Rheumatology

Ankylosing Spondylitis

Chronic inflammatory arthritis primarily affecting the sacroiliac joints and spine; strong HLA-B27 association leading to bamboo-spine ankylosis.

Last reviewed 12 Jul 2026 - MedicoMedics editorial team

Pathophysiology

IL-17/IL-23 axis-driven enthesitis with new bone formation; >90% HLA-B27 positive in Caucasians.

Sources: ACR AS 2019 (Arthritis Care Res 2019;71:1285); ASAS/EULAR 2022

Presentation

Inflammatory back pain (age <45, morning stiffness >30 min, improves with exercise), alternating buttock pain, enthesitis, uveitis, aortic regurgitation.

Diagnosis

ASAS criteria: back pain >=3 months plus sacroiliitis on imaging (X-ray or MRI) and HLA-B27 or clinical features. Elevated CRP supports.

Management

NSAIDs first-line; TNF inhibitors (adalimumab, etanercept) or IL-17 inhibitors (secukinumab, ixekizumab) for inadequate response. Physiotherapy essential; JAK inhibitors alternative.

Sample USMLE-style MCQs

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Question 1

A 26-year-old man has 6 months of morning back stiffness improving with exercise. HLA-B27 positive, MRI shows sacroiliitis. Diagnosis?

Question 2

Best initial pharmacotherapy?

Question 3

Which extra-articular feature is most common?

Question 4

Radiographic hallmark?

Question 5

If NSAIDs fail, best next agent?

References

Primary guidelines and peer-reviewed sources used for this entry. Reviewed 12 Jul 2026 by MedicoMedics editorial team.

Frequently asked

Classic X-ray finding?

Bilateral sacroiliitis, syndesmophytes, bamboo spine.

Extra-articular manifestation?

Acute anterior uveitis (up to 40%).

Which biologic class works?

TNF and IL-17 inhibitors both effective.

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