Type I Neurofibromatosis – NF1
- Autosomal dominant inheritance, although widely varying penetrance
- Gene on chromosome 17
Epidemiology and Aetiology
- 1 in 2500
- M:F – 1:1
- Equal in all races
Signs and symptoms
Café-au-lait spots – just as the name suggests, pigmented brown skin patches. Often occur in the first year of life, grow and increase in number with age, and can be found all over the body. They do not increase the risk of skin cancer.
- Diagnosis requires ≥6 spots of >155 diameter (post puberty) or >5mm (pre-puberty)
Neurofibromas – diagnosis requires ≥2 of any type, or ≥ 1 plexiform. They usually occur in late childhood. Some patients may only have a small number, whilst other have thousands. They come in four types:
- Cutaneous – soft fleshy lumps found all over the body
- Sub-cutaneous – harder and nodular
- Nodular plexiform – usually involve the spinal roots, and grow through the intervertebral foramen where they may be palpable as dumbbell tumours. They can cause spinal cord compression. They may cause parasthesia when pressed
- Diffuse plexiform –
- Both types of plexiform nodule are rarely able to become malignant
Freckling – typically occurs in the axillary and inguinal areas, although any skin fold may be affected. Usually present by the age of 10.
≥ 2 Lisch nodules – these are small nodules on the iris. Usually regular, ≤ 2mm diameter and brown, 90% of patients have them by age 6. Best seen with a slit lamp.
- There are several bone lesions characteristic of neurofibromatosis, including subperiosteal bone cysts, scoliosis, thinning of the long bones, pseudarthrosis and absence of the greater wing of the sphenoid bone – which can result in a pulsating exophthalmos.
1st degree relative with NF1
Learning disability – usually mild, but is relatively common
Compression due to neurfibromas:
- Nerves – compression
- Gut – obstruction, ↑risk of bleeds
- Hypertension – can be due to renal artery stenosis, or more rarely phaechromocytoma
- Malignancy – occurs in 5%. Can be an optic glioma, or malignancy of a neurofibroma (plexiform)
- Epilepsy – risk is very slightly increased
- There is no curative treatment. Symptomatic neurofibromas are often removed, or in some cases, treated neurologically. Often removal of non-cutaneous lesions can be difficult as it results in loss of the nerve at the site of the lesion.
- Many patients have hundreds of cutaneous lesions. It is not possible or practical to remove them all. Particularly troublesome lesions can catch on clothes and other items and should be removed. Often more will continue to grow throughout a patient’s life.
- Genetic counselling should be given to all patients. If one parent is affected, the risk is 50% (autosomal dominant – although in reality risk may be lower due to variable penetrance)
Type 2 Neurofibromatosis – NF2
- Autosomal dominant
- Gene on chromosome 22
Epidemiology and Aetiology
- Much more rare than NF1: affects 1 in 35,000 individuals
Bilateral vestibular schwannomas – can be seen on CT/MRI, but often present with bilateral sensorineural hearing loss in patients aged <30. The schwannomas are actually a form of acoustic neuroma. They may also affect balance and cause facial weakness. The tumours themselves are benign but can cause compression, and increase intra-cranial pressure (ICP).
1st degree relative with NF2 AND, either:
- Unilateral vestibular schwannoma, or
- One of:
- Menningioma – occur in 45% of patients, sometimes several are present.
- Juvenile cataract – aka – Juvenile posterior subcapsular lenticular opacity – usually is the first sign to occur. Can be useful to screen those with 1st degree relatives.
Survival from diagnosis – typically 15 years
No curative treatment
Management based around screening – for the presence of the disease in at risk patients, and for tumours (particularly schwannomas) is those with known disease
- Annual hearing tests are useful as a screening tool. Any patients with abnormalities should have an MRI.
- Surgery should be used to remove schwannomas, but carries a risk of facial weakness and hearing loss.
- No disease present at age 20 (on MRI) implies low risk (for offspring as well as patient). If no disease present at 30 (on MRI) then you can almost guarantee the gene hasn’t been inherited (but, be wary of a family history of late onset disease!)