Inflammatory back pain starts gradually before the age of 45, lasts more than three months, is worse with rest and better with movement, wakes you in the second half of the night, and responds strikingly well to anti-inflammatories. It is the warning sign of axial spondyloarthritis.
Estimates put the proportion of people consulting a GP with persistent low back pain who have an inflammatory cause at roughly one in twenty. The problem is not that the condition is rare. It is that the two feel similar enough to be mistaken for each other for years.
Why the difference matters so much
years, on average, between the first symptoms of axial spondyloarthritis and the diagnosis in the United Kingdom. The target set by the National Axial Spondyloarthritis Society is one year.
National Axial Spondyloarthritis Society, UK figure
That figure is the reason this article exists. Eight and a half years is not a diagnostic curiosity, it is a decade of a working life spent with untreated inflammation, and the National Axial Spondyloarthritis Society has set a gold standard of one year precisely because the gap is so wide.
The delay is not usually anybody’s fault in a single consultation. Back pain is the most common reason adults consult about a musculoskeletal problem in the UK, the overwhelming majority of it is mechanical, including the leg pain people call sciatica, and inflammatory cases hide inside that volume. Leg pain that traces a single nerve root’s territory is a different problem again, and it is not what this article describes. What closes the gap is the patient describing the pattern precisely, and the clinician recognising it.
Inflammatory or mechanical: the reversal test
Two kinds of back pain that behave in opposite ways
Mechanical back pain
- Comes on after a specific movement or a heavy day.
- Better with rest, worse with activity.
- Stiffness on waking lasts a few minutes.
- Nights are usually undisturbed.
- Anti-inflammatories help variably.
- Most episodes settle within six weeks.
Inflammatory back pain
- Comes on gradually, often with no trigger at all.
- Better with movement, worse with rest.
- Stiffness on waking lasts more than thirty minutes.
- Wakes you in the second half of the night.
- Anti-inflammatories often work strikingly well, within 48 hours.
- Persists beyond three months and keeps coming back.
Every feature in the right hand column is the opposite of what an ordinary strained back does. That is the most reliable way to hold on to the distinction. A mechanical back hurts because you did too much; an inflammatory back hurts because you did too little, and it punishes stillness. Stiffness that eases within ten or twenty minutes of moving and returns after the next spell of sitting is the ordinary behaviour of connective tissue that has stopped gliding, and it is not the hour or more that defines this condition.
The night pattern is the most specific single feature. Inflammatory back pain characteristically wakes people in the second half of the night, and, crucially, they have to get up and move before it settles. Turning over is not enough.
The response to anti-inflammatories is the other giveaway. In mechanical back pain they take the edge off. In inflammatory back pain the effect is often dramatic and fast, within a day or two, and that response is itself part of the diagnostic picture. Many people notice it years before anybody asks.
What is actually inflamed
Not the disc, and not the muscle. Inflammatory back pain in this sense comes from the entheses, the points where ligaments and tendons anchor into bone, and from the sacroiliac joints where the base of the spine meets the pelvis. The same entheses inflame elsewhere, which is why a painful tendon insertion at the elbow or the heel, in someone with this pattern of back pain, is worth mentioning rather than filing as an overuse tendinopathy.
The umbrella condition is axial spondyloarthritis. Ankylosing spondylitis is the form in which changes are visible on plain X-rays; non-radiographic axial spondyloarthritis is the same disease before those changes appear, and it causes just as much pain. The distinction is radiological, not a measure of how bad your symptoms are.
Inflammatory back pain is not exclusive to that group. It also occurs in psoriatic arthritis and in arthritis associated with inflammatory bowel disease, and this is why a GP asking about your skin, your eyes and your bowel habit is not changing the subject. Psoriasis, a painful red eye that recurs, and unexplained bowel symptoms all belong in the same conversation. So do pitted nails and a finger swollen along its whole length, which are the fingerprints of psoriatic arthritis.
The NICE referral rule, written out
| The two entry conditions | The seven additional criteria |
|---|---|
| Low back pain that started before the age of 45 and has lasted longer than 3 months Four or more of the criteria opposite trigger referral to a rheumatologist. With exactly three, an HLA-B27 test is done first and referral follows a positive result. |
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 | |
| A close relative with spondyloarthritis, or current or past psoriasis | |
| Inflammatory arthritis, enthesitis, or joint pain and swelling not caused by injury |
Two things about this rule are worth understanding. First, it is deliberately generous, because the cost of missing an inflammatory cause is far higher than the cost of a rheumatology appointment that turns out to be reassuring. Second, it exists in a national guideline that any GP can look up while you are in the room.
Note the age criteria. Onset before 45 is the entry condition, and onset before 35 counts again as an additional criterion, because the younger the start the more likely inflammation is. A back that first went wrong at 24 and has never been right since is a different story from a back that started aching at 58.
What the tests actually tell you
There is no blood test that says yes or no. Inflammatory markers such as CRP are raised in some people with active disease and entirely normal in others, so a normal result does not close the question. This is the point at which many people are wrongly reassured.
HLA-B27 is a genetic marker, not a diagnosis. It is carried by a meaningful slice of the healthy British population who will never develop anything, and it is absent in a minority of people who definitely have the disease. In the NICE pathway it is used as a tie breaker when exactly three additional criteria are present, which is exactly the right way to use it.
MRI of the sacroiliac joints is the investigation that shows active inflammation, and it can be positive years before a plain X-ray changes. If a normal X-ray has been used to rule the condition out for you, that reasoning is out of date.
None of this means the tests are useless. A raised CRP alongside the right history strengthens the case considerably, and a positive HLA-B27 in someone meeting three criteria is exactly what the NICE pathway is designed to act on. However, the order matters: the clinical pattern leads, and the tests follow it. Reversing that order is how people end up reassured by a normal blood result and sent away for another three years.
How it is treated
Exercise comes first and stays first. A structured programme built around spinal mobility, chest expansion, posture and general aerobic fitness is the backbone of treatment, and rheumatology physiotherapists in the NHS deliver it. The gains are lost quickly when the programme stops, which is why it is framed as a long term habit rather than a course.
Anti-inflammatory medicines are the first drug treatment, and in this condition they are used as regular treatment rather than as occasional pain relief. If two of them at full dose over several weeks do not control the disease, that failure is itself the trigger for the next step.
Biologic treatments, which block specific inflammatory signals, changed the outlook for this condition. They are prescribed by rheumatology and reserved for people whose disease remains active despite anti-inflammatories, and they are a large part of why an early diagnosis is worth so much more than a late one.
Alongside treatment, the general inflammatory load matters. Stopping smoking has a measurable effect on the course of axial spondyloarthritis, sleep and weight both influence how much pain people report, and the diet advice is the same unglamorous advice given for every chronic inflammatory condition. If you are adding a supplement to that, judge a bioavailable anti-inflammatory formula on absorption rather than on label doses, and treat anything aimed at persistent back pain as an addition to the exercise programme rather than a substitute for a rheumatology referral.
What to do while you wait
- Keep a two week diary. Time your morning stiffness from waking to normal movement, and note the nights you are woken and whether you had to get up.
- Count your criteria against the table above, and write down which ones you meet.
- List the family history. Spondyloarthritis, psoriasis and inflammatory bowel disease in parents, siblings or children all count.
- Note the response to anti-inflammatories if you have taken any, and how fast it came.
- Keep moving. Do not rest an inflammatory back. Walking, swimming and daily mobility work are treatment, not a risk.
Bring that single sheet to the appointment. It converts a vague complaint of chronic back pain into a structured case that fits a national referral rule, and it is the most effective thing a patient can do to shorten the delay.
Red flags that need urgent attention
- New weakness in a leg or foot, or a foot that drags.
- Numbness around the saddle area, or loss of bladder or bowel control. This is an emergency.
- Back pain with fever, night sweats or unexplained weight loss.
- A painful, red, light sensitive eye, which can be uveitis and needs same day assessment.
- Back pain following significant trauma, or in anyone with a history of cancer.
Frequently asked questions
What does inflammatory back pain feel like?
A deep ache low in the back and across the buttocks that builds over weeks rather than starting with an injury. It is stiff and heavy in the morning for more than half an hour, wakes you in the small hours, and eases once you get up and move. People often describe pacing the kitchen at four in the morning because lying still is worse than walking.
How do I know if my back pain is inflammatory or mechanical?
Use the reversal test. Mechanical pain is worse with activity and better with rest. Inflammatory pain is worse with rest and better with movement. Add three more questions: did it start before you were 45, has it lasted more than three months, and does the morning stiffness run past thirty minutes? Yes to all four makes inflammatory back pain likely enough to ask a GP about spondyloarthritis directly.
What causes inflammatory back pain?
Immune driven inflammation at the points where ligaments and tendons attach to bone, particularly at the sacroiliac joints where the spine meets the pelvis. The commonest cause is axial spondyloarthritis, which includes ankylosing spondylitis. It also appears with psoriatic arthritis and with inflammatory bowel disease, which is why a GP will ask about skin, eyes and bowels as well as the back.
Does a blood test diagnose inflammatory back pain?
No single test does. Inflammatory markers are raised in only some people with active disease, so a normal result proves nothing. HLA-B27 is a genetic marker that shifts the odds rather than settling the question: it is carried by a substantial minority of the healthy population and it is absent in a proportion of people who do have the condition. MRI of the sacroiliac joints is the most informative investigation.
Is exercise good for inflammatory back pain?
It is the cornerstone of treatment, not an optional extra. A structured exercise programme covering spinal mobility, posture and general fitness protects range of movement and reduces symptoms, and physiotherapists in rheumatology services build it around the individual. The instinct to rest a painful back works against you here, which is the opposite of the advice given for a mechanical strain.
How long does inflammatory back pain last?
It is a long term condition rather than an episode, but that does not mean constant pain. Most people have flares and quieter periods, and effective treatment can keep symptoms low for years at a time. What matters is starting treatment early, because the inflammation that goes untreated for a decade is the inflammation most likely to change the shape of the spine.
Should I see a GP or go straight to a specialist?
Start with the GP, because rheumatology referral in the NHS goes through primary care. Take the NICE criteria with you and say which ones apply to you. If you meet four of the seven additional criteria and the pain started before 45 and has lasted over three months, you fit the referral rule, and it is entirely reasonable to say so.
What to take away
Tomorrow morning, time it. From the moment you wake to the moment your back moves normally. If that number is over thirty minutes most days, and the pain started before you were 45, and it has been going for more than three months, you are describing inflammatory back pain and not a bad back.
Take the number, the criteria and the family history to a GP, and name the condition. The average British patient waits eight and a half years for someone to do that.
Sources
Hartvigsen J., Hancock M.J., Kongsted A. et al. (2018). What low back pain is and why we need to pay attention. The Lancet, 391(10137), 2356-2367. DOI: 10.1016/S0140-6736(18)30480-X
Foster N.E., Anema J.R., Cherkin D. et al. (2018). Prevention and treatment of low back pain: evidence, challenges, and promising directions. The Lancet, 391(10137), 2368-2383. DOI: 10.1016/S0140-6736(18)30489-6
Sieper J., Poddubnyy D. (2017). Axial spondyloarthritis. The Lancet, 390(10089), 73-84. DOI: 10.1016/S0140-6736(16)31591-4
GBD 2021 Low Back Pain Collaborators (2023). Global, regional, and national burden of low back pain, 1990-2020, its attributable risk factors, and projections to 2050. The Lancet Rheumatology, 5(6), e316-e329. DOI: 10.1016/S2665-9913(23)00098-X
Jensen R.K., Kongsted A., Kjaer P., Koes B. (2019). Diagnosis and treatment of sciatica. British Medical Journal, 367, l6273. DOI: 10.1136/bmj.l6273
Robinson W.H., Lepus C.M., Wang Q. et al. (2016). Low-grade inflammation as a key mediator of the pathogenesis of osteoarthritis. Nature Reviews Rheumatology, 12(10), 580-592. DOI: 10.1038/nrrheum.2016.136
