Neurofibromatosis

Historically, descriptions of individuals thought now to have neurofibromatosis (NF) have been found in manuscripts dating back to 1000 AD. Von Recklinghausen coined the term 'neurofibroma' in 1881 to describe a benign tumour arising from the peripheral nerve sheath. Consequently, type 1 neurofibromatosis (NF1) is also known as Von Recklinghausen's disease.

Introduction

NF is a genetic disorder causing lesions in the skin, nervous system and skeleton.

The neurofibromatoses are autosomal dominant genetic disorders that encompass the rare diseases NF1, NF2, and schwannomatosis:¹

• Type 1 is the more common form and caused by a defect in the gene, NF1, situated at chromosome 17q11.2:²

  • Neurofibromin, the gene product, is a ubiquitous nervous system protein and is believed to act as a tumour suppressor.

  • Loss of neurofibromin leads to an increased risk of developing benign and malignant tumours but effects of a mutation are highly variable between sufferers and can appear at any age due to a variety of mutations, differing penetration and mosaicism.

  • Watson's syndrome is the only subtype of NF1 to have a uniform phenotype in families and is characterised by pulmonary stenosis, cognitive impairment, café-au-lait patches and few cutaneous neurofibromas.

• Type 2 is a central form with CNS tumours rather than skin lesions:

  • There are inherited schwannomas (vestibular tumours), typically bilateral, but also meningiomas and ependymomas.

  • The implicated mutation is on chromosome 22 at gene locus 22q12.2.

• Schwannomatosis is a recently recognised form of neurofibromatosis, characterised by multiple non-cutaneous schwannomas, that is an histologically benign nerve sheath tumour:³

  • Patients with schwannomatosis overwhelmingly present with pain, and pain remains the primary clinical problem and indication for surgery.⁴

  • Surgical resection may result in a good outcome.⁵ However, surgical resection has a risk of nerve injury, pain may persist after removal of the tumour(s) and tumours may regrow at the same site.¹

Epidemiology⁶

Both type 1 and type 2 NF are inherited as autosomal dominant conditions but, for both types, there is no family history in about 50%, reflecting the incidence of new mutations.

• Neurofibromatosis type 1 makes up about 96% of all neurofibromatosis cases. Prevalence is 1 in 3,000 births.⁷ It occurs equally between gender and races. Fifty percent of patients have a spontaneous mutation, and the other half have an inherited mutation. There is a 100% penetrance with variable expressivity.

• Neurofibromatosis type 2 makes up about 3% of all cases and has a prevalence of around 1 in 33,000 births.⁸ There is no gender or race predilection. Neurofibromatosis type 2 has variable presentations amongst different families. A more severe clinical presentation is associated with a frameshift or a nonsense mutation that results in a truncated protein.

• The prevalence of schwannomatosis is difficult to assess given the clinical similarities to NF2 and lack of a reliable genetic test in all cases, although it is speculated to be about as common as NF2.⁹

Presentation¹⁰

The major NF1-associated tumour is the neurofibroma. In addition, clinical manifestations include bone dysplasia, learning disabilities and an increased risk of malignancy.

NF2 includes schwannomas of multiple cranial and spinal nerves, especially the vestibular nerve, as well as other tumours such as meningiomas and ependymomas.

The schwannomatosis phenotype is limited to multiple schwannomas, and usually presents with pain.

Diagnostic criteria for NF1⁷

There are diagnostic criteria for NF1 that require at least two of seven criteria. Some of these do not appear until later childhood or adolescence, and so confirmation of the diagnosis may be delayed and children should be followed up:

• At least six café-au-lait spots or hyperpigmented macules. They must be at least 5 mm wide in children younger than 10 years and 15 mm in adults.

• Axillary or inguinal freckles.

• Two or more typical neurofibromas or one plexiform neurofibroma.

• Optic nerve glioma.

• Two or more iris hamartomas. They are called Lisch nodules and are seen by slit-lamp examination.

• Sphenoid dysplasia or typical long-bone abnormalities such as arthrosis.

• Having a first-degree relative with NF1.

Diagnostic criteria for NF2¹¹

At least one of the following three is required for diagnosis of NF2:

• Bilateral 8th nerve masses on MRI scan.

• A first-degree relative with NF2 for a unilateral 8th nerve mass.

• A first-degree relative with NF2 for an individual with at least two of the following:

  • Meningioma

  • Glioma

  • Schwannoma

  • Juvenile cataracts

Diagnostic criteria for Schwannomatosis⁹

Currently, the diagnosis can be made on a molecular or clinical basis. Clinically the criteria are:

• At least two nondermal biopsy-proven schwannomas with no radiographic evidence of bilateral vestibular schwannomas on high-quality magnetic resonance imaging; or

• One biopsy-proven nondermal schwannoma or intracranial meningioma and a first-degree relative with schwannomatosis.

• It has also been proposed that a patient with two or more nondermal tumours that are suspicious for schwannomas, but without histological confirmation, be considered 'possible' for a diagnosis of schwannomatosis.

• Finally, as bilateral vestibular schwannomas of NF2 may occur in the third decade of life, an age cutoff of at least 30 years may be employed to ensure an accurate diagnosis of schwannomatosis.

Dermal features

• Café-au-lait spots are often the first findings in NF1. They may be present at birth or may appear with time. They usually increase in size and number during childhood. 1-2 café-au-lait patches occur in 10% of the general population. Children with 3-5 café-au-lait patches, but no other signs of NF1, should be followed up, as they might have mosaic NF1 or NF2.

• Axillary or inguinal freckles are rare at birth but appear throughout childhood and adolescence.

• Café-au-lait patches and skin-fold freckling do not usually cause complications; however, some patients are distressed by the appearance of this pigmentation and may be helped by skin camouflage advice. There is no evidence to support the routine use of laser treatment for café-au-lait patches.

• Hypopigmented macules may co-exist with café-au-lait spots in NF1 and are found in a similar distribution.

• Urticaria pigmentosa may be seen in a small subset of infants. It is a collection of mast cells within the dermis.

• Naevus anaemicus and benign cherry angiomas (Campbell de Morgan spots) are observed more frequently in NF1 than in the general population.

• Juvenile xanthogranulomas are benign orange papules that appear transiently on the head and trunk in 1% of young children. The suggestion of an increased risk of chronic myeloid leukaemia in children with NF1 and xanthogranulomas has not been borne out and routine haematological testing is not recommended in this group.

Neurofibromas

• They may be in the skin or subcutaneous tissues. Deep lesions may require palpation for detection but cutaneous lesions may appear initially as small papules on the trunk, extremities, scalp, or face.

• Cutaneous neurofibromas are found in the majority of NF1 individuals, are rare in early childhood but tend to develop in the late teens or early twenties. There may be an increase in numbers and a growth of existing lesions at puberty or in pregnancy.

• Cutaneous neurofibromas rarely appear to undergo malignant transformation. However, they may catch on clothing and/or cause cosmetic embarrassment, stinging or itching.

• Subcutaneous neurofibromas may be tender to touch and cause tingling in the distribution of the affected nerve. Malignant change occasionally occurs: if rapid growth occurs, refer to a specialist, as removal may result in nerve damage.

• Plexiform neurofibromas have malignant potential.⁶ There is an 8% to 13% risk for plexiform neurofibromas to develop into malignant peripheral nerve sheath tumours. This should be suspected if there is a pain for more than one month, new neurological deficits, change of the neurofibroma from soft to hard, or rapid increase in size. These malignancies are treated with wide local excision. Imatinib has been shown to decrease plexiform neurofibroma size.

• In NF2, sensorimotor polyneuropathy may be seen and there may be identifiable tumours along the relevant peripheral nerves.
  

Ocular problems

• Tumours of the optic nerve (gliomas) occur in about 15% of children with NF1.¹²

• They are often asymptomatic but, over time, tumours may cause visual acuity loss, abnormal colour vision, visual field loss, squint, pupillary abnormalities, pale optic disc, proptosis and hypothalamic dysfunction. Risk is highest in those aged under 7 years. Young children rarely complain of early visual impairment and sometimes it is not picked up until it is advanced, with bilateral visual loss. Parents should be aware to look out for potential indicators of problems - failure to pick up small toys or bumping into things.

• The most common presentation is asymmetrical visual field defects. Optic nerve gliomas occasionally start to cause symptoms in older children or even adults. They can also undergo spontaneous regression.

• Lisch nodules are usually only seen by slit lamp. Occasionally, they can be visible via the ophthalmoscope.

• Patchy choroidal abnormalities and corkscrew retinal vessels are sometimes seen in patients with NF1.

• In NF2, posterior subcapsular or juvenile cataracts can precede CNS symptoms. These cataracts may progress over time, impairing visual acuity. Some have retinal hamartomas or epiretinal membranes that are not always significant to vision.

Skeletal problems

• Sphenoid dysplasia usually causes no problem but can cause herniation through the bony defect. Patients with plexiform neurofibroma of the eyelid or temporal region often have ipsilateral sphenoid dysplasia.

• Congenital pseudoarthrosis may be apparent at birth. Bowing of the tibia is the most common presentation and occurs in about 2% of those with NF1. Thinning and angulation of long bones with prominence of the anterior tibia and progressive deformity can occur throughout early childhood. Bowing of the forearm is less common. Fracture can occur spontaneously or after trivial injury, and NF should be considered as a differential for non-accidental injury.

• The thoracic cage may be asymmetrical with flaring or prominence of the inferior ribs. It affects some children with NF1 but rarely requires surgical correction.

• Scoliosis may occur with or without kyphosis. This may become evident in childhood or adolescence and adolescent girls are affected rather more often than boys. If it starts before the age of 10 years, scoliosis has a poor prognosis and is likely to be rapidly progressive. Scoliosis detected in adolescence should be followed, but is less likely to require orthopaedic intervention.

• NF1 causes disruption of bone maintenance and reduced bone mineral density. Be vigilant about the possibility of osteoporosis.

Neurological problems

• Neurological complications develop from tumours and malformations, including aqueduct stenosis. Skull deformity due to sphenoid wing dysplasia can lead to pulsating exophthalmos.

• Intracranial meningiomas are diagnosed in 45–58% of individuals with NF2, and spinal meningiomas are diagnosed in approximately 20%.¹³

• Severe scoliosis can deform the spine, causing cord compression and respiratory compromise.

• Pressure on peripheral and spinal nerves and the spinal cord will also have neurological sequelae.

• Epilepsy is usually mild and only occurs in 6-7% of NF1 individuals.

• Carotid artery stenosis/occlusion and cerebral aneurysm may occur with NF1.

• Patients should be advised to seek urgent help where they experience acute or progressive sensory disturbance, motor deficit and inco-ordination or sphincter disturbance, which may indicate an intracranial lesion or spinal cord compression.

• Cognitive problems are the most common neurological complication and usually present as an IQ in the low average range. Specific learning problems occur in one to two thirds of children with NF1. The cause of cognitive problems in NF is not known. Children and adolescents with NF are more likely to have attention deficit hyperactivity disorder (ADHD); incidence is high, at around 40%.¹⁴

Cardiovascular problems

• Congenital heart disease (pulmonary stenosis and hypertension) are associated with NF.

• Renal artery stenosis occurs in approximately 2% of those with NF1, so NF should be a diagnosis considered in hypertensive children, young adults and pregnant women, and refractory hypertension in older individuals and those with an abdominal bruit.

• Phaeochromocytoma similarly occurs in approximately 2% of those with NF1. About 12% of these tumours are malignant.

Other clinical problems/complications may include:

• Respiratory - pulmonary manifestations of NF1, which usually include bilateral basal reticulations and apical bullae and cysts, are reported in 10-20% of adult patients.⁷

• Gastrointestinal (GI) - abdominal bloating, pain, dyspepsia, haemorrhage and constipation may suggest a GI neurofibroma. Carcinoid tumours may give rise to facial flushing, diarrhoea, right-sided cardiac lesions, facial telangiectasias and bronchoconstriction. GI stromal tumours are also associated with NF1 and may present with anaemia and GI bleeding.

• Psychological - disfigurement and the unpredictable course of NF may cause anxiety and depression. Parents of children with NF1 report a profound impact of NF on physical, social, behavioural and emotional aspects of their quality of life.¹⁵ Children with NF1 can have difficulties forming friendships and developing social skills.¹⁶

• Endocrine - precocious puberty occurs in about 3% and is associated with tumours of the optic chiasma.¹⁷

• Obstetric - there appears to be an increased risk of perinatal complications in NF1, with a higher stillbirth rate, intrauterine growth restriction and caesarean section rate. During pregnancy, neurofibromas may grow in size and number and there is the risk of cord compression if spinal plexiform neurofibromas expand. Obstetricians should also ensure pelvic neurofibromas do not impede delivery of the baby.
  

Investigations

NB: baseline brain and spinal MRI scanning and routine imaging of the chest and abdomen to identify asymptomatic tumours do not influence management and are not advised.¹⁸

Plain X-ray

• Dural ectasia is often seen on X-rays of the vertebral column. It may suggest future progressive scoliosis.

• X-rays are required if:
  

  • There are possible modelling defects of the long bones or ribs.

  • There is concern that a bony lesion may be adjacent to a plexiform neurofibroma.

  • Scoliosis is seen on clinical examination.

  • Bone pain exists.

Scans

CT or MRI scanning may be required:

• MRI is preferred for diagnostic head imaging. Hyper-intense lesions on T2-weighted brain MRI are probably caused by aberrant myelination or gliosis and are pathognomonic of NF1. They occur most commonly in children aged 8-16 years but tend to have disappeared by adulthood. They are associated with cognitive impairment. The presence of these lesions can assist in diagnosing NF1 but MRI under anaesthetic is not warranted for this purpose in young children.¹⁸

• Consider CT or MRI scans to check ventricular size if head circumference in an infant is increasing rapidly. Hydrocephalus is rare in NF1.

• MRI can evaluate the optic nerves or optic chiasma. It is indicated for optic nerve pallor, visual changes, proptosis, or precocious puberty.

• Consider MRI scans of the head if headaches increase in frequency or intensity over time. Brain tumours are more common in NF2 than in NF1.

• MRI can also be useful to evaluate mediastinal masses, spinal cord tumours, deep plexiform neurofibromas, abdominal and pelvic lesions and neurofibromas of the brachial or sacral plexus.

Electrophysiology

• If seizures occur, electroencephalography (EEG) is required in assessment.

• Myelography is occasionally helpful to clarify the extent of a spinal cord tumour but, generally, MRI alone is enough.

• Visual evoked potentials (VEPs) may be helpful in detecting optic nerve gliomas or assessing tumour progression with optic pathway tumours.

Slit-lamp examination

This usually requires the expertise of an ophthalmologist:

• Slit-lamp examination may provide essential diagnostic information in older children and adults who present with only one clinical criterion such as multiple café-au-lait spots.

• The frequency of Lisch nodules increases with age. They are seen in more than 95% of those with NF1 who are older than 10 years.

• Slit-lamp examination is valuable to decide if the parents of an affected child carry the NF1 mutation, even in the absence of any other features of the disease.

Genetic testing

NF1 mutational analysis may clarify the diagnosis in some ambiguous cases but is not advocated routinely.¹⁹

Histology

Biopsy of asymptomatic cutaneous neurofibromas should not be undertaken for diagnostic purposes in individuals with clear-cut NF1.

Hearing tests

Tests for hearing and vestibular function are important in NF2.

Differential diagnosis

Type 1 or type 2 NF?

• Type 1 tends to present in childhood or adolescence, whilst type 2 usually presents in adults aged under 40 years, and mostly in the 20s.

• Around 45% of type 2 present with hearing problems such as deafness and tinnitus, with or without loss of balance or facial weakness due to vestibular schwannomas.

• Café-au-lait spots are the usual, early feature of NF1 but there are rarely more than six spots in NF2. It rarely shows axillary or inguinal freckles.

• Multiple subcutaneous lesions can be indistinguishable between the two.

• Posterior subcapsular lenticular opacities, even in childhood, would be suggestive of NF2, whereas Lisch nodules would be diagnostic of NF1.

Other conditions with café-au-lait patches include:

• McCune-Albright syndrome.

• DNA repair syndromes.

• Hereditary non-polyposis cancer of the colon.

Other conditions with pigmented macules include:

• Neurocutaneous melanosis.

• Peutz-Jeghers syndrome.

Other localised overgrowth syndromes include:

• Klippel-Trénaunay syndrome.

• Proteus' syndrome.

Management

Care is largely a matter of monitoring progress and intervening appropriately where tumours produce pressure symptoms or behave in a manner suggestive of malignant change.

Neurofibromatosis type 1

• Cafe-au-lait spots and neurofibromas are benign and do not require treatment.

• Surgical excision can be performed on symptomatic lesions, but recurrence can occur.

• Plexiform neurofibromas developing into malignant peripheral nerve sheath tumours should be treated with wide local excision. Imatinib has been shown to decrease plexiform neurofibroma size.

• Monitoring for any neurological changes and referral to a neurologist are paramount. These changes can be due to tumour development. Consistent ophthalmological evaluation is recommended for observation of the development of optic gliomas. Chemotherapy is the treatment of choice for optic gliomas.

• Monitoring children for difficulty learning and behavioural issues is important. Counselling can be beneficial for patients to provide support regarding the disease's autosomal dominant inheritance pattern.

Neurofibromatosis type 2

• These patients require assessment of their hearing. Ophthalmology evaluation, MRI, audiology, and brainstem evoked potentials are important in managing these patients.

• Surgery is still the first-line treatment for symptomatic tumours, but there is a 44% recurrence rate. Radiation can be used, but there is increased the risk of malignant transformation.

• Bevacizumab, a VEGF inhibitor, is a monoclonal antibody and can be used to treat neurofibromatosis type 2 patients medically. It decreased tumour size in 53% of cases and improved hearing in 57%.⁸

• Patients with suspected neurofibromatosis type 2 should have an MRI of the head and spine done. Getting thin cuts through the internal auditory canals is important. Treatment is done if the tumour is compressing on the brainstem or preventing hearing loss.

• All children with uncomplicated disease should be assessed annually, ideally by one paediatrician in each area to facilitate co-ordinated care. Young adults (16-25 years) will need education about NF and its possible complications, including reproductive counselling.

Schwannomatosis¹

• The current management for pain is either surgery or medication for pain relief.

• Tumours seen in schwannomatosis are often more complicated than the sporadic schwannomas and so need specialist care to ensure successful resection while minimising the risk of nerve injury.

• Although resection frequently results in dramatic improvement in pain, the more tumours resected, the less effective is surgery for pain control.

• There have been some anecdotal reports that a secondary form of whole body pain develops, especially after a patient has been through multiple tumour resections.

Older adults should be offered the opportunity of attending clinic on an annual basis:

• Adults with severe disease will usually already have been identified by this stage and need lifelong monitoring in a dedicated specialist clinic.

• Those with mild disease have a much lower risk of complications, but should have a minimum of annual blood pressure checks and be aware to consult their GP (who can refer them on if necessary) if they encounter unusual symptoms.

Medication

Additional medication may be needed for secondary problems such as hypertension, epilepsy or ADHD.

Surgery

Neurofibromas

• Neurofibromas that press on vital structures, obstruct vision, or grow rapidly need urgent attention.

• Plexiform neurofibromas can be difficult. They often recur after resection because there are residual cell rests deep in soft tissues.

• Neurofibromas on the scalp, along the hairline, or around the waist where clothes rub can cause irritation and discomfort and are worthy of removal.

• In NF2, there has been some success with cochlear implants for bilateral acoustic neuroma.²⁰

Spinal cord tumours

• Prompt attention is required if neurological symptoms appear. Resection of spinal cord tumours is quite difficult but may be necessary to prevent progressive paraplegia or quadriplegia.

• For some patients, surgical intervention may not cure but it provides valuable palliation.

Orthopaedic surgery

• Rapidly progressive scoliosis or severe bony defects need urgent attention.

• Early referral for scoliosis gives the best results.

• Long-bone defects can require amputation but mode bracing and casting techniques have reduced the need.

Vascular surgery

• Percutaneous transluminal renal artery angioplasty (PTRAA) may be effective in treating some renal artery stenosis due to fibromuscular dysplasia.

• Others may require surgical repair and anastomosis of the renal artery.

Complications

• Individuals with NF are at an increased risk of brain tumours, leukaemia, and other malignancies of neural crest origin, including neurofibrosarcomas.²²

• Brain tumours are rather more common in NF2.

• Occasionally, peripheral nerve sheath tumours undergo malignant change in NF1 but not NF2.

• Malignant peripheral nerve sheath tumours are the main soft tissue malignancy associated with NF1. These tumours are known to occur at high frequency and lead to poor survival.²³

Prognosis

• Type 1, in particular, is so varied in its manifestation, that it is difficult to predict outcome, as phenotype is so variable even within affected families.

• Most people with NF1 lead relatively long and healthy lives, but it does reduce life expectancy.²⁴

• NF2 generally has a worse prognosis. Much of the morbidity from these tumours results from their treatment. Early detection and prompt attention to complications may reduce overall morbidity and mortality.

Prevention¹⁸

The risk of an affected individual with NF1 or NF2 transmitting the disease to their child is 50% but this cannot predict the severity of any inherited disease. When the complications that cause lifelong morbidity or early mortality in NF1 are considered, the risk of having a severely affected child is about 1 in 12.

Where parents have had the first affected child known in a family, both parents should be examined for cutaneous stigmata or Lisch nodules. They may be found to have a segmental or mosaic form of NF and thus be at risk of having another affected child. Where there are no clinical signs, their affected child's condition will have arisen due to a de novo mutation, and the risk to the parent of having another child with NF1 is extremely small (less than 1%).

The NF1 gene mutation can now be found in 85-95% of cases. Prenatal testing is possible using fetal DNA extracted from chorionic villous sampling or from amniocentesis. Many do not want prenatal assessment because it cannot determine disease severity. Pre-implantation genetic diagnosis is also available. Genetic counselling prior to conception should be advised in all individuals with NF.