Nerve Ultrasound as a Diagnostic and Screening Tool in Neurofibromatosis

| Neurology
Johan Telleman, *Leo Visser,

The authors have declared no conflicts of interest.

EMJ Neurol. ;5[1]:44-45. Abstract Review No. AR1.

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Neurofibromatosis Type 1 (NF1) is a condition associated with peripheral nerve pathology. Localised and plexiform NF1 may arise, and malignant transformation of such neurofibromas can occur, which is a major cause of morbidity and mortality.1 However, there is no consensus on screening NF1 patients for this malignant transformation because available techniques, including whole-body magnetic resonance imaging (MRI), are relatively expensive and time consuming.2

Nerve ultrasound is an emerging diagnostic technique in peripheral nerve disease. It is already widely applied in entrapment neuropathy and is a promising adjunctive tool in polyneuropathy and traumatic neuropathy.3 Nerve ultrasound may also have applications as a diagnostic and screening tool in NF1. It allows good qualitative assessment of peripheral nerves, which could make it advantageous as a primary imaging modality in cases of suspected neuropathy in NF1 patients.4,5 In addition, a large spread in sonographic peripheral nerve involvement is observed in NF1.4 A recent pilot study was performed showing some patients had almost no abnormalities, while others had widespread peripheral nerve involvement with multiple plexiform neurofibromas and severe nerve enlargement. Benign tumour load and the presence of plexiform neurofibromas are risk factors for the development of a malignant peripheral nerve sheath tumour (MPNST).6 As large differences between patients were found with nerve ultrasound, it may therefore be useful as a screening tool for MPNST development by identifying a group of NF1 patients at higher risk.

Additional studies will have to be performed to determine the exact role of the technique as a diagnostic and screening tool. It will have to be determined if results are reproducible, how sonographic abnormalities develop over time, and under which circumstances nerve ultrasound is useful; currently, a follow-up study is being performed to address several of these issues.

Neurofibromatosis Type 2 (NF2) is a condition characterised by vestibular schwannomas and other intracranial tumours.7 However, peripheral nerve involvement can also occur in this disease.8 Two recent small studies on nerve ultrasound even showed the presence of schwannomas of the peripheral nerve in 80–100% of patients.5,9 Therefore, clinicians should take into account peripheral nerve tumours in their differential diagnosis of sensory loss and loss of strength in NF2.

Recent studies have shown that nerve ultrasound can adequately visualise peripheral nerves in neurofibromatosis and that abnormalities are frequent in this condition. Further studies will have to be performed to determine the exact value of this new technique. Nonetheless, nerve ultrasound seems a promising diagnostic and screening tool in neurofibromatosis.

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