AS Quick Guide

Definition

Chronic inflammatory arthritis primarily affecting the spine and sacroiliac joints.

Epidemiology

  • 2:1 male predominance
  • Onset typically 20-30 years
  • 90-95% onset before age 45
  • Strong HLA-B27 association

Key Features

  • Inflammatory back pain
  • Morning stiffness >30 min
  • Improves with exercise
  • Alternating buttock pain
  • Enthesitis
  • Dactylitis

Extra-articular

  • Anterior uveitis (25-30%)
  • Psoriasis
  • Inflammatory bowel disease
  • Cardiac involvement

Diagnosis

  • Clinical suspicion
  • HLA-B27 testing
  • Elevated CRP/ESR
  • X-ray/MRI sacroiliitis

Management

  • NSAIDs first-line
  • Physiotherapy
  • Biologic DMARDs
  • Exercise programs

Complications

  • Spinal fusion
  • Fractures
  • Osteoporosis
  • Uveitis
  • Cardiac disease
  • Pulmonary fibrosis

Ankylosing Spondylitis

Chronic inflammatory arthritis primarily affecting the axial skeleton

Core Features

Axial Manifestations

  • Chronic inflammatory back pain
  • Sacroiliitis (often bilateral)
  • Progressive spinal ankylosis
  • Reduced spinal mobility

Peripheral Manifestations

  • Asymmetric oligoarthritis
  • Enthesitis (Achilles, plantar fascia)
  • Dactylitis ("sausage digits")

Systemic Features

  • Fatigue
  • Low-grade fever
  • Weight loss

Inflammatory Back Pain Characteristics

  • Age of onset <40 years
  • Insidious onset
  • Duration >3 months
  • Morning stiffness >30 minutes
  • Improves with exercise
  • No improvement with rest
  • Night pain (often second half)

Risk Factors & Epidemiology

Demographics

  • Male predominance (2:1)
  • Typical onset 20-30 years
  • Rare onset after age 45

Genetic Factors

  • HLA-B27 present in 90-95%
  • Family history in 10-20%
  • ERAP1 gene association

Environmental Triggers

  • Gut microbiome changes
  • Previous GI infections
  • Smoking (worse prognosis)

Diagnostic Approach

Clinical Assessment

Investigations

Laboratory Tests

  • HLA-B27 (90-95% positive)
  • CRP/ESR (elevated in 50-70%)
  • Mild anemia of chronic disease
  • Negative RF and ACPA

Imaging

  • X-rays:
    • Sacroiliitis (grade ≥2 bilaterally)
    • Vertebral squaring
    • Syndesmophytes
    • Bamboo spine (late)
  • MRI: Detects early inflammation

Referral Criteria to Rheumatology

Refer if inflammatory back pain plus ≥1 of:

  • HLA-B27 positive
  • Family history of spondyloarthritis
  • Psoriasis
  • IBD
  • Uveitis
  • Good response to NSAIDs
  • Elevated CRP

Differential Diagnosis

Mechanical Back Pain

  • Improves with rest
  • No morning stiffness
  • No systemic symptoms

Other Spondyloarthropathies

  • Psoriatic arthritis
  • Reactive arthritis
  • Enteropathic arthritis

Other Inflammatory

  • Rheumatoid arthritis
  • Diffuse idiopathic skeletal hyperostosis (DISH)
  • Osteitis condensans ilii

Management

Non-Pharmacological

Pharmacological

First-line

  • NSAIDs (full dose, continuous)
  • PPI cover if GI risk

Second-line

  • Biologic DMARDs (TNF inhibitors, IL-17 inhibitors)
  • Conventional DMARDs for peripheral arthritis

Symptomatic

  • Simple analgesia
  • Corticosteroid injections

Monitoring Requirements

  • Disease activity (BASDAI)
  • Spinal mobility measures
  • NSAID toxicity monitoring
  • Biologic therapy screening
  • Bone density assessment

Complications

Musculoskeletal

  • Spinal fusion (bamboo spine)
  • Vertebral fractures
  • Osteoporosis
  • Atlantoaxial subluxation

Ocular

  • Anterior uveitis (25-30%)
  • Secondary glaucoma
  • Cataract

Cardiovascular

  • Aortitis
  • Aortic regurgitation
  • Conduction abnormalities
  • Increased CVD risk

Pulmonary

  • Restrictive lung disease
  • Apical fibrosis
  • Pleural thickening

Neurological

  • Cauda equina syndrome
  • Spinal cord compression

Renal

  • IgA nephropathy
  • Amyloidosis (rare)

Prognosis & Follow-up