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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
- Sterile arthritis after GU or GI infection
- Asymmetric lower-limb oligoarthritis with enthesitis is typical
- Triggers include Chlamydia, Salmonella, Shigella, Campylobacter, and Yersinia
- HLA-B27 predicts more severe/chronic disease
- NSAIDs are first-line; treat active infection
Overview
Reactive arthritis is a postinfectious seronegative spondyloarthritis. The joint is sterile, and symptoms usually begin 1-4 weeks after genitourinary or gastrointestinal infection.
Epidemiology
Most often affects young adults. Post-chlamydial disease is common in sexually active adults; enteric disease follows bacterial gastroenteritis.
Clinical Features
Symptoms
Asymmetric knee/ankle/foot arthritis after infection
Heel pain from Achilles enthesitis or plantar fasciitis
Urethritis, dysuria, or cervicitis
Recent diarrhea or abdominal pain
Conjunctivitis or painful photophobic uveitis
Signs
Warm swollen lower-limb joints
Dactylitis
Achilles or plantar fascia tenderness
Conjunctivitis or uveitis
Keratoderma blennorrhagicum or circinate balanitis
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
- 1Asymmetric oligoarthritis after urethritis or diarrhea = reactive arthritis
- 2Classic triad: arthritis, urethritis, conjunctivitis
- 3Chlamydia is classic GU trigger
- 4Synovial fluid is sterile inflammatory
- 5NSAIDs are first-line
- 6Treat active Chlamydia and partners
practicetest your knowledge on reactive arthritisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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