Do I need an MRI for sciatica?

Why an early scan is not always helpful

Sciatica and lumbar radicular pain are primarily assessed from the history and examination. The distribution of pain, altered sensation or weakness can suggest which nerve root is involved and whether another diagnosis needs consideration.

MRI is sensitive to age-related spinal change. Disc bulges, disc degeneration and narrowing can be present in people who have no pain. A report therefore cannot determine by itself whether a visible abnormality is responsible for a person’s symptoms.

For this reason, NICE advises that imaging should not routinely be offered in a non-specialist setting for low-back pain with or without sciatica. Even after referral for specialist opinion, a scan may not be necessary.

When MRI may be useful

In specialist care, MRI may be considered when its result is likely to change management. Examples include:

• persistent or severe symptoms where a targeted treatment or surgical opinion is being considered;
• pain, numbness or weakness that needs to be correlated with the level and side of a possible nerve-root problem;
• progressive or clinically important neurological findings;
• an atypical course or features that raise concern about a different underlying condition;
• planning an image-guided nerve-root or epidural procedure.

The decision is individual. Duration alone does not determine whether a scan is required, and an MRI should not delay urgent assessment when neurological emergency symptoms are present.

What can a lower-back MRI show?

An MRI gives detailed pictures of the discs, the central passage through the spine and the spaces where nerves leave it. It may show a slipped disc touching a nerve, narrowing around a nerve, narrowing of the main spinal canal—called spinal stenosis—or a less common problem.

The important question is whether the position of the scan finding makes sense for the person’s symptoms and examination. The most noticeable abnormality on a scan is not always the one causing pain.

What happens after the scan?

A scan is a decision-support tool rather than a treatment. Depending on the findings and clinical course, the next step may still be information, activity and rehabilitation; a review of medication; consideration of an image-guided injection; or referral for a spinal surgical opinion.

When symptoms and imaging do not correspond, it may be safer to reconsider the diagnosis than to pursue a procedure simply because the report describes an abnormality.

When might specialist assessment help?

Specialist assessment may be useful when it is unclear whether MRI would alter treatment, when an existing scan needs to be interpreted alongside symptoms and neurological findings, or when an injection or surgical opinion is being considered.

Dr Seyfried assesses patients with sciatica and lumbar radicular pain in London. Read about Dr Oliver Seyfried’s clinical practice and credentials or return to the main evidence-based guide to sciatica and lumbar radicular pain.