EMG and Nerve Conduction Study (NCV)

It starts with tingling in your fingers at night, and then you start dropping cups. For someone else it's burning feet that feel like cotton wool, years after a diabetes diagnosis. Symptoms like these point to the nerves, but not to where the damage is or how bad it is.

Nerve conduction studies (NCV) and electromyography (EMG) answer that. For nerve conduction, small electrical pulses are passed along a nerve through stickers on the skin, and the machine measures how fast and how strongly the signal travels. For EMG, a fine needle records the electrical activity of a few muscles. Together they show whether the problem lies in a nerve, a nerve root in the spine or the muscle itself, and how severe it is.

The tests can be normal in the first 2 to 3 weeks after a nerve injury, and they miss damage limited to the smallest nerve fibres.

These studies are part of the diagnostic services in our neurology department, where neuropathy caused by diabetes is regularly managed.

For each nerve, the report gives the speed (conduction velocity), the size of the signal (amplitude) and the delay (latency). Slowing at one spot, such as the wrist, suggests compression there, and carpal tunnel syndrome is graded mild, moderate or severe. Small signals along whole nerves suggest loss of nerve fibres, as in most diabetic neuropathy.

Mild carpal tunnel often settles with a night splint, while severe compression may need a small operation. Neuropathy leads to tests for causes such as diabetes, low vitamin B12 or thyroid problems. A pinched nerve root usually needs an MRI and, if it doesn't improve, sometimes surgery such as a discectomy.