Ankylosing Spondylitis: A Comprehensive Overview

Abstract

Ankylosing spondylitis (AS) is a chronic, immune-mediated inflammatory disorder that primarily affects the axial skeleton, leading to pain, stiffness, and progressive spinal fusion. Strongly associated with the HLA-B27 gene, AS is a subtype of spondyloarthropathies and has systemic manifestations beyond the musculoskeletal system. Early diagnosis and appropriate treatment are crucial to prevent structural damage and disability. This article provides an in-depth review of the etiology, clinical features, diagnostic modalities, and therapeutic strategies for managing ankylosing spondylitis.

Introduction

Ankylosing spondylitis is a form of seronegative spondyloarthritis characterized by inflammation of the sacroiliac joints and spine. The term “ankylosis” refers to joint stiffness due to abnormal adhesion and rigidity of bones, and “spondylitis” refers to inflammation of the vertebrae. The disease predominantly affects young males and has a significant impact on quality of life.

Epidemiology

  • Prevalence: Around 0.1%–1.4% globally; varies by ethnicity and prevalence of HLA-B27.
  • Gender: Male-to-female ratio is approximately 3:1.
  • Age of Onset: Typically between 15 and 35 years.

Etiology and Pathogenesis

  • Genetic Factors: The HLA-B27 gene is found in over 90% of patients with AS. However, its presence alone is not sufficient for disease development.
  • Immunological Factors: Dysregulated immune response leads to chronic inflammation, primarily in the axial skeleton.
  • Environmental Triggers: Infections (e.g., Klebsiella pneumoniae) may play a role in genetically predisposed individuals.

Pathologically, inflammation begins at the entheses (sites where ligaments and tendons attach to bone), leading to erosions and subsequent ossification—resulting in the hallmark feature: bamboo spine on imaging.

Clinical Features

Axial Symptoms:

  • Chronic low back pain and stiffness, worse in the morning or after inactivity (inflammatory back pain)
  • Progressive limitation of spinal mobility
  • Stooped posture due to thoracic kyphosis

Peripheral Symptoms:

  • Arthritis of hips, shoulders, and knees
  • Enthesitis (e.g., Achilles tendonitis, plantar fasciitis)
  • Dactylitis (sausage fingers/toes)

Extra-Articular Manifestations:

  • Ocular: Anterior uveitis (most common)
  • Cardiac: Aortitis, conduction abnormalities
  • Pulmonary: Apical fibrosis
  • Renal: Secondary amyloidosis

Diagnosis

Modified New York Criteria (1984):

  1. Clinical Criteria:
    • Low back pain >3 months improved with exercise
    • Limitation of lumbar spine motion
    • Limited chest expansion
  2. Radiologic Criteria:
    • Bilateral sacroiliitis grade ≥2 or unilateral sacroiliitis grade ≥3

Diagnosis requires at least one clinical and one radiologic criterion.

Investigations:

  • Laboratory:
    • Elevated ESR, CRP
    • HLA-B27 testing
    • Negative rheumatoid factor and anti-CCP
  • Imaging:
    • X-ray: Sacroiliitis, bamboo spine
    • MRI: Early inflammation of sacroiliac joints
    • CT: Structural damage

Differential Diagnosis

  • Mechanical back pain
  • Rheumatoid arthritis
  • Psoriatic arthritis
  • Reactive arthritis
  • Diffuse idiopathic skeletal hyperostosis (DISH)

Management

Non-Pharmacological:

  • Patient Education: Emphasis on posture and physical activity
  • Physiotherapy: Core strengthening, spinal mobility exercises
  • Smoking cessation: Smoking worsens spinal damage

Pharmacological:

  • NSAIDs: First-line for pain and inflammation
  • TNF-alpha inhibitors (e.g., etanercept, infliximab): For refractory cases
  • IL-17 inhibitors (e.g., secukinumab): Emerging option
  • DMARDs: For peripheral arthritis (e.g., sulfasalazine)
  • Corticosteroids: Limited use

Surgical Management:

  • Joint replacement (e.g., hip arthroplasty)
  • Corrective spinal osteotomy in severe kyphosis

Prognosis

  • Variable course; some patients remain stable, others progress to significant disability.
  • Early treatment improves outcomes.
  • Life expectancy is normal with good disease control, though complications (cardiac, respiratory, amyloidosis) can affect morbidity.

Conclusion

Ankylosing spondylitis is a debilitating but manageable chronic inflammatory disease. Early diagnosis, patient-centered care, and a multidisciplinary approach are key to improving long-term outcomes. With the advent of biologics, the disease trajectory has significantly improved, offering hope for better quality of life in affected individuals.

Modern HealthMe