The use of EMG and NCS in neurological disorders
DR. MICHAEL A. MORRIS
Published: May 14, 2013
EMG (Electromyography) is the study of electrical activity of the muscles. NCS (Nerve Conduction Study) is the study of electrical activity of nerves. When combined these tests provide a very effective tool in the diagnosing of neurological disorders. MRI (Magnetic Resonance Imaging), CAT (Computed Axial Tomography) Scans and X-rays are diagnostic tests that look for structural abnormalities in specific body parts. While determining if there is structural damage, these radiology tests cannot determine if the structures are functioning, or how these structures are affecting nerves and muscles, or if they themselves are being affected by the abnormal functioning of nerves or muscles. EMG/NCS is extremely helpful whenever there is possibility of nerve or muscle damage.
The study is conducted in two parts. The NCS is usually performed first by the neurodiagnostic technologist, who test the nerves by applying surface recording electrodes over various muscles or nerves on different parts of the body (e.g. hands, arms, legs and feet). The technologist then stimulates various nerves by using a probe/stimulating electrode that provides a small electrical current to the nerve, which is then measured and recorded. This small electrical stimulus can be compared to the sensation of a static shock felt from rubbing your body on a carpet or touching a refrigerator. The speed, shape, height and pattern of the electrical response of the nerves provides information on whether or not the nerves are injured and where the injury is located.
The second part of study is usually performed by a physician with specialized training in Neurophysiology/Neurodiagnostics after reviewing the NCS. The physician uses a small recording needle electrode, very similar in size to an acupuncture needle, which he inserts through the skin into various muscles that receive nerve supply from different nerves or spinal nerve roots. The needle electrode is connected to a machine, with an oscilloscope that records the electrical activity. This electrical activity also generates sounds that allows the doctor to both listen and see the electrical activity of the muscles at rest and during muscle contraction. While some find it uncomfortable, the more relaxed the patient is, the easier it is to tolerate the needle exam.
The entire study is then analyzed by the physician trained in neurophysiology who generates a comprehensive report, presenting objective findings and stating if the study is normal or abnormal and if possible, the likely site(s) of the injury.
This study looks very specifically at muscles and nerves. Some of the more common medical conditions which benefit from EMG/NCS testing include carpal tunnel syndrome, cervical radiculopathy (pinched nerve in the neck), low back pain, spinal injury, sciatica, traumatic nerve injury (e.g. gunshot or motor vehicle accidents) along with numbness and tingling of the feet. Some more severe but not as common conditions include ALS (Amyotrophic Lateral Sclerosis), Myopathy (muscle disease which can be congenital or acquired) and Guillain-Barre syndrome to name a few.
The EMG/NCS has been and continues to be a very important diagnostic test that helps in the management of neurological disorders to not only diagnose, but also to evaluate the effectiveness of various treatment options.
• Michael A. Morris is a neurodiagnostic technologist with 25 years in the field, who has training in EEG, Evoked Potentials, IOM and NCS. He became an American board-certified EDT (Electro-Diagnostic Technologist) in 1995. He relocated from Henry Ford Hospital in Detroit, Michigan in 2000. He is the Neurodiagnostic lab manager at the Bahamas Neurological Center.