(Kiosk 1) Isolated Left Radial Neuropathy and F-wave Studies

Case Diagnosis: Isolated left radial neuropathy

Case Description or Program Description: A 56-year-old muscular male presented with left arm pain and spasms for five years. Initial spasms were in the triceps and spread to the shoulder. He had pain and numbness that radiated down the back of the arm to the hand. Physiatric evaluation revealed left scapular muscle atrophy. Previous electrodiagnostic study was interpreted as cervical radiculopathy and ulnar entrapment neuropathy. MRI of the cervical spine and chest were negative for pathology.

Setting: Tertiary care electrodiagnostic laboratory

Assessment/Results: The electrodiagnostic evaluation revealed more than 45% attenuation of radial sensory nerve and compound muscle action potential amplitudes, slow CV between spiral grove and elbow with polyphasic MUPs and no abnormal spontaneous activity in the anconeus, brachioradialis, and extensor carpi ulnaris but not in triceps. An F-wave study of the radial nerve demonstrated a prolonged minimum latency with A-waves. These findings suggested demyelinative and axon loss lesion in the left radial nerve between the spiral groove and anconeus. The likely area of compression of radial nerve is between the lateral brachialis and the medial brachioradialis.

Discussion (relevance): F-wave studies are used to examine conduction between distal stimulation sites and the spinal cord and are useful in diagnosing demyelinating peripheral neuropathy. This case helps demonstrate the utility of F-wave studies along with routine conduction studies in teasing out possible location of focal neuropathy and differentiating from radiculopathy, in conjunction with needle studies.

Conclusions: Delineating between focal neuropathy and radiculopathy is an important aspect of electrodiagnostic studies. Demyelinating lesions of the radial nerve can be confirmed with the addition of F-wave studies where they are not typically done.