Neurophysiological testing : Electromyogram

Diagnostic tests Medical history and physical examination Radiological texting Neurophysiological testing Electromyogram Evoked potentials Blood tests Other diagnostic tests

What it is:

It consists of registering the electrical muscle activity. Muscle contracture is due to an electrical discharge of the nerve that controls a particular muscle. If the nerve is affected, its functions are impaired and the characteristics of electrical impulses change. Also, variations in these impulses differ according to whether the nerve is diseased or compressed. Impulse variations may also be different depending on the grade of compression.

What it allows:

EMG is used to evaluate the status of the nerves that control muscles, permitting detection of very light grades of compression or nerve injury.

Risks:

It is usually a painful test, and its use should be recommended only when it is necessary to establish a diagnosis or when therapy is conditioned to EMG outcome.

Indications:

Some of the existing recommendations based on scientific evidence advise the use of EMG in patients with pain of more than 3 or 4 weeks duration, and in those with suspicion of a slight nerve dysfunction, which cannot be detected by a physical examination.

Although the existing recommendations, based on scientific evidence, fail to give these explicit recommendations, it might be wise to perform an EMG in:

1. Patients, with concurrent diseases. For example, a poorly controlled diabetic patient of long standing, who shows nerve dysfunction ("diabetic neuropathy") and who, also, has a disc herniation with apparent nerve root compression. By means of a physical examination, the clinician may discover that the nerve root is not functioning correctly but the EMG may discriminate between what is attributable to diabetes and to disc herniation.

2. Patients with spinal stenosis. In these patients, bone deformation gradually and slowly compresses nerve structures. If this disorder progresses, it may be necessary to operate on the patient. However, surgery is aggressive and this type of patient is usually of older age, so clinicians must be certain of the need for surgery before operating. In these cases, EMG may be useful to evaluate the degree of dysfunction and, if repeated in 3 months, determine if the stenosis is progressing or not.

3. 3. In medical-legal settings, in cases where it is necessary to objectively prove the presence of a disorder. It is very difficult to prove presence of pain, since the patient could simulate it, but an EMG alteration proves in an objective manner the presence of any grade of neurological dysfunction. In this sense, it is important to emphasize that if the EMG is normal it does not completely rule out limiting back pain.