True sciatica is caused by irritation of the sciatic nerve or one or more of its component nerves which branch off from the lower spinal cord in the low back. These component nerves join together in the pelvis to form the sciatic nerve which then runs down the back of each leg. In most cases of true sciatica, the cause is a herniation or bulge of one of the lower discs in the spine.

Another cause of sciatica symptoms is a condition known as piriformis syndrome. The piriformis is a muscle that runs from the sacrum in the lower spine to the hip, and it can sometimes create pressure on the sciatic nerve. In addition, in some cases the piriformis can develop knots of contraction called trigger points which may produce pain referral into the buttock and leg which closely mimics sciatic nerve irritation and may be misdiagnosed as true sciatica.

Sciatica symptoms can be diagnosed through various means. A doctor can often get a pretty good idea about the cause of sciatica symptoms through physical examination, but usually an MRI or CT scan is ordered to more fully evaluate the discs and other possible causes of sciatica. Imaging studies may also be done using special dyes to get better quality images of the discs, nerves, and other tissues for a more thorough evaluation.

In some cases, electrodiagnostic testing through procedures like EMG (electromyography) and/or NCV (nerve conduction velocity) may be performed to evaluate the condition of the nerve and find out the extent of any nerve damage that may be present.

In cases where diagnostic testing does not show any abnormalities with the sciatic nerve itself, the piriformis must then be suspected as the primary symptom generator.

Once diagnostic testing has determined the cause of sciatica symptoms, then the most appropriate plan of treatment can be implemented and there is a much better chance of recovery.