Neurophysiological tests assess the function of the brain and nervous system. They measure normal and abnormal electrical impulses in the brain (Electroencephalogram or EEG) or electrical signals through nerves and their response in muscles. In patients with spinal conditions the most common tests are nerve conduction studies (NCS), electromyography (EMG) and spinal cord monitoring. The latter is performed during surgery.
Nerve Conduction Studies (NCS)
This test measures how fast a nerve impulse travels from one point to another along the nerve. The test is a measure of the speed and effectiveness with which nerves in the arms and legs send messages to the muscles or from the skin to enable you to move and feel. If there is a blockage due to pressure on a nerve the test can say how severe the pressure and where the blockage is. It is commonly used in the arm to look for carpal tunnel syndrome or ulnar nerve syndrome. No needles are involved but some discomfort can be experienced when the nerve is stimulated. There is no risk of damaging the nerve from the stimulation.
Nerves or nerve roots which have been under pressure or are involved in other disease processes give abnormal signals to the muscles they supply. This can be picked up by tiny needles placed in the muscles. The insertion of the needles can be uncomfortablealthough rarely causes real pain. In patients with spinal conditions this test is used to identify the nerve roots which are under pressure (radiculopathy). It is helpful in the neck and lower back if it is not clear from the clinical examination and MRI scan which nerve root is causing the symptoms.
Spinal Cord Monitoring
This is used during surgery to monitor the function of the spinal cord. During certain operations it is important for the surgeon to know whether damage is being done. This usually applies to scoliosis surgery or tumours of the spinal cord. Most other spinal operations can safely be done without it.