Sciatica symptoms that fail to resolve within six weeks or that worsen require medical attention. Patients should seek medical attention if they experience sudden, severe pain, numbness or muscle weakness in the back or leg. Other symptoms that may require a visit to a physician include pain that follows a traumatic injury or trouble controlling the bowels or bladder.

In diagnosing sciatica, a physician will review the patient's medical history and perform a physical examination. Special attention will be paid to the spine and legs, with testing to check muscle strength and reflexes. Tests that are likely to reveal the presence of sciatica include walking on toes or heels, rising from a squatting position (to test the strength) and lying on one's back and raising the legs one at a time straight up into the air (called the straight leg raise test).

The patient may be asked to complete a pain assessment form. Imaging tests may be performed to help identify the cause of sciatic nerve compression or to help rule out other potential causes of symptoms. These tests can include:

• MRI (magnetic resonance imaging). Probably the best test for diagnosing sciatica, this test uses powerful magnets and radio waves to produce cross-sectional images of the back. MRI can reveal damage to intervertebral discs and ligaments and the presence of tumors.

• CAT scan (computed axial tomography). This test produces detailed, cross-sectional images of the body. A contrast medium is sometimes injected into the spinal canal before x-rays are taken to help highlight problem areas. CAT scans can reveal herniated discs and tumors, but they also present risks such as infection and damage to the spinal cord.
  
  
• Spinal x-ray. This test may reveal the presence of narrowed discs (stenosis) or spondylolisthesis.

Tests that can detect damage to the sciatic nerves include:

• Nerve conduction studies. Use electrodes placed on the legs to record the electrical signals of a nerve.
  
  
• Electromyography. A test using needles inserted into leg muscles to measure electrical activity sent from the central nervous system (brain or spinal cord).

Even after all these tests, it may sometimes be difficult to diagnose what is causing sciatica.