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Tests and diagnosis
By Mayo Clinic staffTo help diagnose sciatica and pinpoint which nerves, if any, are affected, your doctor will ask about your medical history and perform a thorough physical exam, paying special attention to your spine and legs.
You're also likely to have some basic tests that check your muscle strength and reflexes. For example, you may be asked to walk on your toes or heels, rise from a squatting position and, while lying on your back, lift your legs one at a time straight in the air. Pain that results from sciatica will usually become worse during these activities.
If your pain lasts longer than four weeks or is very severe, or you have another serious condition such as cancer, you may have one or more imaging tests to help identity why the sciatic nerve is compressed and to rule out other causes for your symptoms.
These tests include:
- Spinal X-ray. Because ordinary X-rays can't detect herniated disk problems or nerve damage, they're not usually helpful for pinpointing the cause of sciatica. A spinal X-ray can show most cancers affecting the bony structures of the spine, narrowed disks and spondylolisthesis, however, and can help rule out other causes of nerve root impingement.
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Magnetic resonance imaging (MRI). This is probably the most sensitive test for assessing sciatic nerve pain. Instead of X-rays, MRI uses a powerful magnet and radio waves to produce cross-sectional images of your back. The test can detect damage to your disks and ligaments as well as the presence of tumors. MRI is noninvasive and has no harmful side effects.
During the test, you lie on a movable table inside the MRI machine, which is essentially a large magnet. If you have a hard time lying still for the required period of time or you're anxious about the enclosed space, you may be given a sedative. Some MRI units may be wider, shorter or open on all sides, which may be more comfortable for you, although the quality of images taken with these systems may vary.
- Computerized tomography (CT) scan. This test uses a narrow beam of radiation to produce detailed, cross-sectional images of your body. When CT is used to image the spine, you may have a contrast dye injected into your spinal canal before the X-rays are taken — a procedure called a CT myelogram. The dye then circulates around your spinal cord and spinal nerves, which appear white on the scan.
