WS7.5. Neuromuscular ultrasound of the lower extremities

Abstract

Neuromuscular ultrasound is rapidly evolving as an excellent diagnostic tool in the evaluation of peripheral neuropathies, especially so in focal neuropathies. It can be of use in understanding the underlying pathological mechanism of neuropathies. Focal neuropathies are more likely to be associated with structural abnormalities that can be easily recognized by imaging modalities. Certain subtypes of polyneuropathies are also associated with morphological changes. Point of care ultrasound helps with rapid examination of long segments of multiple nerves in the out-patient setting. This can result in early triaging of patients and rapid management decisions. Other advantages include easy patient tolerability when compared to nerve conduction studies and lower cost. The sonographic abnormalities that are commonly associated with neuropathies include focal or diffuse enlargement, hour-glass constriction, change in neural architecture, decreased mobility of the nerve and increased vascularity of the nerves. It can also be of use in detecting extra-neural abnormalities like tenosynovitis, soft tissue tumors, entrapment or compression from metallic implants. Peripheral nerves of the lower extremities that can be commonly assessed by sonographic studies include the sciatic, peroneal and tibial nerve. Other less common nerves that are assessed include the lateral femoral cutaneous nerve, the superficial and deep peroneal nerves and the sural nerves. It can also be of value in the evaluation of the digital nerves in the feet. Clinical conditions where sonographic studies can be of paramount importance include evaluation of the peroneal nerve at the fibular head in patients presenting with foot drop and assessment of the tibial nerve in the tarsal tunnel in those presenting with unilateral foot numbness. Its use as a diagnostic tool has extended beyond focal neuropathies to include polyneuropathies secondary to metabolic, inherited and inflammatory causes. Other uses of lower extremity ultrasound include its role as a tool in guiding with therapeutic interventions like steroid injections and detection of morphological changes within cutaneous nerves prior to consideration of nerve biopsy.