Clinical neurophysiology: EEG, nerve conduction studies, EMG and what to expect

Clinical neurophysiology measures electrical signals produced by the nervous system and muscles. Doctors cannot always tell by examination alone where a problem lies, for example whether numbness comes from a nerve at the wrist, a root in the neck or a more general neuropathy. Neurophysiology tests help locate and characterise the problem.

The specialists are consultant clinical neurophysiologists, who are doctors with training in neurology or medicine and then specialist neurophysiology training, supported by clinical physiologists and neurophysiology technologists who perform most routine tests. Results are reported by a consultant or an experienced reporting clinician and sent to the referrer.

Some departments also deal with intraoperative monitoring, in which nerve and brain signals are tracked during spinal or brain surgery, but most patients meet the service as outpatients.

The NHS describes EEG as a test that records electrical activity in your brain, mainly used for epilepsy but also for sleep conditions and encephalitis. Small silver discs are attached to your scalp with sticky paste and connected to a recording machine. You may be asked to open and close your eyes, breathe deeply or look at a flashing light while the recording is made.

The NHS says the test is painless and usually takes about an hour. You can usually eat and drink as normal, and the NHS advises arriving with clean, dry hair with no products in it. Other types include sleep EEG, sleep-deprived EEG, which may mean you cannot drive afterwards, and ambulatory EEG, where you wear a portable recorder.

A normal EEG does not rule out epilepsy, and a minor abnormality does not prove it, so doctors read the result together with the story of what happened.

Nerve conduction studies use small electrical pulses delivered through stickers on the skin to measure how quickly and strongly nerves carry signals. Electromyography (EMG) records electrical activity from a muscle, usually through a fine needle electrode, to see whether the muscle or the nerve supplying it is affected. The two are often performed in the same session.

They are used for carpal tunnel syndrome, peripheral neuropathy, nerve root problems, nerve injuries, muscle diseases and conditions such as motor neurone disease and myasthenia gravis. The NHS says tests that check how well your nerves are working are used when motor neurone disease is suspected.

The electrical pulses feel like quick tingles or taps and the needle can be uncomfortable for a short time. You can usually go home and carry on as normal. Tell the staff if you take blood thinners, have a pacemaker or have a bleeding disorder.

• Visual, auditory and somatosensory evoked potentials, which check conduction along sensory pathways.

• Repetitive nerve stimulation and single-fibre studies for myasthenia gravis and related conditions.

• Video telemetry, where EEG is recorded with video over days to capture and classify seizures or non-epileptic attacks.

• Sleep studies and tests of autonomic function in some centres.

• Intraoperative monitoring during spine and brain surgery, performed by the neurophysiology team in theatre.

NHS neurophysiology is usually accessed through a GP or hospital consultant, with urgent slots for suspected conditions such as Guillain-Barré syndrome or rapidly progressive weakness. Waiting times for routine tests can be long in some areas, which is a common reason people consider private testing.

Private neurophysiology is available through hospitals and some independent clinics, often with a neurologist consultation first. Ask who will report the test, whether a consultation to explain the result is included in the fee, and how the report will be sent to your GP. A test done in isolation, without clinical context, is harder to interpret.

• Wash your hair and do not use gel, wax or hair products before EEG; remove weaves, braids or wigs if you can, as the NHS advises.

• Keep your skin free of creams and lotions on the limb being tested for nerve studies, and wear loose clothing so arms or legs can be exposed.

• Take your usual medicines unless told otherwise, and bring a list, including blood thinners.

• Arrange a lift home if you have been asked to stay awake the night before an EEG.

• Bring a witness account or video of attacks if the test is for seizures.

Neurophysiology is a planned service and is not an emergency route. Call 999 for a first seizure, a seizure lasting more than 5 minutes, sudden weakness in the face, arm or leg, slurred speech, or sudden severe headache. Get urgent help from NHS 111 or an urgent GP appointment for rapidly worsening weakness, difficulty swallowing or breathing, or loss of bladder or bowel control.