443 - Middle Trunk Brachial Plexus Lesion Due To Diabetic Amyotrophy

Case Diagnosis: Right sided middle trunk brachial plexus lesion due to diabetic amyotrophy

Case Description: A 57-year-old male with a history of uncontrolled type two diabetes mellitus presented to sports medicine clinic with atraumatic right shoulder pain for one year. Symptoms included stabbing pain along the medial right scapula, numbness in the medial right forearm, and occasional right cervical neck pain. Manual muscle testing revealed 4/5 strength in the right wrist extensors, elbow extension, forearm pronation, and with shoulder protraction. Reflexes were diminished bilaterally in the biceps and wrist extensors, with an intact triceps reflex. The abduction tension release sign on the right provided mild symptom relief. A electromyography and nerve conduction study (EMG/NCS) revealed a brachial plexus lesion. A significant reduction in sensory nerve action potentials (SNAP) amplitudes, particularly in the affected arm, strongly suggested plexopathy rather than radiculopathy. Needle EMG revealed denervation in C6-C7 innervated muscles. However, the absence of needle EMG in pre-plexus muscles limits our ability to completely exclude radiculopathy.

Discussions: Brachial plexopathies and cervical radiculopathies often present similarly in the upper limbs yet distinguishing between them is essential due to differences in management and prognosis. Radiculopathies involve nerve roots, leading to reduced compound muscle action potential (CMAP) amplitudes without significant conduction velocity changes, and preserved SNAPs. In contrast, brachial plexopathies affect both motor and sensory fibers post-ganglionically, resulting in reduced CMAP and SNAP amplitudes. EMG and NCS are critical in differentiating these conditions.

Conclusions: Diabetic amyotrophy, though more commonly affecting the lower limbs, can also present as brachial plexopathy. It involves immune-mediated vascular injury, leading to ischemia of the nerves, and is more likely to occur in patients with uncontrolled diabetes, as seen in this case.