Axial spondyloarthritis and ankylosing spondylitis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Axial spondyloarthritis includes non-radiographic disease and radiographic axial spondyloarthritis historically called ankylosing spondylitis. The distinction reflects imaging, not symptom legitimacy. Diagnosis integrates onset, inflammatory features, associated disease, examination, HLA-B27, inflammatory markers and imaging. Women and HLA-B27-negative patients can be under-recognised, and normal mobility early in disease is not exclusionary.

Examine posture, spinal movement, chest expansion, sacroiliac provocation, hips, peripheral joints and entheses, while inspecting skin and nails and asking about eye and bowel symptoms. Mobility measures are useful longitudinally but influenced by age, effort, hip disease and damage. A painful red photophobic eye is not managed by routine rheumatology review; it needs same-day ophthalmic assessment.

NICE imaging starts with sacroiliac radiography in skeletally mature people on the relevant adult pathway. If definite sacroiliitis is absent but suspicion persists, request unenhanced MRI using an inflammatory-back-pain protocol and ASAS or OMERACT interpretation. If imaging and clinical suspicion disagree, seek specialist musculoskeletal-radiology review; consider follow-up MRI when suspicion remains high.

Management combines education, smoking cessation, regular exercise and physiotherapy with reviewed NSAID therapy. For ongoing active inflammatory disease, reassess diagnosis and mimics before applying current NICE targeted-treatment eligibility and sequencing. Recurrent uveitis favours a monoclonal TNF inhibitor, while active IBD rules against starting an IL-17 inhibitor; coordinate class choice with ophthalmology, gastroenterology or dermatology. Avoid forceful spinal manipulation in advanced ankylosis.

Key points

Consider axial spondyloarthritis when chronic back pain begins before age forty-five, especially with night waking, buttock pain and improvement with movement rather than rest.
Ask about uveitis, psoriasis, inflammatory bowel disease, enthesitis, dactylitis, peripheral arthritis and first-degree family history.
Normal CRP, negative HLA-B27 and normal radiographs do not exclude axial spondyloarthritis.
Follow the NICE imaging sequence: sacroiliac radiography when appropriate, followed by a protocolled MRI if suspicion remains and radiographs are nondiagnostic.
Structured exercise and physiotherapy addressing spinal mobility, posture, strength, aerobic fitness and breathing are central long-term treatments.
An NSAID trial may improve pain and stiffness when gastrointestinal, renal and cardiovascular risk permits; review effectiveness and toxicity rather than prescribing indefinitely by default.
For persistently active disease after appropriate non-pharmacological and conventional care, TNF, IL-17 or JAK inhibition may be selected under the applicable NICE approval; no class is generally superior for musculoskeletal efficacy. Choose jointly for licence and eligibility, prior response, comorbidity and extra-musculoskeletal disease. Prefer a monoclonal TNF inhibitor for recurrent or moderate-to-severe uveitis; in active inflammatory bowel disease prefer monoclonal TNF or JAK inhibition and do not start an IL-17 inhibitor.
Protect the ankylosed spine after trauma: maintain alignment, obtain urgent CT and add MRI after CT for a neurological abnormality potentially due to cord injury; image the rest of the spine when a new fracture is identified.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

HLA-associated susceptibility

HLA-B27 and other immune variants strongly influence susceptibility, but most carriers never develop disease and negative status does not exclude it.

Gut and barrier interaction

Microbial and mucosal immune signals may activate entheseal inflammation, supported by clinical overlap with inflammatory bowel disease and psoriasis.

Mechanical entheseal stress

Repeated loading at entheses interacts with immune susceptibility, helping explain inflammation at sacroiliac, spinal and peripheral insertion sites.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Enthesis-centred inflammation
Innate and adaptive immune pathways drive inflammation where ligaments and tendons attach to bone, including sacroiliac and spinal structures.
2
Erosion and repair
Inflammatory bone injury is followed by abnormal osteoproliferative repair, producing syndesmophytes, ankylosis and progressive restriction in some patients.
3
Systemic tissue involvement
Shared immune pathways affect uvea, bowel, skin and cardiovascular structures, so disease burden extends beyond measured spinal pain.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Inflammatory axial pattern

Young onset, insidious pain, second-half night waking, morning stiffness, alternating buttock pain and improvement with movement collectively support axial inflammation.

Extra-articular cluster

Uveitis, psoriasis, inflammatory bowel disease, enthesitis, dactylitis and family history substantially increase diagnostic probability and guide shared specialty care.

Radiographic structural disease

Sacroiliac erosions, sclerosis, joint-space change, syndesmophytes and ankylosis indicate established structural involvement but absence does not exclude earlier disease.

Acute uveitisRed flag

Unilateral eye pain, photophobia, redness and blurred vision requires same-day ophthalmic assessment to prevent sight-threatening complications.

Unstable spinal injuryRed flag

New severe focal pain, deformity or neurological change after minor trauma in an ankylosed spine requires emergency immobilisation, imaging and spinal review.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Sacroiliac-joint radiographyFirst step
Why
Identify definite structural sacroiliitis and alternative bony pathology in the NICE diagnostic sequence.
Interpretation and limitations
Normal or equivocal films do not exclude non-radiographic disease. Interpret structural or degenerative change in clinical context and continue the NICE MRI sequence when suspicion persists.
02
Inflammatory-back-pain protocol MRI
Why
Detect active and structural sacroiliac lesions when radiography is nondiagnostic and suspicion persists.
Interpretation and limitations
Use the specified protocol and ASAS or OMERACT interpretation. When imaging and phenotype disagree, seek specialist musculoskeletal-radiology review and consider follow-up MRI if suspicion remains high.
03
HLA-B27
Why
Modify diagnostic probability and referral decisions within a compatible clinical presentation.
Interpretation and limitations
A positive result is neither necessary nor sufficient; prevalence varies by ancestry and most carriers do not develop disease.
04
CRP and ESR
Why
Support activity assessment and provide a baseline for treatment monitoring.
Interpretation and limitations
Normal markers are common and cannot exclude active axial disease; unexplained elevation should prompt infection and other alternatives.
05
Spinal mobility, chest expansion and disease activity measures
Why
Quantify function and symptoms longitudinally for treatment and rehabilitation decisions.
Interpretation and limitations
Scores depend on damage, effort and comorbidity; combine them with examination, imaging and patient goals.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Mechanical back pain

Load-related pain improving with rest, focal strain and absent inflammatory or extra-articular features favours mechanical disease, although mechanisms can coexist.

Degenerative or infectious sacroiliitis

Age-related change, postpartum stress, osteitis condensans and infection can mimic sacroiliac abnormalities and require clinical and imaging correlation.

Diffuse idiopathic skeletal hyperostosis

Flowing anterolateral ossification in an older metabolic phenotype differs from inflammatory corner lesions and sacroiliac erosive disease.

Malignancy or fracture

Unremitting pain, systemic decline, trauma, neurological change or structural instability requires urgent alternative spinal assessment rather than an inflammatory label.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Suspected axial SpAUse clinical features and staged imagingFirst stepChronic back pain begins before forty-five with inflammatory or extra-articular features.

1Document onset, night symptoms, movement response, buttock pain, family history and psoriasis, uveitis, bowel, entheseal and peripheral-joint features.
2Refer according to NICE criteria, obtain HLA-B27 and markers when useful, and follow sacroiliac radiography then protocolled MRI when needed.
3Retain specialist follow-up or reassessment when early imaging is negative but the phenotype remains convincing rather than converting the diagnosis to mechanical pain automatically.

02Active established diseaseBuild from exercise to targeted therapyPain, stiffness and function remain impaired after diagnosis without an acute complication.

1Provide specialist physiotherapy and a sustainable home programme addressing mobility, posture, strength, aerobic fitness and chest expansion.
2Use an NSAID at the maximum tolerated dose for two to four weeks when safe; if pain relief remains inadequate, consider switching to another NSAID and reassess toxicity and diagnosis.
3Verify the diagnosis and inflammatory activity, then apply the NICE approval for the selected TNF, IL-17 or JAK inhibitor. Make a shared class choice from prior response, prognostic factors, comorbidity and extra-musculoskeletal disease rather than assuming universal TNF-first sequencing. Prefer a monoclonal TNF inhibitor for recurrent or moderate-to-severe uveitis; in active IBD prefer monoclonal TNF or JAK inhibition and do not start an IL-17 inhibitor, coordinating with the relevant specialty.

03Trauma or neurologyAssume instability until excludedAn ankylosed or markedly rigid spine develops new focal pain or neurological symptoms after trauma.

1Protect alignment, perform repeated neurological examination and involve emergency spinal services immediately, recognising that plain radiographs may miss fractures.
2Obtain urgent CT in the adult spinal-injury pathway. Add MRI after CT whenever a neurological abnormality may reflect cord injury, regardless of the CT result; if a new fracture is found, image the rest of the spinal column.
3DefinitiveMaintain specialist precautions and monitor for delayed displacement, epidural haematoma and respiratory compromise during transfer and definitive care.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

Reviewed NSAID trial for axial pain and stiffness alongside exercise when individual gastrointestinal, renal and cardiovascular risk is acceptable.

Naproxen

Common adult anti-inflammatory dosing is 250–500 mg orally twice daily with food, using the lowest effective dose for the shortest necessary period.

Assess ulcer or bleeding, renal, heart-failure, blood-pressure, cardiovascular, anticoagulant and interaction risks and add gastroprotection when indicated. Avoid systemic NSAIDs from 20 weeks of pregnancy unless essential; use the lowest dose for the shortest time and consider fetal monitoring after several days. They are contraindicated after 28 weeks.

TNF inhibitor for persistently active axial disease meeting NICE and specialist criteria after adequate non-pharmacological and NSAID management.

Adalimumab

The usual adult regimen for axial spondyloarthritis is 40 mg subcutaneously every other week under specialist prescribing and product information.

Do not start during active serious infection and stop for a new serious infection; screen for tuberculosis and hepatitis and update immunisation first. Avoid live vaccines during treatment, and seek an alternative in demyelinating disease. Adalimumab is contraindicated in NYHA III or IV heart failure. If continued through pregnancy, document exposure and the BSR plan to defer infant live vaccines until 6 months.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Spinal ankylosis and fracture

Rigid osteoporotic spine behaves like a long bone, allowing unstable fractures and delayed neurological injury after seemingly minor trauma.

Anterior uveitis

Acute unilateral painful red eye, photophobia and blurred vision can recur and threatens sight without prompt ophthalmic treatment.

Cardiopulmonary and bone disease

Restrictive chest movement, aortic-root disease, conduction abnormalities, osteoporosis and cardiovascular risk contribute to substantial long-term morbidity.

Work and functional loss

Pain, fatigue, stiffness and reduced spinal or hip movement can impair sleep, driving, work, exercise and mental wellbeing.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track validated activity and function measures together with spinal mobility, work and patient goals.
Review NSAID blood pressure, renal function, gastrointestinal and cardiovascular risk after initiation and periodically.
Ask directly about eye pain, psoriasis, bowel symptoms, chest restriction and new neurological features.
Before and during biologic therapy monitor infection, required bloods, vaccination and agent-specific adverse effects.
Assess fracture and osteoporosis risk, especially with advanced ankylosis, height loss, falls or long-term inflammation.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Radiographic status is not severity

Non-radiographic disease can be highly symptomatic and active; the term describes imaging rather than the reality of inflammation.

HLA-B27 modifies probability

Its value depends on ethnicity and phenotype, and it must never be used as a universal screening or exclusion test.

Exercise is disease care

Regular tailored mobility, posture, strength and aerobic work preserves function and complements rather than follows pharmacological treatment.

MRI needs context

MRI requires a protocol, recognised interpretation criteria and clinical context; specialist radiology review helps resolve discordance and prevents both overdiagnosis and missed disease.

The rigid spine is fragile

Long lever arms and poor bone quality produce unstable fractures after low-energy trauma, sometimes with delayed neurological deterioration.

11Common pitfallsFrequent interpretation and management errors.

01
Excluding disease because HLA-B27, CRP or radiography is negative.
02
Calling all young back pain inflammatory without associated features and examination.
03
Using MRI marrow oedema without considering mechanical and postpartum mimics.
04
Neglecting same-day referral for a painful photophobic red eye.
05
Treating spinal trauma as minor because initial radiographs appear normal.