Electrodiagnosis of cervical radiculopathy

Compression may occur at the level of the dorsal (pre-ganglionic) sensory root (which, if occurs alone, produces a sensory-only radiculopathy) and/or at the ventral (motor) root. When motor exam is normal, EMG is unlikely to show abnormality. The American Association of Electrodiagnostic Medicine practice parameter for cervical radiculopathy ^{1) 2) 3)} reports sensitivity of 50-71 % for the needle EMG examination and correlation between positive needle EMG and radiologic findings 65-85 %.

EMG can also be normal in sensory only radiculopathy, which ocasionally occurs in cervical spine, but not in lumbar spine.Since most muscles have at least dual innervation this poses a particular challenge for proximal cervical radiculopathies in which many muscles have the same shared innervation, e.g. biceps,deltoid, brachioradialis, infraspinatus and supraspinatus are all innervated by C5-C6.

The electrodiagnostic examination with needle electromyography is the most important means of testing for radiculopathy. This test has modest sensitivity but high specificity. It complements imaging of the spine. Electromyography in combination with nerve conduction testing is valuable in excluding entrapment neuropathies and polyneuropathy, conditions that frequently mimic radicular symptoms. A streamlined examination with 6 muscles, 1 of which is the paraspinal, has a high diagnostic yield, yet minimizes patient discomfort and examiner time ⁴⁾.

For muscles to demonstrate fibrillation and positive waves there must be axonal loss in the motor nerve axons which innervates a muscle. Muscle demonstrates fibs and positive waves within 1 to 2 weeks following loss of innervation depending on the distance from the nerve to the muscle.

NCV is helpful to asses for peripheral neuropathy which may have symptoms similar to radiculopathy (e.g. carpal tunnel syndrome vs. C6 radiculopathy; ulnar neuropathy vs.C8 radiculopathy).

A good physical exam can differentiate these entities in most cases.

Electrodiagnostic testing is not needed if the diagnosis is clear, but has clinical utility when peripheral neuropathy of the upper extremity is a likely alternate diagnosis.

Needle EMG examination of at least 1 muscle innervated by the C5, C6, C7, C8, and T1 spinal roots in a symptomatic limb, performed and interpreted by a specially trained physician. Cervical paraspinal muscles at 1 or more levels, as appropriate to the clinical presentation, should be examined (except in patients with prior cervical laminectomy using a posterior approach). If a specific root is suspected clinically, or if an abnormality is seen on the initial needle EMG examination, additional studies as follows:

a. Examination of 1 or 2additional muscles innervated by the suspected root and a different peripheral nerve. b. Demonstration of normal muscles above and below the involved root.

2. Guideline: At least 1motor and 1 sensory NCS should be performed in the clinically involved limb to determine if concomitant polyneuropathy or nerve entrapment exists. Motor and sensory NCSs of the median nerve and ulnar nerves should be performed if symptoms and signs suggest CTS or ulnar neuropathy.

If 1 or more NCSs are abnormal, or if clinical features suggesting polyneuropathy are present, further evaluation may include NCSs of other nervesin the ipsilateral and contralateral limbs to define the cause of the abnormalities.

3. Option: If needle EMG examination is abnormal, needle EMG of 1 or more contralateral muscles may be necessary to exclude bilateral radiculopathy, or to differentiate between radiculopathy and polyneuropathy, motor neuron disease, spinal cord lesions, or other neuromuscular disorders.

4. Option: Perform median and/or ulnar F-wave studies in suspected C8 or T1 radiculopathy. Compare with the contralateral side if necessary.

5. Option: Perform cervical nerve root stimulation to help in identifying radiculopathy. 6. Option: Perform H-reflex study of the flexor carpi radialis to assist in identifying pathology of the C6 and C7 nerve roots.