Neurophysiology

Neurophysiology or Electrodiagnostic Testing

Neurophysiology, or electrodiagnostic testing, involves specialised investigations used to diagnose and predict outcomes in disorders of the peripheral nervous system. These tests are performed by a specialist doctor known as a neurophysiologist, who is trained in interpreting the results and guiding treatment decisions. There are two main techniques:

1. Nerve Conduction Studies (NCS)
2. Electromyography (EMG)

Objectives of Neurophysiology

• To localise the site of a nerve lesion
• To characterise the nature of the nerve lesion
• To quantify the extent of nerve damage
• To prognosticate the likely outcome of a nerve injury

Nerve Conduction Studies (NCS)

Nerve conduction studies measure how fast and efficiently a nerve transmits impulses, evaluating both sensory and motor nerves.

During the test, surface electrodes are attached to the skin, using either stick-on or Velcro pads. A pulse-emitting electrode is placed over the nerve to be tested, sending brief electrical pulses that feel like a buzzing sensation, which is typically not too uncomfortable. A recording electrode picks up the impulses conducted by the nerve. By measuring the time it takes for the impulse to travel between the electrodes and the distance between them, the conduction velocity can be calculated. The machine also measures the amplitude (size) of the transmission wave.

NCS is a safe, well-tolerated procedure.

Electromyography (EMG)

EMG assesses the condition of a muscle and the motor neuron (nerve cell) controlling it. In a needle EMG, a fine needle electrode is inserted into the muscle to detect electrical signals. The neurophysiologist observes for spontaneous activitywhen the muscle is at rest and measures electrical activity during slight and maximal muscle contraction. Some minor bruising may occur at the insertion site, which usually resolves within a few days.

Preparing for NCS/EMG

• Inform your neurophysiologist if you have a cardiac pacemaker or are taking blood-thinning medications such as aspirin, clopidogrel, or warfarin.
• Let your neurophysiologist know if you have a bleeding disorder.
• Take a bath or shower beforehand and avoid applying lotions or creams.

Interpretation of Results

It’s important to understand that neurophysiology results are not absolute, and false positives or negatives can occur. For example, some patients may present with symptoms but have normal test results, while others may show abnormal findings despite being asymptomatic. Therefore, neurophysiology should only be requested with a specific clinical question in mind, allowing any abnormal results to be interpreted within the relevant clinical context.

Key Message

• Neurophysiology is an extension of clinical assessment and should never replace careful history-taking and physical examination.
• Communication between the surgeon and the neurophysiologist is essential for meaningful interpretation of test results.