Neurofibromatosis

Neurofibromatosis is a genetic condition that causes nerve tumours (neuromas) to develop throughout the nervous system. These tumours are benign, however they do cause neurological and structural problems. There are two types of neurofibromatosis with different features. Neurofibromatosis type 1 is more common than type 2. The majority of this section focuses on type 1.

 

NF1 Gene

The neurofibromatosis type 1 gene is found on chromosome 17. It codes for a protein called neurofibromin, which is a tumour suppressor protein. Inheritance of mutations in this gene is autosomal dominant.

 

Criteria

There are clear diagnostic criteria for NF1 based on the classical features of the condition. There must be at least 2 of the 7 features to indicate a diagnosis. You can remember this with the mnemonic CRABBING.

  • CCafé-au-lait spots (6 or more) measuring ≥ 5mm in children or ≥ 15mm in adults
  • RRelative with NF1
  • AAxillary or inguinal freckles
  • BBBony dysplasia such as Bowing of a long bone or sphenoid wing dysplasia
  • IIris hamartomas (Lisch nodules) (2 or more) are yellow brown spots on the iris
  • NNeurofibromas (2 or more) or 1 plexiform neurofibroma
  • GGlioma of the optic nerve

 

Investigations

Diagnosis is based on clinical criteria and no investigations are required to make a definitive diagnosis.

Genetic testing can be used where there is doubt.

Xrays can be used to investigate bone pain and bone lesions.

Imaging with CT and MRI scans can be used to investigate lesions in the brain, spinal cord and elsewhere in the body.

 

Management

There is no treatment of the underlying disease process or to prevent the development of neurofibromas or complications.

Management is to control symptoms, monitor the disease and treat complications.

 

Complications

  • Migraines
  • Epilepsy
  • Renal artery stenosis causing hypertension
  • Learning and behavioural problems (e.g. ADHD)
  • Scoliosis of the spine
  • Vision loss (secondary to optic nerve gliomas)
  • Malignant peripheral nerve sheath tumours
  • Gastrointestinal stromal tumour (a type of sarcoma)
  • Brain tumours
  • Spinal cord tumours with associated neurology (e.g. paraplegia)
  • Increased risk of cancer (e.g. breast cancer)
  • Leukaemia

 

Neurofibromatosis Type 2

The neurofibromatosis type 2 gene is found on chromosome 22. It codes for a protein called merlin, which is a tumour suppressor protein particularly important in Schwann cells. Mutations in this gene lead to the development of schwannomas (benign nerve sheath tumours of the Schwann cells). Inheritance is autosomal dominant.

Neurofibromatosis type 2 is most associated with acoustic neuromas. These are tumours of the auditory nerve innervating the inner ear. Symptoms of an acoustic neuroma are:

  • Hearing loss
  • Tinnitus
  • Balance problems

Schwannomas can also develop in the brain and spinal cord with symptoms based on the location of the lesion.

Surgery can be used to resect tumours although there is a risk or permanent nerve damage.

TOM TIP: Bilateral acoustic neuromas almost certainly indicate neurofibromatosis type 2. This is a popular association in exams so worth remembering.

 

Last updated April 2019
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