An EMG (electromyogram) is to diagnose muscle and/or nerve problems. Tiny needle electrodes are inserted into various muscles to get a readout of activity. If it shows a nerve supply problem, the nerve to that muscle is known. EMG can’t always reveal the cause of the problem, just that it is abnormal, a neuropathy.
Doing and interpreting EMG studies requires special training and is somewhat subjective. It is impossible for a lay person to look at an EMG study and make something out of it. If multiple nerves are involved, it is usually a peripheral neuropathy, which occurs most frequently in diabetics. When imaging studies are not helpful, EMG may point to disease in nerve or muscle.