A nerve conduction study measures how fast and how strongly electricity travels along a nerve. It is a test of NERVE FUNCTION, not a picture.
Two things are worth knowing before you read your result.
- A normal study does not rule out a compressed nerve.
- And a severe-looking study does not automatically mean surgery.
The test informs the decision. It does not make it.
What actually happens
Two parts, and people are usually only warned about the first.
- Nerve conduction. Small electrical pulses on the skin, recording how long the signal takes to travel a known distance. Uncomfortable, like repeated static shocks, over in minutes
- EMG. A fine needle into selected muscles, listening to their electrical activity at rest and on contraction. This is the part that tells you whether a muscle has lost its nerve supply, and it is sorer than the first part
Cold hands slow conduction. If your hands were cold, say so — it affects the numbers.
The three numbers that matter
- Latency. How long the signal takes to arrive, in milliseconds. Prolonged latency means the insulation around the nerve is damaged. This is the earliest change in compression, and the most recoverable
- Conduction velocity. Speed, in metres per second. Slowing across a specific segment localises the compression — slowing across the elbow rather than along the forearm points straight at cubital tunnel
- Amplitude. The size of the response. Reduced amplitude means nerve fibres have been lost, not just slowed, and that is the number with prognostic weight. Latency recovers quickly after decompression. Amplitude recovers slowly, and sometimes not fully
On the EMG side, terms like fibrillations and positive sharp waves mean a muscle is sitting there without a working nerve supply. Reinnervation changes describe a nerve that is growing back.
Slowed is irritated. Smaller is damaged. Those two words carry most of the prognosis in the report.
What the test misses
This is the part that causes the most confusion.
- Mild or intermittent compression. A meaningful minority of people with genuine carpal tunnel have a normal study, particularly early, and particularly when symptoms only happen at night. A normal result does not mean you imagined it
- Small sensory nerve branches that are difficult to test reliably — see Wartenberg’s syndrome
- Dynamic compression that only happens in certain positions, such as thoracic outlet syndrome, where studies are often unremarkable
- Timing after injury. Done too early after a nerve injury, the study can look misleadingly normal because the changes take a week or two to appear
- Two problems at once. A neck problem and a wrist problem can coexist, and a clear finding at the wrist doesn’t exclude one higher up. See cervical radiculopathy
Patients arrive quite regularly having been told their normal study means nothing is wrong. Their symptoms are still real, their examination still fits, and the treatment plan usually doesn’t change.
How the result changes the plan
- Mild changes, intermittent symptoms. Splinting, position and activity change. Retest only if things worsen
- Moderate changes. The decision sits with your symptoms and function rather than the numbers
- Reduced amplitude or EMG changes in the muscles. This is the group where waiting has a cost, because fibres already lost are what limit the final recovery. See therapy or surgery
- Normal study, convincing symptoms. Treat the person. See peripheral neuropathy or carpal tunnel if both hands and feet are involved
Practical notes
- No moisturiser on the day — it interferes with the electrodes
- Warm hands. Bring gloves if you are travelling in air conditioning
- Tell them about blood thinners and any pacemaker or implanted device
- Ask for a copy of the numbers, not just the conclusion. A repeat study in a year is only useful if you can compare
The study measures the nerve on the day it was tested. Your symptoms measure the nerve on every other day, and both belong in the decision.
Every article on this site is written using the Closing Window Method: name the window your condition runs on, find where you are in it, and act while it’s still open.