About This Page
This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Inflammatory back pain begins before age 45, improves with exercise, and worsens with rest
- MRI detects early sacroiliitis before x-ray changes
- HLA-B27 supports diagnosis but is not diagnostic
- First-line treatment is exercise/physical therapy plus NSAIDs
- Persistent active disease despite NSAIDs: TNF inhibitor or IL-17 inhibitor
Overview
Ankylosing spondylitis is radiographic axial spondyloarthritis involving sacroiliac joints, spine, and entheses. Chronic inflammation causes syndesmophytes, reduced spinal mobility, kyphosis, and sometimes bamboo spine.
Epidemiology
Usually begins in late adolescence or early adulthood. HLA-B27, family history, uveitis, psoriasis, and inflammatory bowel disease increase suspicion.
Clinical Features
Symptoms
Chronic low back or buttock pain before age 45
Morning stiffness >30 minutes, improves with exercise, not rest
Night pain improving after getting up
Alternating buttock pain
Painful red photophobic eye suggesting anterior uveitis
Signs
Reduced lumbar flexion and abnormal Schober test
Reduced chest expansion
Achilles or plantar fascia enthesitis
Peripheral asymmetric lower-limb arthritis
Kyphosis in advanced disease
Investigations
First-line
Focused clinical assessmentPattern recognition, red flags, functional impact, and targeted examination
Basic labs when indicatedCBC, CMP, ESR/CRP, CK, urinalysis, or disease-specific testing depending on suspected condition
Initial imaging when indicatedPlain radiographs or MRI/ultrasound based on suspected structural, inflammatory, infectious, or neurologic disease
Second-line
Disease-specific confirmatory testingAutoantibodies, HLA-B27, synovial fluid, nerve conduction studies, DEXA, or cultures as appropriate
MRI/ultrasound/CTUsed for early inflammatory disease, occult fracture, tendon tear, infection, or surgical planning
Screening before immunosuppressionTB, hepatitis, vaccination review, and baseline labs when biologic or high-risk therapy is planned
Specialist
Specialist referralRheumatology, orthopedics, infectious disease, ophthalmology, neurology, or spine surgery depending on red flags and disease severity
1
Initial management
- Address red flags and emergencies first
- Use guideline-directed first-line therapy matched to disease severity
- Educate the patient and set functional goals
- Use analgesia and rehabilitation when appropriate
2
Escalation
- Escalate to specialist-directed therapy if severe, refractory, progressive, or organ-threatening disease
- Use imaging, procedures, immunosuppression, antibiotics, or surgery according to diagnosis
- Monitor response objectively and revise diagnosis if response is atypical
3
Prevention and follow-up
- Manage comorbidities and medication toxicity
- Vaccinate and screen when immunosuppression is used
- Prevent disability, falls, fracture, infection, and functional decline
Complications
- Functional impairment: Pain, weakness, stiffness, deformity, or disability depending on disease
- Diagnostic delay: Missed infection, fracture, inflammatory disease, neurologic compromise, or organ-threatening complication
- Medication toxicity: NSAID, steroid, antibiotic, anticoagulation, opioid, or immunosuppressive adverse effects
- Chronic disease burden: Reduced quality of life, work impairment, deconditioning, and mental health impact
USMLE Step 2 CK Exam Tips
- 1Young patient + inflammatory back pain improving with exercise = ankylosing spondylitis
- 2HLA-B27 is supportive, not diagnostic
- 3Earliest imaging for suspected axial disease with normal x-ray = MRI SI joints
- 4Bamboo spine is a late finding
- 5Methotrexate does not treat axial disease
- 6Acute anterior uveitis needs urgent ophthalmology
practicetest your knowledge on ankylosing spondylitisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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