Neurophysiological Diagnostics
Introduction
Spinal nerve roots and radiculopathy
Upper extremities
Nerve conduction studies. Nerve conduction studying are used to determine if nerve damage is present on motor and sensory neurons. A stimulating and recording electrode are placed over a nerve (e.g. the Ulner or Median nerve). The time it takes for the impulse to reach the recording electrode is termed the latency. Latencies are on the order of milliseconds. The conduction velocity is calculated by dividing the distance between the electrodes by the latency, which equals the conduction velocity.
Lower extremities
The bulbocavernosus reflex or Osinski reflex can be monitored to test for S2-4 nerve root function. The bulbocavernosus reflex is a reflex arc. The dorsal nerve (a branch of the pudendal nerve) carries sensory information from the genitals to the spinal cord via S2-4 nerve roots. Some fibers of the dorsal nerve synapse onto interneurons of the spinal cord that make synaptic connections with motor neurons that innervate the bulbocavernosus muscle, causing the rectum to contract. This pathway can be monitored by placing stimulating electrodes along the sensory nerve of the genitals and recording electrodes on the rectum.
Spinal cord and myelopathy
Signs of cervical myelopathy include a positive Hoffman's sign, Babinski reflex, clonus sign, finger escape sign, or Lhermitte's sign. Individually, none of these signs can be used as a sole predictor of myelopathy, but they do provide evidence to make a diagnosis.
1. Hoffman's sign is a reflex test that is an involuntary movement of the thumb or index finger when the nail of the middle finger is flicked. It is a sign of upper motor neuron disease.
2. Lhermitte's sign is produced by neck movement or forward flexion, causing a transient feeling of electric shock down the spine or extremities.
3. Clonus sign
Signs of cervical radiculopathy include a positive shoulder abduction test. This test is done by putting the hand of the patient above the shoulder, usually above the head, which will relieve the pain.