tumours of the auditory nerve that innervates the inner ear.