Severe pain doesn’t necessarily mean you need a scan, and mild pain sometimes does. Here are the five things patients tell me that prompt me to request one.
Most patients who come to see me ask whether they need an MRI scan.
The natural assumption is that the worse the pain, the more likely a scan is needed. The spine does not really work that way. Some patients in terrible pain do not need one straight away. Others with fairly mild back pain, but certain specific symptoms, prompt me to request one immediately.
First, how the decision is actually made
It is never based on a single sentence. It rests on the whole history, the examination findings, how long the symptoms have been present, and one further question that matters more than people realise: would the scan findings change how we manage your symptoms?
If the answer is no, the scan is of limited use.
With that said, here are five things patients say that make me think a scan will help.
1. “The pain radiates from my back all the way down my leg”
That is sciatica, from a trapped nerve in the lumbar spine.
It often settles within a few weeks, so I do not always request a scan straight away. But if it has persisted, that indicates a trapped nerve, and therefore a potential target for treatment.
That treatment need not be invasive. Sometimes an injection helps considerably; sometimes a small operation does.
2. “My foot keeps slapping the floor when I walk”
Or the foot feels weak or heavy, the ankle feels weak, or it is difficult to curl the toes or bend them upwards.
This often accompanies sciatica, but it signals something more: the nerve itself is in trouble and beginning to sustain damage.
Even if these symptoms are recent, I would want an MRI to confirm the diagnosis and potentially decompress the nerve to save its function.
3. “I can’t feel things properly when I need the toilet”
This could be cauda equina syndrome, usually caused by a large disc herniation compressing the nerves supplying the bladder and bowel sphincters.
Patients describe not feeling themselves when they wipe, or numbness in the genital area. It is often accompanied by pain down one or both legs. Frequently they cannot feel the need to go to the toilet, and at the end stage there is full incontinence.
Any of these signs is an absolute medical emergency. It needs immediate assessment by a doctor, a scan, and potentially surgery. This is not something to raise at a routine appointment.
4. “I’m dropping things, my hands feel clumsy”
Or difficulty buttoning shirts or doing up blouses.
This is often a sign of cervical myelopathy, arising from dysfunction of the spinal cord, usually through compression. The cord is the central structure transmitting messages between the brain and the body.
Compressed in the neck, it can affect both the arms and the legs. Compressed lower down, it may affect only the legs, and patients often feel unsteady on their feet.
Where spinal cord compression is suspected, we need to confirm it on MRI, because early decompression gives the best chance of recovering or at least preserving function.
5. “I’ve tried everything, the pain is getting worse, and it’s been months”
Pain localised to the lower back without referred leg pain rarely needs an MRI.
But where it has persisted, a scan can rule out anything sinister, a fracture for instance.
Here I must repeat a point I make often: people without back pain who undergo MRI scans show much the same wear-and-tear findings as people with it. We must be careful in how we interpret them.
That said, there are findings that offer clues. If a single disc is worn, common in itself, you can sometimes see inflammatory change in the bone above and below it, known as Modic changes. Still grounds for caution on their own. But if a SPECT CT scan then shows corresponding changes in the same region, that gives us a considerably higher level of confidence that this is the source of your pain.
That does not automatically mean the segment needs surgery. But where all other treatments have failed, fusing it can give good results.
The key takeaway
The intensity of your pain, particularly if it is acute or recent, is not on its own what determines whether you need a scan.
What I am predominantly looking for is:
- Signs of nerve entrapment
- Loss of function
- Urgent problems such as cauda equina syndrome or spinal cord compression
- How long the pain has gone on, and whether everything else has failed
