Introduction

Neurofibromatosis (NF) encompasses a group of genetic disorders characterised by the development of tumours, known as neurofibromas, on nerves throughout the body. These tumours arise in various tissues, including peripheral nerves, the spinal cord, and the brain, leading to neurological complications. One of the most significant consequences of neurofibromatosis is nerve damage, which can result in pain, sensory deficits, motor dysfunction, and other neurological deficits. 

Causes of neurofibromatosis

Neurofibromatosis occurs due to mutations in specific genes that regulate cell growth and proliferation in the nervous system. The two main types of neurofibromatosis, NF1 and NF2, are each associated with distinct genetic alterations.

NF1, also known as von Recklinghausen disease, is caused by mutations in the NF1 gene,¹ located on chromosome 17q11.2. The NF1 gene encodes the protein neurofibromin, which functions as a tumour suppressor by inhibiting cell proliferation and regulating cellular signalling pathways. Mutations in the NF1 gene lead to dysfunctional neurofibromin, resulting in uncontrolled cell growth and the formation of neurofibromas.

NF2, on the other hand, is caused by mutations in the NF2 gene located on chromosome 22q12.2. The NF2 gene encodes the protein merlin ( schwannomin), a must in cell-cell adhesion, cytoskeletal organisation, and growth factor signalling. Loss of functional mutations in the NF2 gene disrupts normal cellular processes, causing tumours, like vestibular schwannomas, within the central nervous system.

Symptoms of neurofibromatosis

The clinical manifestations of neurofibromatosis vary widely depending on the type and severity of the disease. Common symptoms² of NF1 include café-au-lait spots (pigmented skin lesions), cutaneous neurofibromas (benign tumours of peripheral nerves), Lisch nodules (hamartomas of the iris), skeletal abnormalities, and learning disabilities. In addition to these characteristic features, individuals with NF1 may experience complications related to nerve damage, such as neuropathic pain, sensory deficits, and motor dysfunction. In severe cases, neurofibromas may undergo malignant transformation, leading to the development of malignant peripheral nerve sheath tumours (MPNSTs), which carry a poor prognosis.

In contrast, NF2 manifests bilateral vestibular schwannomas (acoustic neuromas), which arise from the vestibular portion of the eighth cranial nerve. They cause sensorineural hearing loss, tinnitus, imbalance, facial weakness, and other neurological deficits as they grow and compress adjacent structures within the internal auditory canal. In addition to vestibular schwannomas, individuals with NF2 may develop other central nervous system tumours, including meningiomas, ependymomas, and spinal schwannomas, further exacerbating neurological complications.

Diagnosis of neurofibromatosis

Neurofibromatosis is diagnosed by clinical evaluation, family history, and genetic testing.³ Diagnostic criteria for NF1 include the presence of at least two of the following features: six or more café-au-lait spots, two or more cutaneous neurofibromas, axillary or inguinal freckling, optic glioma, two or more Lisch nodules, distinctive bony lesions, or a first-degree relative with NF1. In individuals suspected of having NF2, the diagnosis is established based on the presence of bilateral vestibular schwannomas, or a family history of NF2 plus one of the following: unilateral vestibular schwannoma, two or more non-vestibular tumours (e.g., meningioma, schwannoma, glioma), or a first-degree relative with NF2 and a unilateral vestibular schwannoma.

Genetic testing⁴ plays a crucial role in confirming the diagnosis of neurofibromatosis and identifying specific mutations in the NF1 or NF2 genes. Molecular genetic testing can help differentiate between NF1 and NF2 and provide valuable information for genetic counselling and family planning. Additionally, imaging studies, such as magnetic resonance imaging (MRI) and computed tomography (CT) scans, may be performed to assess the extent of tumour involvement and monitor disease progression in individuals with neurofibromatosis.

Treatment of neurofibromatosis

The management of neurofibromatosis focuses on symptom relief, tumour control, and preservation of neurological function. Treatment strategies may vary depending on the type and severity of the disease, and individual patient factors.

Surgical resection is often the primary treatment modality for symptomatic neurofibromas and vestibular schwannomas. The surgical intervention aims to remove tumours causing neurological deficits, alleviate pain, and improve the quality of life for affected individuals. However, surgery may be associated with risks, including nerve damage, loss of function, and tumour recurrence, particularly in cases of NF1 where tumours can be extensive and multifocal.

In cases where surgical resection is not feasible or tumours are unresectable, alternative treatment modalities may be considered. Radiation therapy, including stereotactic radiosurgery and fractionated radiotherapy, can target and shrink tumours while minimising damage to surrounding healthy tissue. However, radiation therapy may be associated with long-term side effects, including radiation-induced neuropathy and secondary malignancies, necessitating careful consideration of risks and benefits.

Chemotherapy is another option for managing neurofibromatosis, particularly in individuals with aggressive or recurrent tumours. Chemotherapeutic agents, such as vincristine, carboplatin, and etoposide,  alone or in combination inhibit tumours and improve clinical outcomes. However, chemotherapy may be associated with adverse effects, including cytotoxicity, myelosuppression, and gastrointestinal toxicity, requiring close monitoring and supportive care.

Emerging molecular therapies offer promising avenues for treating neurofibromatosis by targeting specific signalling pathways involved in tumour growth and proliferation. In NF1, inhibitors of the mitogen-activated protein kinase (MAPK) pathway, such as selumetinib⁵ and trametinib, have shown efficacy in reducing tumour size and improving clinical outcomes in patients with inoperable plexiform neurofibromas. Similarly, drugs targeting vascular endothelial growth factor (VEGF) signalling, such as bevacizumab, have demonstrated benefits in reducing tumour vascularity and ameliorating symptoms in individuals with NF2-associated vestibular schwannomas.

Summary

Neurofibromatosis is a complex genetic disorder characterised by the development of tumours on nerves throughout the body, which can lead to nerve damage and associated neurological complications. The two main types of neurofibromatosis, NF1 and NF2, are each associated with distinct genetic mutations and clinical presentations. While NF1 primarily affects the peripheral nervous system, NF2 predominantly involves the central nervous system, particularly the cranial and spinal nerves. The diagnosis of neurofibromatosis is based on clinical evaluation, family history, and genetic testing, with molecular genetic testing playing a crucial role in confirming the diagnosis and guiding treatment decisions. Neurofibromatosis management requires a multidisciplinary approach to address the neurological and systemic manifestations of the disease. Surgical resection remains the primary treatment modality for symptomatic tumours. Alternative therapies are radiation therapy, chemotherapy, and targeted molecular therapies, which may be considered for unresectable or recurrent tumours. Emerging therapies targeting specific signalling pathways offer promising avenues for the personalised management of neurofibromatosis and improving patient outcomes.

Overall, a better understanding of the pathophysiology of nerve damage in neurofibromatosis and advances in treatment modalities are essential for optimizing clinical care and improving the quality of life for individuals affected by this debilitating condition.