Neurofibromatosis

Neurofibromatosis is an autosomal dominant condition resulting in the growth of nerve tumours

Suggested approach to neurofibromatosis type 1 osce station

Describing lesions

• Neurofibromas
  • ‘There are multiple, well-demarcated brown circular nodules and papules present across the back in a generalized distribution.’          
  • ‘There are no secondary features (such as crusting, scaling or erosion).’
  • ‘On palpation, these lesions are soft and non-tender, with some exhibiting the button-hole sign.’
  • ‘These lesions are consistent with neurofibromas.’
• Café au lait spots
  • ‘There are also irregularly shaped, evenly pigmented, flat brown patches.’
  • ‘These are characteristic of café au lait spots.’
• Other areas
  • ‘I would like to look for axillary and inguinal freckling, and abdominal scars (e.g. for phaeochromocytoma surgery).’
• Conclusion
  • ‘Given there are 2 or more neurofibromas and 6 or more café au lait spots, the likely diagnosis is neurofibromatosis type 1.’
  • ‘In addition to examining the rest of the skin and taking a full history, I would like to measure blood pressure, do a full neurological exam for signs of spinal cord neurofibromas, examine the eyes for signs of optic nerve gliomas, and use a slit lamp to look for Lisch nodules on the iris.’

If you are allowed to ask the patient questions

• Family history
• Eyes, ears, blood pressure
• Any nerve lesions

Differential diagnosis

• Neurofibromatosis type 2
• Tuberous sclerosis (multi-system hamartoma formation)

Types of neurofibromatosis

Type 1 (peripheral) – most common

• NF-1 gene defect (chromosome 17) resulting in peripheral neurofibromas (i.e. in skin or subcutaneous tissue)
• Skin
  • Neurofibromas (2 or more): well-demarcated nodules which are erythematous and varied in size and shape 
  • Café au lait spots (6 or more): flat patch of asymmetrical darkened skin (brown/black)
  • Axillary freckling
• Other features
  • Optic nerve glioma → non-correctable visual loss
  • Lisch nodules (iris hamartomas, i.e. brown spots on iris seen with slit lamp)
  • Dorsal root spinal cord tumours
  • Plexiform neurofibromas (diffuse and invasive → bony erosion)

Type 2 (central)

• Merlin protein gene defect (chromosome 22) resulting in central schwannomas
• Most common presenting condition is bilateral acoustic neuromas (CN8) causing hearing loss, typically at 20-30 years of age
• Other conditions include: meningiomas, gliomas, juvenile cataracts
• Other symptoms include: headache, balance loss, vertigo, facial weakness, deafness, tinnitus
• Skin symptoms uncommon

Investigations

• Diagnosed on clinical features and MRI

Management

• Lifelong annual monitoring: vision, heart and blood pressure, hearing
• Treat complications
• Education