📚 Lecture Overview
This lecture covers Seronegative Spondyloarthropathies (SpA), a heterogeneous group of rheumatic diseases characterized by common clinical and genetic features without the presence of rheumatoid factor. The primary conditions discussed include Ankylosing Spondylitis (AS), Reiter's syndrome (Reactive Arthritis), and Psoriatic Arthritis (PsA). Mastering these disorders is crucial for diagnosing inflammatory back pain and peripheral arthropathies early to prevent irreversible joint damage and spinal fusion.
🎯 Key Concepts & Definitions
- Spondyloarthropathy (SpA): A group of interrelated rheumatic diseases classified as peripheral or axial based on affected body parts, strongly linked to HLA-B27.
- Enthesitis: Inflammation of the entheses, the sites where tendons, ligaments, or joint capsules attach to bone; a hallmark feature of SpA.
- Syndesmophytes: Vertical bony growths that bridge adjacent vertebrae, ultimately leading to a rigid "bamboo spine" in advanced Ankylosing Spondylitis.
- Dactylitis: Diffuse swelling of an entire digit ("sausage digit"), commonly seen in reactive arthritis and psoriatic arthritis.
- Pencil-in-cup deformity: A characteristic radiographic finding in psoriatic arthritis caused by severe bone destruction and resorption at digital joints.
📖 Main Content
1. Ankylosing Spondylitis (AS)
Ankylosing Spondylitis is a chronic inflammatory disease primarily affecting the axial skeleton.
- Patient History & Presentation:
- Insidious onset of low back pain before age 40 lasting > 3 months.
- Symptoms are worse in the morning or with inactivity and improve with exercise.
- Skeletal & Extra-articular Manifestations:
- Spinal involvement leads to flattening of the lumbar curve, exaggeration of thoracic curvature, and limited chest expansion.
- Uveitis occurs in up to 25% of patients.
- Cardiovascular complications include aortitis, aortic valve incompetence, and conduction abnormalities.
- Apical fibrobullous disease in the upper lung fields can mimic tuberculosis.
- Laboratory & Imaging:
- HLA-B27 is present in 90-95% of patients.
- X-ray reveals bilateral symmetrical sacroiliitis and bamboo spine due to syndesmophyte formation.
- MRI detects early bone marrow edema and inflammation.
- Diagnostic & Treatment Approach:
- Diagnosed using the 1984 New York criteria (clinical back pain criteria + radiological sacroiliitis).
- First-line medical therapy: Full anti-inflammatory doses of NSAIDs.
- Anti-TNF agents (e.g., adalimumab, infliximab) or IL-17 inhibitors (secukinumab) are used for patients unresponsive to NSAIDs.
2. Reactive Arthritis (Reiter's Syndrome)
A seronegative reactive arthritis triggered by specific genitourinary or enteric infections in genetically susceptible individuals.
- Classic Triad: Arthritis, conjunctivitis, and urethritis.
- Etiology: Triggered by Chlamydia, Mycoplasma, Salmonella, Shigella, or Yersinia infections.
- Clinical Features:
- Asymmetric poly- or oligoarthritis affecting knees and ankles, appearing 2–6 weeks post-infection.
- Mucocutaneous lesions include painless buccal ulcers, keratoderma blennorrhagica on the soles/palms, and circinate balanitis.
- HLA-B27 is present in 70-80% of patients.
- Treatment: Primarily NSAIDs, intra-articular steroids, and short-term antibiotics if an active infection persists.
3. Psoriatic Arthritis (PsA)
An inflammatory arthropathy occurring in 5-20% of patients with psoriasis, affecting axial and peripheral joints, nails, skin, and entheses.
- Clinical Patterns (Moll and Wright):
- Oligo-articular disease (asymmetric large/small joints).
- Distal interphalangeal (DIP) joint involvement with nail pitting.
- Arthritis mutilans (severe deforming arthritis with massive phalangeal destruction).
- Symmetric polyarthropathy resembling rheumatoid factor-negative RA.
- Psoriatic spondylitis (axial disease).
- Classification & Imaging:
- Diagnosed using the CASPAR criteria (requires inflammatory articular disease + score ≥ 3 from skin psoriasis, nail lesions, dactylitis, negative RF, and juxta-articular bone formation).
- Radiography shows pencil-in-cup changes, periostitis, and asymmetric syndesmophytes.
- Treatment Strategy:
- Mild disease: NSAIDs or apremilast.
- Moderate to severe peripheral arthritis: Conventional DMARDs like Methotrexate (MTX).
- Severe disease or axial involvement: TNF inhibitors or IL-17 inhibitors (secukinumab).
📊 Visual Learning
💡 Important Points to Remember
- Hallmark Back Pain: SpA back pain is insidious, occurs before age 40, lasts > 3 months, and improves with exercise (unlike mechanical back pain which worsens with activity).
- HLA-B27 Association: Highly positive in Ankylosing Spondylitis (90-95%) and Reiter's syndrome (70-80%), but less prevalent in axial psoriatic arthritis (~30%).
- X-Ray vs. MRI: Plain X-rays show late changes (syndesmophytes, bamboo spine, ankylosis), whereas MRI detects early bone marrow edema and inflammation.
- DIP Joint Involvement: Psoriatic arthritis frequently involves distal interphalangeal (DIP) joints, a feature typically spared in rheumatoid arthritis.
- Uveitis Management: For AS patients with concurrent inflammatory bowel disease or uveitis, monoclonal antibody TNF inhibitors are strongly preferred over etanercept.
- Systemic Steroids Discouraged: Systemic glucocorticoids are strongly discouraged for spinal disease in AS.
- Common Confusion: Do not confuse the symmetric sacroiliitis of Ankylosing Spondylitis with the asymmetric sacroiliitis seen in Reiter's syndrome and psoriatic spondylitis.
- CASPAR Criteria: Memorize that diagnosing Psoriatic Arthritis requires inflammatory articular disease plus at least 3 points from specific clinical/dermatological/radiological domains.
⚠️ Common Exam Questions
- MCQ Trick on Back Pain: Examiners will describe a young patient with back pain and ask for the best next step. They will try to trick you by offering "complete bed rest"—remember that exercise improves SpA symptoms, so rest worsens them!
- Imaging Question: A question might test the earliest modality to detect sacroiliitis. The trap is choosing an X-ray; the correct answer for early detection is MRI because radiographic joint damage takes years to develop.
- RF in Seronegative SpA: Questions frequently test laboratory profiles. Remember that Rheumatoid Factor (RF) is negative in all seronegative spondyloarthropathies.
- Treatment Algorithm Trap: For psoriatic arthritis with severe erosive disease, examiners will test if you know to skip conventional DMARDs and immediately start a TNF inhibitor to prevent irreversible joint destruction.
📝 Quick Review Checklist
I can explain the clinical features and diagnostic criteria of Ankylosing Spondylitis
I understand the classic triad and infectious triggers of Reiter's syndrome
I can define the CASPAR criteria and radiographic findings of Psoriatic Arthritis
I know the role of HLA-B27 across the different seronegative spondyloarthropathies
I know the stepwise pharmacological management from NSAIDs to biologic agents