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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