Electrodiagnosis

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Introduction

Electrodiagnosis refers to the measure of the electrical activity in nerves and muscles to identify or obtain information about a disease or disorder. It comprises mainly of electromyography (EMG) and nerve conduction study (NCS). Less commonly used electrodiagnostic testing includes somatosensory evoked potentials (SSEP), single fiber EMG (SFEMG), and repetitive stimulation. (textbook) In physiotherapy practice, electrodiagnosis can be performed by a clinical electrophysiologic certified specialist. Electrodiagnostic testings can be used to evaluate conditions such as Peripheral neuropathy, Entrapment neuropathy (including carpal tunnel syndrome, ulnar neuropathy at the elbow, peroneal (aka fibular) neuropathy at the fibular head, tarsal tunnel syndrome), Brachial plexopathy, Lumbosacral plexopathy, Cervical or lumbosacral radiculopathy, Spinal stenosis, Neuromuscular junction disorders (myasthenia gravis, Lambert–Eaton syndrome), Myopathies Disorders of the anterior horn cell. (textbook)

Electromyography

Electromyography (EMG) involves the evaluation and recording of muscle activity. The instrument for Electromyography is the Electromyograph. The electomyograph detects electrical potential generated by a muscle and produces a record of the muscle activity called electromyogram. EMG is used as a diagnostics tool for identifying neuromuscular diseases, or as a research tool for studying kinesiology, and disorders of motor control. EMG signals are sometimes used to guide botulinum toxin or phenol injections into muscles. EMG signals are also used as a control signal for prosthetic devices such as prosthetic hands, arms and lower limbs. (Wikipedia) EMG is usually performed with nerve conduction study.

The electrical activity of a muscle can be measured using a surface electrode (surface EMG), for a large region of muscle, and a needle EMG for a lesser region.

The surface EMG, while it gives a good indication of which muscle groups are active in for example tremor or dystonia, gives little information as to the fine structure of those muscles. (fund. Of Electromyography Roger Graham Whittaker)

The needle EMG involves the insertion of a (sterile) needle into the muscle to measure electrical potential in the muscle. Muscles are usually tested at rest and minimal muscle contraction. (textbook)

It is imperative that the patient is told to expect, and the test should be discontinued if the patient becomes uncomfortable or requests that the testing should be stopped.

Limitations

1. Adipose tissue can affect the recordings of a surface EMG.
2. Surface EMG can measure only superficial muscles.
3. Needle EMG involves voluntary activation of muscles, so can be less effective in unresponsive/uncooperative patients, paralyzed patients, children and infants.

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