L180/ 100
Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas·2026·Systematic review
Ankylosing Spondylitis
An inflammatory arthritis that primarily affects the spine and sacroiliac joints — also called axial spondyloarthritis or AS
ICD-10: M45.9 · systemic condition
Ankylosing spondylitis (AS) — also known as axial spondyloarthritis — is a type of inflammatory arthritis that primarily targets the spine and the sacroiliac joints where the spine meets the pelvis. Unlike mechanical back pain (which is caused by disc degeneration or muscle strain), AS is driven by immune system inflammation. Over time, chronic inflammation can cause new bone formation, leading to the fusion of spinal segments — a process called ankylosis. Early diagnosis and treatment with biologic medications can slow progression and significantly improve quality of life.
Symptoms
- Chronic low back and buttock pain that is worse in the morning or after rest (inflammatory pattern)
- Morning stiffness lasting more than 30 minutes that improves with activity
- Back pain that wakes you from sleep in the second half of the night
- Reduced spinal flexibility and difficulty bending forward
- Fatigue, a common systemic feature of inflammatory disease
- Chest pain with deep breathing (rib cage involvement in some patients)
- Eye inflammation (uveitis) — affecting approximately 25–40% of patients
- Hip and shoulder pain in more severe cases
Causes & Risk Factors
- Genetic predisposition — approximately 90% of patients carry the HLA-B27 gene variant
- Immune system dysregulation triggering chronic spinal inflammation
- Gut microbiome alterations may play a contributing role (active research area)
- Environmental triggers in genetically susceptible individuals
- Note: AS is not caused by injury or mechanical stress, unlike most other back pain
Imaging Findings
Imaging studies are commonly used to identify findings associated with this condition. Results vary by individual; a qualified spine specialist interprets findings in the context of a full clinical evaluation.
MRI
- STIR or T2 fat-saturated sequences of the sacroiliac joints are the most sensitive tool for detecting active sacroiliitis: bone marrow oedema (bright signal) in the subchondral bone is the hallmark of active inflammation in axial spondyloarthritis
- Whole-spine MRI can identify spondylitis (Romanus lesions — vertebral corner inflammatory lesions), syndesmophyte formation, and the characteristic bamboo spine in advanced disease
- ASAS MRI criteria for positive sacroiliitis: 2 or more bone marrow oedema lesions on a single slice, or 1 or more lesions per slice on 2 or more consecutive slices; results vary by individual and require specialist interpretation
CT Scan
- CT is superior to plain films for detecting structural sacroiliitis: erosions, sclerosis, joint space narrowing, and partial or complete ankylosis are well-characterised
- CT provides detailed assessment of syndesmophytes, vertebral squaring, and thoracic cage deformity in advanced disease
- CT is preferred when MRI is contraindicated; lower sensitivity for early active inflammation compared to MRI with STIR sequences
X-Ray
- AP pelvis radiograph is used to grade sacroiliitis (New York criteria grade 0-4); bilateral grade 2 or unilateral grade 3 fulfils the modified New York criteria for radiographic axial SpA (ankylosing spondylitis)
- Lateral spine radiograph may show vertebral squaring, Romanus lesions (erosion of vertebral corners), syndesmophytes, and bamboo spine in established disease
- Radiographic changes lag behind clinical and MRI inflammation by years to decades; a normal X-ray does not exclude early axial spondyloarthritis
Who Is Commonly Affected
The following patterns are commonly associated with this condition based on published population studies. Individual presentation varies; these figures are informational only.
Peak Age Range
Inflammatory back pain most commonly begins between ages 17 and 35; diagnosis is often delayed 5-10 years after symptom onset due to the insidious onset and early normal X-rays
Gender Distribution
Men are affected approximately 2-3 times more often than women for radiographic AS; non-radiographic axial SpA has a roughly equal sex distribution
Estimated Prevalence
Global prevalence of ankylosing spondylitis estimated at 0.1-0.5% of the general population; HLA-B27 positivity is present in approximately 90% of cases in White European populations; prevalence varies widely by ethnicity and HLA-B27 prevalence in the population; based on published population studies, individual presentation varies
Treatment Options
Conservative
- NSAIDs (ibuprofen, naproxen, celecoxib) — first-line treatment for pain and stiffness; some may slow radiographic progression
- Physical therapy emphasizing spinal mobility, posture, and breathing exercises
- Regular aerobic exercise — swimming and water aerobics are particularly well-tolerated
- TNF inhibitors (biologics): adalimumab, etanercept, infliximab — highly effective when NSAIDs fail
- IL-17 inhibitors: secukinumab, ixekizumab — an alternative biologic class
- JAK inhibitors (tofacitinib, upadacitinib) — newer oral options for refractory disease
- Sulfasalazine — limited spinal benefit but may help peripheral joint involvement
Surgical
- Spinal osteotomy — corrective procedure for severe fixed kyphotic deformity (bent-forward posture) preventing patients from looking straight ahead
- Total hip replacement — for patients with severe hip joint involvement
- In general, AS is a medical condition managed with medications; surgery is reserved for deformity correction or failed joints
When to see a spine specialist
See a rheumatologist promptly if you have had chronic low back pain lasting more than 3 months that started before age 45, is worse in the morning, improves with exercise but not rest, and is associated with buttock pain alternating sides. Early diagnosis and biologic therapy can prevent irreversible spinal fusion. See a spine surgeon if you develop severe spinal deformity or neurological symptoms.
Specialists Who Treat Ankylosing Spondylitis
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Questions to Ask Your Doctor
Bring these questions to your next appointment about ankylosing spondylitis.
- 1
Has inflammatory back pain been formally distinguished from mechanical back pain in my case — and do I meet ASAS classification criteria for axial spondyloarthritis?
- 2
What is my HLA-B27 status, and how does that influence the diagnostic certainty and expected treatment response?
- 3
Have I had MRI of the sacroiliac joints to look for inflammatory changes (bone marrow oedema) — and if findings are present or absent, how does that affect my diagnosis and management plan?
- 4
Have NSAIDs been adequately trialled before moving to biologic (TNF or IL-17 inhibitor) therapy — and if biologics are being considered, which agent is preferred given my symptom profile and any extra-articular features?
- 5
What are the key extra-spinal features of ankylosing spondylitis I should be aware of — such as uveitis, psoriasis, or inflammatory bowel disease — and how would those be managed?
Clinical Evidence
Key Research
- L4Challenges in the diagnosis of axial spondyloarthritis (2023)
- L4MRI lesions of the spine in patients with axial spondyloarthritis — updated lesion definitions and ASAS validation (2022)
- L1Risk of new-onset and recurrent uveitis with different biologics for ankylosing spondylitis: a network meta-analysis (2025)
- L1Comparative efficacy, safety and immunogenicity of biosimilars vs. reference biologics in ankylosing spondylitis (2025)
Frequently Asked Questions
Is ankylosing spondylitis the same as inflammatory back pain?
Inflammatory back pain is a clinical pattern — morning stiffness, improvement with exercise, worse with rest — that suggests an inflammatory cause. Ankylosing spondylitis is one specific diagnosis within the axial spondyloarthritis spectrum that causes inflammatory back pain. Not all inflammatory back pain is AS, but AS always presents with an inflammatory pattern.
Does everyone with ankylosing spondylitis develop spinal fusion?
No — not all patients with AS develop significant bony fusion (ankylosis). The risk is highest in patients with elevated inflammation markers, significant sacroiliac joint involvement on imaging, and those who are inadequately treated. Early diagnosis and consistent treatment with NSAIDs and biologics substantially reduces the risk of structural progression.
What is the difference between ankylosing spondylitis and degenerative disc disease?
Degenerative disc disease is a wear-and-tear process that worsens with activity and improves with rest. Ankylosing spondylitis is an inflammatory disease that is worse in the morning and after rest, and improves with movement. Blood tests (CRP, ESR, HLA-B27) and MRI of the sacroiliac joints help differentiate the two.
Which specialist should I see for ankylosing spondylitis?
A rheumatologist is the primary specialist for diagnosing and managing AS with biologic medications. Spine surgeons (orthopedic or neurosurgeons) are consulted for severe deformity or neurological complications. Some patients also work with physiatrists or pain management specialists for additional symptom control.