(Kiosk 3) An In-depth Look at Post-trauma Lower Trunk Brachial Plexopathy: A Case Report

Case Diagnosis: A 61-year-old male with post-trauma lower trunk brachial plexopathy and concurrent bilateral carpal tunnel syndrome.

Case Description or Program Description: The patient presented with left-hand weakness and intermittent numbness in both hands following a fall on his left elbow three months prior. Nerve Conduction Study (NCS) and Electromyography (EMG) were completed suggesting mild left and severe right carpal tunnel syndrome, respectively.

At 2-month follow-up, the patient presented with improved sensation in both hands, but weakened left grip strength and persistent left elbow pain. Physical exam of the left upper extremity revealed 4/5 strength with wrist extension and of the extensor indicus proprius (EIP), interossei, and abductor pollicis brevis (APB) muscles. On EMG, the left EIP, first dorsal interossei (FDI) and APB revealed decreased recruitment. The left extensor carpi radialis (ERCB) was normal. NCS results were unchanged, and additionally, the medial antebrachial cutaneous (MAC) nerve was normal.

Setting: Outpatient PM&R clinic.

Assessment/Results: The patient was diagnosed with a left lower trunk brachial plexopathy due to trauma. Despite an affected EIP, a posterior interosseous nerve (PIN) lesion was ruled out due to a normal ECRB. While the APB and FDI were affected, a medial cord lesion was ruled out due to an affected EIP, which suggested a lower trunk lesion given radial nerve involvement. The results of a left elbow and shoulder MRI were non-contributory.

Discussion (relevance): This case illustrates an atypical presentation of a lower trunk brachial plexus injury following trauma and displays how a lower trunk lesion can be distinguished from a medial cord or PIN lesion.

Conclusions: Due to conservation of the MAC nerve, we demonstrated the diagnosis of an atypical left lower trunk brachial plexopathy caused by trauma. Typically, the involvement of the MAC nerve is specific for lower trunk lesions. Although NCS testing revealed this nerve to be normal, we attributed this finding to fascicular sparing.