Neurocutaneous Syndromes

Neurocutaneous syndromes are genetically determined disorders that combine distinctive skin manifestations with central nervous system involvement. This reflects the shared embryological origin of skin and nervous system from the ectodermal germ layer.

The group includes neurofibromatosis type 1 (the commonest), neurofibromatosis type 2, tuberous sclerosis complex, and Sturge-Weber syndrome, among several rarer conditions.

Each carries a characteristic, though variable, pattern of cutaneous, neurological, and associated systemic manifestations. They need structured, lifelong, multidisciplinary surveillance, because of direct disease-related complications and, in several, an increased risk of specific associated malignancy.

Classification and pathophysiology

• Neurofibromatosis type 1 is an autosomal dominant condition caused by mutations in the NF1 gene, which encodes neurofibromin, a tumour suppressor protein. It is the commonest neurocutaneous syndrome.
• It is characterised by café-au-lait macules, neurofibromas, axillary and inguinal freckling, and Lisch nodules (iris hamartomas).
• A proportion of affected individuals develop optic pathway glioma and other associated tumours. Specific skeletal abnormalities and learning difficulty are also more likely.
• Neurofibromatosis type 2 is a distinct condition caused by mutations in a different gene, NF2, which encodes merlin. It is characterised principally by bilateral vestibular schwannomas, the defining and essentially pathognomonic feature when bilateral.
• The risk of meningioma and spinal ependymoma is also increased. It is genetically and clinically distinct from neurofibromatosis type 1 despite the similar name.
• Tuberous sclerosis complex results from mutations in either the TSC1 or TSC2 gene. Both encode proteins involved in regulating the mTOR signalling pathway.
• It is characterised by hamartomatous growths in multiple organ systems. Characteristic skin findings are hypomelanotic macules, facial angiofibromas, and shagreen patches.
• Central nervous system involvement includes cortical tubers and subependymal giant cell astrocytomas. The latter carry a specific risk of obstructive hydrocephalus because they typically lie near the foramen of Monro.
• Incidence of epilepsy and autism spectrum disorder is substantially increased. Renal angiomyolipomas and cardiac rhabdomyomas also occur.
• Sturge-Weber syndrome generally occurs sporadically rather than through inherited transmission, reflecting a somatic, post-zygotic mutation.
• It is characterised by a facial capillary malformation (port-wine stain, typically in the ophthalmic division distribution of the trigeminal nerve) with an ipsilateral leptomeningeal vascular malformation.
• This produces a risk of seizures and glaucoma and, over time, progressive neurological impairment, reflecting chronic cerebral hypoperfusion related to the vascular malformation.

• Neurofibromatosis type 1 presents with café-au-lait macules. They are typically the earliest apparent feature, often present from infancy. Their number and size carry diagnostic significance under established criteria.
• Axillary or inguinal freckling develops somewhat later in childhood.
• Neurofibromas include cutaneous lesions and plexiform neurofibromas, which have a potential for significant morbidity. Plexiform neurofibromas can cause significant disfigurement and, in a small proportion of cases, undergo malignant transformation to malignant peripheral nerve sheath tumour.
• Lisch nodules are identifiable on formal ophthalmological slit lamp examination.
• Optic pathway glioma occurs in a meaningful proportion of children with neurofibromatosis type 1 and most commonly presents in early childhood. It may be asymptomatic, identified only through proactive surveillance, or present with visual impairment, proptosis, or, where the tumour involves the hypothalamic region, precocious puberty.
• This warrants structured ophthalmological surveillance throughout early childhood.
• Neurofibromatosis type 2 typically presents in adolescence or early adulthood with symptoms of bilateral vestibular schwannoma: progressive sensorineural hearing loss, tinnitus, and balance disturbance.
• A proportion of affected individuals have additional features reflecting the associated meningioma or spinal ependymoma risk.
• Tuberous sclerosis complex frequently presents in infancy with infantile spasms or other seizure types, reflecting the cortical tuber burden.
• Hypomelanotic macules are often the earliest identifiable cutaneous feature and are sometimes best seen using Wood lamp examination. Facial angiofibromas and shagreen patches typically develop somewhat later in childhood.
• Cardiac rhabdomyomas are occasionally identified antenatally or in early infancy. They are sometimes the first clue prompting diagnosis of the broader underlying condition.
• Sturge-Weber syndrome presents at birth with the characteristic facial capillary malformation.
• Seizures follow, typically in infancy, reflecting the underlying leptomeningeal vascular malformation. Over time there is a progressive risk of glaucoma.
• These features need structured, ongoing surveillance. Glaucoma needs proactive ophthalmological surveillance, particularly where the capillary malformation involves the periocular region.

• Diagnosis of neurofibromatosis type 1 is clinical, based on established diagnostic criteria that require a specific combination of the characteristic features.
• Genetic testing is available to support confirmation. It is particularly relevant in atypical or incomplete presentations, and for family cascade screening and reproductive counselling.
• Neurofibromatosis type 2 diagnosis relies on magnetic resonance imaging demonstrating bilateral vestibular schwannomas. Genetic testing supports confirmation and family screening.
• Tuberous sclerosis complex diagnosis uses established clinical criteria based on characteristic major and minor features across the affected organ systems, together with genetic testing.
• It requires structured evaluation: magnetic resonance imaging of the brain (identifying cortical tubers and screening for subependymal giant cell astrocytoma), renal ultrasound (screening for angiomyolipoma), and dermatological assessment.
• Echocardiography is particularly relevant in infancy, because cardiac rhabdomyomas characteristically regress spontaneously over the first years of life.
• Sturge-Weber syndrome diagnosis is supported by the characteristic facial capillary malformation together with magnetic resonance imaging demonstrating the leptomeningeal vascular malformation.
• The extent of leptomeningeal involvement correlates with the risk and severity of neurological complications.
• Ongoing surveillance according to established, published guidelines specific to each condition is an essential, standard part of long-term management across this group.
• It combines periodic clinical assessment with targeted imaging and other investigation directed at the recognised complications of that condition.

• Management is directed at the individual manifestations present. It is delivered through coordinated multidisciplinary care incorporating neurology, dermatology, and ophthalmology.
• Add specialists where relevant to the condition: audiology and neurosurgery for neurofibromatosis type 2, and nephrology for tuberous sclerosis complex because of the renal manifestations.
• Selumetinib, a MEK inhibitor, is a relatively recent targeted advance for symptomatic, inoperable plexiform neurofibroma in neurofibromatosis type 1. It gives meaningful tumour volume reduction and symptomatic benefit in appropriately selected patients.
• This is a significant development for a previously difficult-to-treat manifestation.
• Manage optic pathway glioma in neurofibromatosis type 1 with watchful waiting for asymptomatic, stable lesions, because these tumours characteristically behave indolently in this context. Use chemotherapy for progressive, symptomatic disease.
• Avoid surgical resection and radiotherapy where possible, or use them with particular caution, because of additional recognised risks in this population.
• Manage vestibular schwannoma in neurofibromatosis type 2 by observation for smaller, stable, or asymptomatic tumours. For larger or progressive tumours, use surgical resection, stereotactic radiosurgery, or, increasingly, bevacizumab, an anti-angiogenic agent with specific efficacy in this context.
• Individualise the approach carefully, given the bilateral nature of the condition and the importance of preserving hearing where possible.
• Everolimus, an mTOR inhibitor, directly targets the molecular pathway disrupted in tuberous sclerosis complex. It is a specific targeted treatment for subependymal giant cell astrocytoma and renal angiomyolipoma, and benefits the associated epilepsy in some patients.
• Seizure management follows standard antiepileptic principles and is an important component in both tuberous sclerosis complex and Sturge-Weber syndrome.
• Vigabatrin is a specifically effective agent for infantile spasms in tuberous sclerosis complex.
• Consider surgical epilepsy treatment, including resection of a well-localised epileptogenic tuber, for appropriately selected, medically refractory cases.
• Ophthalmological management includes structured glaucoma surveillance and treatment in Sturge-Weber syndrome. Laser therapy can treat the facial capillary malformation. It addresses cosmetic concerns but does not alter the associated neurological risk.
• Proactive surveillance for the ophthalmological manifestations relevant to each condition is an important component of management.
• Lifelong multidisciplinary surveillance following established, condition-specific guidelines is essential.
• Offer family genetic counselling on inheritance pattern and recurrence risk. Neurofibromatosis type 1, neurofibromatosis type 2, and tuberous sclerosis complex are predominantly inherited, each with autosomal dominant inheritance. Sturge-Weber syndrome is predominantly sporadic.
• Provide psychosocial support for the substantial, ongoing impact of these chronic, multisystem conditions on the affected individual and their family.