Harvey's Garden

Reactive arthritis

Properties2
tags—
aliasesReA

4 min read

Etiology

  • Peak incidence: Age 20–40 years; M > F (up to 9:1 following GU infections; ~1:1 post-enteric).
  • Strong association with HLA-B27 (present in 30–50% overall, >80% with severe/axial disease).
  • Triggered 1–4 weeks following mucosal infection: c
    • Genitourinary (GU): Chlamydia trachomatis (most common overall).
    • Gastrointestinal (GI): Campylobacter jejuni, Salmonella enterica, Shigella flexneri, Yersinia enterocolitica, Clostridioides difficile.

Pathophysiology

Clinical features

Tip

The clinical manifestations are caused by immune complexes involving bacterial antigens. However, it does not represent disseminated infection, and joint aspirates are sterile (ie, it is a ‘reactive’ not infectious arthritis).

  • Classic Triad (present in full in <1/3 of patients): “Can’t see, can’t pee, can’t climb a tree” (Conjunctivitis, Urethritis, Arthritis).
    • Musculoskeletal Manifestations:
      • Asymmetric oligoarthritis (predominantly lower extremities: knees, ankles, MTPs).
      • Enthesitis: Inflammation at tendon insertion sites (e.g., Achilles tendonitis, plantar fasciitis).
      • Dactylitis: Diffuse soft-tissue swelling of entire digit (“sausage digit”).
      • Axial involvement: Inflammatory low back pain, buttock pain (sacroiliitis).
    • Extra-articular Manifestations:
      • Ocular: Sterile conjunctivitis (early, bilateral), anterior uveitis (photophobia, pain, red eye).
      • Genitourinary: Sterile urethritis, cervicitis, prostatitis, circinate balanitis.
      • Mucocutaneous:
        • Keratoderma blennorrhagicum: Hyperkeratotic, pustular/papular scaling lesions on palms and soles.
        • Circinate balanitis: Painless, superficial, serpiginous ulcerations on glans penis/corona. c
        • Painless shallow oral ulcers / stomatitis.
      • Systemic: Low-grade fever, fatigue, malaise, weight loss.

Mnemonic

Classic triad of reactive arthritis (seen in approximately one-third of affected individuals): “can’t see (conjunctivitis), can’t pee (urethritis), can’t climb a tree (arthritis)”.

Differential Diagnostics

BRANCH 1: ACUTE (< 6 weeks)

  • 1a: Acute Monoarthritis (1 Joint)
    • RED FLAG: Suspect Septic Arthritis? (Fever, chills, severe pain, erythema, warmth, ↓ROM)
      • YES -> URGENT ACTION: Hospitalize, Ortho/Rheum consult, Arthrocentesis STAT (Cell count & diff, Gram stain, Culture, Crystals), Blood cultures, CBC, ESR/CRP. Start empiric IV antibiotics AFTER aspiration.
    • Suspect Crystal Arthropathy (Gout/Pseudogout)? (Sudden onset, severe pain, prior episodes, triggers)
      • YES -> Arthrocentesis (Look for MSU/CPPD crystals), Serum Uric Acid (can be normal acutely), CBC, ESR/CRP, X-ray (may show chondrocalcinosis in pseudogout).
    • Suspect Trauma/Hemarthrosis? (History of injury, rapid swelling)
      • YES -> X-ray (rule out fracture), Consider Arthrocentesis (bloody fluid), CBC (if bleeding disorder suspected).
    • Other Possibilities: Early presentation of oligo/polyarthritis, Lyme disease (rarely mono).
  • 1b: Acute Oligo/Polyarthritis (≥2 Joints)
    • Inflammatory Features Present?
      • YES -> Consider:
        • Viral Arthritis: (e.g., Parvovirus B19, Hepatitis B/C, Rubella, HIV) - often symmetric, may have rash/flu-like prodrome. Workup: Viral serologies, LFTs, HIV test, CBC, ESR/CRP.
        • Reactive Arthritis: (Post-GI/GU infection, often asymmetric oligoarthritis, +/- urethritis, conjunctivitis, enthesitis) - Workup: Stool/Urine culture (if indicated), Chlamydia testing, HLA-B27, ESR/CRP.
        • Early Systemic Rheumatic Disease: (RA, SLE, PsA, SpA) - Workup: ESR/CRP, RF, Anti-CCP, ANA, Uric Acid, HLA-B27 (if SpA suspected), X-rays.
        • Serum Sickness: (Drug reaction) - History, rash, fever.
        • Lyme Disease: (Tick exposure history) - Lyme serology (may be negative early), ESR/CRP.
        • Acute Rheumatic Fever: (Post-strep infection, migratory polyarthritis - rare in developed nations) - ASO titre, Throat culture, ECG.
    • Non-inflammatory Features Dominant?
      • YES -> Consider: Uncommon acutely unless widespread OA flare or multiple joints injured. Workup: X-rays, ESR/CRP (usually normal).

BRANCH 2: CHRONIC (> 6 weeks)

  • 2a: Chronic Monoarthritis (1 Joint)
    • Inflammatory Features Present?
      • YES -> Consider:
        • Chronic Infection: (TB, Fungal, Lyme) - Workup: Arthrocentesis (AFB/fungal stain/culture, Lyme PCR), PPD/IGRA, Chest X-ray, ESR/CRP, Synovial biopsy may be needed.
        • Chronic Crystal Arthropathy: (Gout/Pseudogout) - Workup: Arthrocentesis (crystals), Uric Acid, X-ray.
        • Spondyloarthritis (SpA): (Esp. knee/hip) - Workup: HLA-B27, ESR/CRP, Imaging (X-ray, MRI of SI joints if back pain).
        • Pauciarticular JIA: (In younger patients).
    • Non-inflammatory Features Dominant?
      • YES -> Consider:
        • Osteoarthritis (OA): (Commonest cause) - Workup: X-ray (joint space narrowing, osteophytes), ESR/CRP (usually normal).
        • Avascular Necrosis (AVN): (Esp. hip, knee, shoulder; risk factors: steroids, alcohol) - Workup: X-ray (may be normal early), MRI is diagnostic.
  • 2b: Chronic Oligo/Polyarthritis (≥2 Joints)
    • Inflammatory Features Present?
      • YES -> Consider Systemic Rheumatic Diseases:
        • Rheumatoid Arthritis (RA): (Symmetric small joints, hands/feet, morning stiffness >1hr, nodules) - Workup: ESR/CRP, RF, Anti-CCP (specific), X-rays (erosions), +/- Ultrasound/MRI.
        • Spondyloarthropathies (SpA): (Incl. Ankylosing Spondylitis, Psoriatic Arthritis, Reactive, Enteropathic) - Often asymmetric, axial involvement (back pain), enthesitis, dactylitis, +/- skin/eye/GI symptoms. Workup: ESR/CRP, HLA-B27, X-rays (SI joints, spine), Skin/Nail exam, +/- MRI.
        • Connective Tissue Diseases: (SLE, Scleroderma, Polymyositis) - Look for specific extra-articular features (rash, Raynaud’s, photosensitivity, organ involvement). Workup: ESR/CRP, ANA, ENA panel, C3/C4, CK, Urinalysis.
        • Chronic Crystal Arthropathy: (Tophaceous Gout, CPPD) - Workup: Arthrocentesis, Uric Acid, X-rays.
        • Vasculitis: (Less common cause of arthritis) - Look for systemic signs (purpura, neuropathy, organ dysfunction). Workup: ANCA, ESR/CRP, Urinalysis, Biopsy (if indicated).
    • Non-inflammatory Features Dominant?
      • YES -> Consider:
        • Generalized Osteoarthritis (OA): (Hands - DIP/PIP/CMC1, Knees, Hips, Spine) - Workup: X-rays, ESR/CRP (normal).
        • Fibromyalgia: (Widespread pain, fatigue, sleep disturbance, tender points - not true joint inflammation) - Diagnosis of exclusion, often normal labs/imaging. Consider TSH, Vitamin D.

Treatment

Prognosis

  • Resolves spontaneously within a year
  • High rate of recurrence

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