This is a clinical vignette highlighting the role of ultrasound in the EMG lab. A 45-year-old mechanic presents with a history of very suggestible ulnar neuropathy, although it could also be a C8 radiculopathy. The nerve conduction studies show normal median motor and sensory responses, a low amplitude ulnar motor response with some slowing of conduction velocity, but no focal conduction block or focal slowing, and the ulnar sensory response is also low amplitude and greater than 50% reduced compared to the other side. EMG showed occasional fibrillation potentials and neurogenic motor unit changes in the first dorsal interosseous, normal findings in EIP and FPL, so other C8 non-ulnar innervated muscles, also normal findings in the proximal ulnar muscle, flexor kappa ulnaris. So the EMG diagnosis was a non-localizable ulnar neuropathy, hence we elected to perform ultrasound. So on the left here, you can see the ulnar nerve is here. It's sitting beneath this aponeurosis that forms between the two heads of the flexor kappa ulnaris muscles, and we measured the cross-sectional area at 0.1 square centimeters. We then measured it a little more proximally in the retrocondylar groove between the medial epicondyle and the olecranon, and it's a lot larger, it's twice as big, 0.2 square centimeters, and this is a long axis view, which shows a significant change in morphology here at the area of focal swelling consistent with ulnar neuropathy, and that diameter of 0.4 centimeters is enlarged. So we were able to make a diagnosis of ulnar neuropathy localizing to the level of the medial epicondyle by using clinical neurophysiology and ultrasound together. And this did help with prognosis, you can usually manage these conservatively and expect a good recovery when the problem is at the level of the medial epicondyle. Had we found the compression at the level of the cubital tunnel just distal to the medial epicondyle beneath the two heads of the flexor kappa ulnaris muscles, then the prognosis is less favorable and you would be more inclined to refer this patient for a surgical opinion. So the ultrasound was really quite complementary in this case.

ulnar neuropathy

C8 radiculopathy

nerve conduction studies

EMG

ultrasound

ncs

nmus

sono

US

electromyography