These studies are carried out to diagnose problems of the nerves and muscles, such as amyotrophic laterals sclerosis (ALS), polymyositis, peripheral neuritis, diseases of the nerves of the neck and back, herniated disc, spondylosis, nerve injury, and nerve entrapment. Nerve conduction study (NCS) and electromyography (EMG) can confirm, locate, and measure the severity of disease.