Learning Objectives
Differentiate between the four primary Seronegative Spondyloarthropathies (PAIR) using their unique clinical markers. Identify the strong association with HLA-B27 and recognize high-yield radiographic findings like the “Pencil-in-cup” deformity and “Bamboo spine.”
1. Common Features (The PAIR Complex)
These disorders are “seronegative” because they lack Rheumatoid Factor (IgM anti-IgG). They share a strong genetic link to HLA-B27 (MHC class I) and present with overlapping clinical features.
- Inflammatory Back Pain: Associated with morning stiffness that improves with exercise (unlike Osteoarthritis).
- Enthesitis: Inflammation where tendons/ligaments insert into bone (e.g., Achilles tendon).
- Dactylitis: Diffuse swelling of a finger or toe, known as “sausage fingers.”
- Uveitis: Anterior chamber inflammation (can lead to vision loss).
Subtypes of Spondyloarthritis
| Subtype | Key Clinical Findings | Classic Radiography |
|---|---|---|
| Psoriatic Arthritis | Asymmetric/patchy involvement. Associated with skin psoriasis and nail pitting. | “Pencil-in-cup” deformity (DIP joints). |
| Ankylosing Spondylitis | Symmetric sacroiliitis and spine fusion. Risk of aortic regurgitation and restrictive lung disease. | “Bamboo spine” (vertebral fusion). |
| IBD-Associated | Spondyloarthritis is seen in patients with Crohn’s disease or Ulcerative Colitis. | Sacroiliitis on imaging. |
| Reactive Arthritis | Post-infectious (GI or Chlamydia). Triad: Conjunctivitis, Urethritis, Arthritis. | Keratoderma blennorrhagica (palms/soles). |
2. Reactive Arthritis Triggers
This condition follows an infection (usually within 1–4 weeks). It is an autoimmune reaction, not an active infection of the joint itself.
- GI Pathogens: Shigella, Campylobacter, Salmonella, and Yersinia.
- Urogenital Pathogen: Chlamydia trachomatis.
Activity: Spondyloarthritis Diagnostic Quiz
High-Yield Mnemonics:
- The PAIR: Psoriatic, Ankylosing spondylitis, IBD, Reactive arthritis.
- Reactive Triad: “Can’t see (conjunctivitis), can’t pee (urethritis), can’t bend my knee (arthritis).”
- Reactive Bugs: “She Caught Students Cheating Yesterday” (Shigella, Chlamydia, Salmonella, Campylobacter, Yersinia).