In short
Inflammatory back pain improves with movement, worsens with rest, wakes you in the second half of the night and usually starts before the age of 45. Mechanical back pain does the opposite. If your pain fits the first pattern and has lasted over three months, ask for a rheumatology assessment.
Back pain that improves when you move and worsens when you rest is the reverse of what most people expect. It is also the single most useful clue that the cause is inflammatory back pain rather than a pulled muscle or a worn disc.
The two behave in opposite directions. Mechanical back pain settles with rest and flares after a day on your feet, a long drive or an awkward lift. Inflammation settles with activity and punishes stillness, which is why the worst hours are the early morning and the ones spent sitting through a meeting.
The distinction matters. The treatments are different, and inflammation in the spine that goes unrecognised for years can stiffen and eventually fuse joints that will not come apart again. NICE states plainly that axial presentations of spondyloarthritis are often misdiagnosed as mechanical low back pain, leading to delays in access to effective treatments.
What inflammatory back pain means
The term describes pain coming from inflammation in the joints of the spine and, most often, in the sacroiliac joints, where the base of the spine meets the pelvis. It is not the same as pain from a disc, a facet joint or a muscle spasm, even though it can be felt in the same places.
The umbrella diagnosis is axial spondyloarthritis. It has two forms. In ankylosing spondylitis, changes at the sacroiliac joints or the spine can be seen on an X-ray. In the other form, the NHS explains that changes cannot be seen on an X-ray but can sometimes be seen on an MRI scan, and the symptoms and treatment are similar.
That second form is the reason so many people are told for years that their scans are normal. A normal X-ray rules out visible damage. It does not rule out active inflammation. You can read more on both under back pain and spondyloarthritis.
Waking in the second half of the night
This is the detail patients rarely volunteer and doctors rarely ask about, and it is one of the most discriminating features there is.
Inflammatory back pain typically wakes you between two and five in the morning. People describe getting up to walk around the room, standing under a hot shower, or sleeping the last part of the night in a chair because lying flat has become unbearable. Having walked about for ten or fifteen minutes, they can often go back to sleep.
Mechanical pain disturbs sleep in a different way. It hurts when you turn over or when you first shift position, then settles once you are still again. Turning is the trigger, not stillness.
Morning is the other reliable marker. Stiffness in the lower back that takes more than half an hour to loosen, day after day, fits inflammation. Fifteen minutes of creakiness on getting out of bed does not.
Age at onset, and why 45 is a line on the referral form
The NHS notes that ankylosing spondylitis usually first starts to develop between 18 and 40 years of age, and that symptoms build slowly over months or years rather than arriving overnight.
NICE uses two age thresholds. Chronic low back pain that began before the age of 45 is the entry point for a spondyloarthritis assessment, and onset before 35 further raises the likelihood compared with onset between 35 and 44.
This is precisely where the diagnosis is lost. A 26-year-old with three years of low back pain is told it is posture, a soft mattress, too much time at a desk or too little core strength. Some of that may be true. None of it explains waking at four in the morning or an hour of stiffness at seven.
If the pain started in your twenties or thirties, has lasted longer than three months, and comes and goes rather than following any injury, age is working in favour of inflammatory back pain rather than against it.
Buttock pain that swaps sides
Inflamed sacroiliac joints often hurt deep in one buttock rather than in the middle of the back. Many people point to a spot beside the tailbone and describe a dull, boring ache rather than a sharp catch. NICE lists buttock pain among its referral criteria for exactly this reason.
The feature worth noticing is that it alternates. Left buttock for a few weeks, then the right, then back again. Nothing mechanical moves across the midline like that.
This pain is often mistaken for sciatica. Sciatica usually travels down the back of the leg past the knee and comes with tingling, numbness or weakness in a defined strip of skin. Sacroiliac pain tends to stop at the back of the thigh and carries no numbness.
Hip pain deserves the same care. Pain felt in the groin on walking is more likely to be the hip joint itself, whereas pain at the back of the pelvis that eases as you keep walking is not.
What mechanical back pain looks like
Most back pain is mechanical, and most of it gets better. The NHS describes back pain as very common and says it usually improves within a few weeks, with a pulled muscle among the commonest causes.
The mechanical pattern is recognisable. There is often a triggering event, such as lifting a gas cylinder or twisting while carrying a child. The pain is worse with a particular movement, better lying flat, and worst at the end of the day rather than at the start of it. Morning stiffness lasts a few minutes, not an hour.
Mechanical pain also tends not to bring anything else with it. No fatigue out of proportion, no eye trouble, no rashes, no gut symptoms, no family pattern.
A slipped disc, spinal stenosis and facet joint arthritis all belong in this group. They are real, they can be disabling, and they need proper treatment. They are simply a different problem from the one this article is about.
Clues outside the spine: eyes, skin, gut and heels
Spondyloarthritis is a whole-body condition that happens to involve the spine, so the strongest supporting evidence is often nowhere near the back. NICE points to enthesitis and dactylitis as musculoskeletal signs, and to uveitis and psoriasis, including psoriatic nail changes, as signs outside the joints. Recent genitourinary infection and a family history of spondyloarthritis or psoriasis count as risk factors.
Look for these in your own history:
- Pain at the back or under the heel, or where the ribs meet the breastbone
- A whole finger or toe that swelled up like a sausage, even briefly, even years ago
- A red, painful, light-sensitive eye that needed drops from an eye doctor
- Psoriasis anywhere, including only the scalp or a pitted nail
- Long-standing loose stools, blood in the stool or a diagnosis of Crohn's disease or ulcerative colitis
- A parent, brother or sister with spondylitis, psoriasis or inflammatory bowel disease
A painful red eye with blurred vision needs same-day assessment by an eye specialist, not a wait-and-see week. Bowel symptoms alongside back pain point towards arthritis linked to inflammatory bowel disease, and skin involvement towards psoriatic arthritis.
The referral criteria a GP is working from
NICE sets out a specific rule. If someone has low back pain that started before the age of 45 and has lasted more than three months, they should be referred to a rheumatologist when four or more additional criteria are present. The nine criteria include:
- Back pain that started before the age of 35
- Waking during the second half of the night because of symptoms
- Buttock pain
- Improvement with movement
- Improvement within 48 hours of taking an anti-inflammatory medicine
- A first-degree relative with spondyloarthritis, or current or past arthritis, enthesitis or psoriasis
If exactly three criteria are present, NICE advises testing for HLA-B27 and referring if the result is positive. It is worth taking this list to your appointment and going through it item by item, because it is the framework a doctor is expected to use when inflammatory back pain is suspected.
What X-rays, MRI and HLA-B27 can and cannot settle
NICE is unusually direct about the limits of testing here, warning that spondyloarthritis should not be ruled out on the basis of any single sign, symptom or test result.
Three specific warnings are worth memorising. Axial spondyloarthritis affects a similar number of women as men, which is why it is still missed in women who were told it is a young man's disease. It occurs in people who are HLA-B27 negative. And it may be present despite no evidence of sacroiliitis on a plain X-ray.
That is why an MRI of the sacroiliac joints is often the decisive test, since it can show active inflammation before any damage appears. The HLA-B27 test is a probability adjuster, not a verdict, and a great many healthy people carry the gene without ever developing anything. There is more in the article on what a positive HLA-B27 result actually means.
Blood markers such as CRP and ESR may be raised, but normal results are common and do not clear you.
Back pain that needs same-day help
Most back pain is not dangerous. A small number of presentations are, and they override everything above.
Call for emergency help if you develop numbness or tingling in both legs, loss of feeling around the genitals or back passage, difficulty passing urine or loss of control of the bladder or bowels. The NHS lists these as reasons to go to hospital immediately, because pressure on the nerves at the base of the spine has to be relieved quickly.
Seek urgent same-day advice if back pain comes with fever, shivering or feeling generally unwell, or if severe pain starts suddenly and is worsening quickly. Infection in the spine and, rarely, cancer can present this way.
Do not sit on unexplained weight loss, a new lump or change in the shape of the back, pain that is worse at night and not improved by rest, or pain high between the shoulder blades rather than in the lower back. These need a doctor within days.
Taking this pattern to a doctor
Go in with evidence rather than a description. Write down the year the pain started, how long the morning stiffness lasts, whether you wake in the second half of the night, and what happens on a day when you walk a lot compared with a day spent sitting. Note any eye, skin, gut or heel history, and any relative with similar problems.
Bring previous X-rays and MRI films themselves rather than only the reports, in date order, and a list of everything you take for pain. If anti-inflammatory tablets help within a day or two, say so, since that response is itself one of the criteria. Do not stop anything you have been prescribed in order to make the picture clearer, and speak to your rheumatologist before changing anything.
Treatment begins with a structured exercise and physiotherapy programme, which does more here than in almost any other spinal condition, because back pain that improves with exercise responds to being kept moving. Where inflammation persists despite that, targeted biologic and immunomodulatory treatment can control it and help delay progression. If you are unsure whether your pattern warrants a specialist opinion at all, the guide on when to see a rheumatologist sets out the thresholds.
Common questions
Can back pain be inflammatory if my X-ray is normal?
Yes. Inflammation of the sacroiliac joints can be active for years before any change shows on a plain X-ray, and some people never develop X-ray changes at all. An MRI of the sacroiliac joints is more sensitive early on. A normal X-ray should not close the question if the pattern fits.
I am a woman in my thirties with back pain. Is spondyloarthritis unlikely?
No. NICE specifically warns that axial spondyloarthritis affects a similar number of women as men, and the belief that it is a young man's condition is a common reason it is missed in women. The pattern of the pain matters far more than your sex.
How long should I wait before asking for a specialist opinion?
Three months of back pain is the usual threshold, provided it started before you were 45 and follows the inflammatory pattern. Waiting longer rarely adds information. If the pain wakes you at night and eases with movement, ask at three months rather than at three years.
Does a negative HLA-B27 test rule out inflammatory back pain?
No. NICE states that axial spondyloarthritis can occur in people who are HLA-B27 negative. The test shifts probability rather than deciding anything. Diagnosis rests on the pattern of symptoms, the examination, imaging and the presence of related features such as uveitis or psoriasis.
Sources
- NICE NG65 - Spondyloarthritis in over 16s: recommendations www.nice.org.uk
- NHS - Ankylosing spondylitis: symptoms www.nhs.uk
- NHS - Ankylosing spondylitis: overview www.nhs.uk
- NHS - Back pain www.nhs.uk
This article is general information and does not replace a consultation.