233 - Brachial Plexus Ultrasonography of Neuralgic Amyotrophy Localized to the Upper Trunk

Neuralgic amyotrophy (NA) with associated ultrasonographic findings of an enlarged upper trunk of the brachial plexus.

Case Description:

A 51-year-old male presented with left arm weakness and atrophy. The weakness was preceded by neck pain that radiated towards the periscapular region 1 month following C3-5 anterior cervical diskectomy and fusion. Examination revealed painless, profound weakness, atrophy, and loss of fine touch sensation within the left deltoid, biceps brachii, and brachioradialis muscles. Needle electromyography (EMG) showed ongoing denervation and markedly reduced recruitment of large, complex motor unit potentials in the left upper trunk brachial plexus distribution. Neuromuscular ultrasonography (NMUS) demonstrated diffuse enlargement of the left upper trunk of the brachial plexus compared to the asymptomatic contralateral side (upper trunk cross-sectional area 21.5 mm² vs 8 mm²). Brachial plexus MRI later confirmed this finding with T2 hyperintensity isolated to the left upper trunk. The clinical history, EMG, NMUS, and MRI confirmed the presence of NA confined to the left upper trunk.

Discussions:

Neuralgic amyotrophy is characterized by subacute, severe pain followed by marked weakness and atrophy. It is often first recognized clinically and supported by EMG. NMUS provides value allowing for direct visualization of peripheral nerves and brachial plexus. Pathognomonic changes observed with NMUS include focal fascicular or nerve enlargement, fascicular entwinement, and torsion. In the brachial plexus, inflammation results in marked focal enlargement. NMUS allows for precise localization of plexus lesions, isolating the primary nerve segment involved.

Conclusions:

NMUS provides clinically vital diagnostic information in NA that may not be as readily detected by EMG alone and is more easily obtained compared to MRI.