What is an EMG?

An EMG is an electrical test of peripheral nerves and skeletal muscle. By convention EMG refers to both the nerve test (NCV) and the muscle test (EMG). NCV may be performed by a physician or by a technician under direct supervision by a physician. EMG involving a needle puncturing the skin can be performed only by a licensed physician.

NCV: "Nerve conduction velocity" measures how fast nerve impulses travel in myelinated motor and sensory nerves. The nerve being studied is stimulated with a special probe on the skin directly over the nerve. Responses are recorded by a computer that calculates the speed of nerve conduction and the size of the evoked motor or sensory response. Over forty years of medical research has established normal values for each nerve response.

EMG: An "electromyogram" measures electrical activity in skeletal muscles by insertion of a tiny pin electrode directly into the muscle. Electrical stability of the muscle and the configuration of individual motor units is assessed and recorded. An experienced electromyographer is able to recognize pathology related either to disease of muscle itself or abnormal changes due to damage to nerve roots or peripheral nerves innervating a specific muscle.

I cannot reiterate enough the importance of performing EMG and NCV together to provide a more accurate assessment of a patient's medical condition. Technicians performing NCV without EMG and without the direct supervision of a qualified physician electromyographer are practicing bad medicine for several reasons. Take the example of radicular neck or low back pain- NCV does not diagnose radiculopathy. If you see a report claiming otherwise the report is fraudulent and the technician is incompetent. Radiculopathy is diagnosed by EMG only.

NCV without EMG also cannot quantify the severity of axonal damage to muscle in peripheral neuropathies due to either focal entrapment (for example, CTS) or to generalized peripheral axonal neuropathy (for example, diabetic or alcoholic neuropathy). Conversely, EMG without NCV may miss co-morbid conditions: my research studies in large pain populations reveal that 23-25% of patients with referred neck or back pain have CTS or peripheral neuropathy.