Ankylosing Spondylitis

Ankylosing Spondylitis: Study Notes

• Definition: Chronic inflammatory arthritis primarily affecting the axial skeleton (sacroiliac joints and spine). Can lead to bony fusion of the spine over time due to calcification and new bone formation.

Causes & Epidemiology

• Unknown etiology: The exact cause is currently unknown.
• Genetic predisposition: Strongly associated with HLA-B27 (over 95%).
• Immunological factors: Involves inflammatory markers like IL-23, IL-17, and TNF-α
• Environmental factors: Possible link with fecal Klebsiella Aerogenes.
• Demographics: More common in males (3:1 male to female ratio), typically manifesting between ages 20-30.

Clinical Pictures

• Onset: Usually gradual over months or years, with episodic exacerbations.
• Articular symptoms: Commonly presents with recurrent low back pain and stiffness, radiating to the buttocks and posterior thighs. Pain is worse in the morning (early morning stiffness) and improves with movement.
• Progression: Starts in the lumbosacral area, slowly ascending to involve the entire spine over time. Leads to loss of lumbar lordosis, increased kyphosis (hunchback) in the thoracic and cervical spine, and spinal rigidity.
• Secondary conditions: Secondary osteoarthritis and osteoporosis develop, increasing the risk of spinal fracture.

Investigations & Diagnosis

• CBC: Normocytic normochromic anemia may be present.

• ESR and CRP: Usually elevated but can sometimes be normal.

• Sacro-iliac and spine X-ray: Changes develop gradually, even after symptoms appear. Characterized by subchondral erosions, sclerosis, and ultimately fusion of joints; ossification of anterior and lateral spinal ligaments. Eventually may show the classic "bamboo spine".

• Sacro-iliac and spine MRI: Valuable for diagnosis and monitoring disease progression. Can assist with assessment and detection of early changes more effectively than X-rays

• DXA scan: Used to assess for osteoporosis.

• Chest X-ray: May reveal apical lung fibrosis (in some cases).

• Peripheral arthritis: Approximately 40% of patients also develop asymmetrical peripheral oligoarthritis (inflammation in a few large joints) in the knees, hips, and shoulders.

Extra-Articular Features

• Eyes: Acute anterior uveitis (eye inflammation) is a common and significant extra-articular feature (around 25%).
• Cardiovascular: Aortic regurgitation (heart valve problem) is also noted (around 20%)
• Entheses: Affects tendons and ligaments, such as Achilles tendon, plantar fascia, and patellar ligament causing tendinitis or fasciitis.
• Other features: Other possibilities include IBD, pericarditis, arrhythmias, apical lung fibrosis, amyloid. 80% present with prostatitis

Treatment

• Conservative measures: Regular daily back exercises to maintain joint mobility, alleviate pain and stiffness.
• NSAIDs: Primarily used for symptomatic relief of pain.
• Disease-modifying antirheumatic drugs (DMARDs): Methotrexate and sulfasalazine may be used for peripheral arthritis but are not effective for axial involvement.
• Anti-TNF-α therapy: Infliximab (a TNF-α inhibitor) can be administered if previous therapies are unsuccessful, and both peripheral and axial involvement is present.
• Glucocorticoids: Localized treatment for specific conditions like anterior uveitis or plantar fasciitis.