What are the clinical features and treatment options for ankylosing spondylitis?

Ankylosing Spondylitis: Clinical Features and Treatment

Ankylosing spondylitis is a chronic inflammatory arthritis characterized by sacroiliitis, enthesitis, and progressive spinal fusion, with first-line treatment being NSAIDs combined with physical therapy, escalating to TNF inhibitors when NSAIDs fail to control active disease. 1, 2

Clinical Features

Cardinal Symptoms

• Inflammatory back pain is the hallmark feature, improving with exercise but worsening at rest, particularly in the morning 2
• Morning stiffness of the spine with prolonged duration is typical 2
• Chronic back pain lasting more than 3 months that improves with exercise but is not relieved by rest 3

Physical Examination Findings

• Limitation of lumbar spine motion in both sagittal and frontal planes 3
• Reduced chest expansion relative to age and sex-matched normal values 3
• Sacroiliitis universally present, with radiographic changes forming the core of the modified New York criteria (bilateral grade ≥2 or unilateral grade 3-4) 1, 3
• Enthesitis at sites where tendons and ligaments attach to bone 1

Structural Changes

• Spinal ankylosis with marked propensity for sacroiliac joint and spinal fusion 1, 2
• Excessive spinal bone formation resulting from untreated enthesial inflammation leading to fibrosis and eventual ossification 2
• Kyphotic deformities in advanced disease 4

Genetic and Epidemiologic Features

• HLA-B27 positivity in 90-95% of patients, though only 1% of HLA-B27 carriers develop the disease 2
• Prevalence of 0.1-0.5% in the general population, with early forms reaching 0.2-1% 2
• Diagnostic delay averages 5-7 years between first symptoms and diagnosis 2

Treatment Approach

First-Line Pharmacological Treatment

NSAIDs are the first-line pharmacological treatment for patients with pain and stiffness, with strong level Ib evidence showing improvement in spinal pain, peripheral joint pain, and function over 6 weeks. 1, 2, 5

• Continuous NSAID use is recommended during active disease periods 1, 6
• For patients with increased gastrointestinal risk, use either non-selective NSAIDs plus gastroprotective agents or selective COX-2 inhibitors 5
• Phenylbutazone is historically considered the NSAID of choice, though other NSAIDs provide similar benefits and selection should be patient-specific 6

Non-Pharmacological Treatment (Mandatory Concurrent Therapy)

Physical therapy and regular exercise are fundamental treatments that must be combined with pharmacological interventions. 1, 2, 5

• Home exercise programs improve function in the short term compared to no intervention 5
• Group therapy shows better patient global assessment outcomes than individual therapy alone 5
• Complex individualized programs including posture reeducation, manual spinal mobilization, pelvic/extremity exercises, and stretching significantly reduce pain intensity and spine stiffness over 3 months 7
• Patient education about the condition and self-management strategies is essential 2, 5

Second-Line Treatment: TNF Inhibitors

TNF inhibitors are indicated for patients with persistently high disease activity (BASDAI >4 for >4 weeks) despite NSAID treatment. 1, 2

• Rapid and strong effect on almost all aspects of active disease, including acute phase reactants, function, spinal mobility, peripheral arthritis, enthesitis, and MRI-detected inflammation 2
• Response criteria: 50% improvement in BASDAI or absolute change of 20 mm (on 0-100 scale) plus expert opinion favoring continuation 2
• Monoclonal antibody TNF inhibitors (not etanercept) should be preferentially used in patients with concomitant inflammatory bowel disease or recurrent iritis 1
• Secukinumab (IL-17A inhibitor) at 150 mg subcutaneously demonstrates ASAS20 responses of 61% and ASAS40 responses of 36% at Week 16 8

Adjunctive Therapies

• Analgesics (paracetamol) and opioids may be considered when NSAIDs are insufficient, contraindicated, or poorly tolerated 5
• Local corticosteroid injections directed to sites of musculoskeletal inflammation (enthesopathy, sacroiliac joints) may be beneficial 5, 6
• Systemic glucocorticoids should NOT be used for axial disease due to lack of evidence and potential side effects 1, 5

Disease-Modifying Antirheumatic Drugs (DMARDs)

• Sulfasalazine is effective primarily in patients with peripheral joint involvement, showing improvement in clinical and laboratory indices 6, 9
• Methotrexate requires further controlled studies to establish efficacy 6
• DMARDs are considered for longstanding severe or refractory disease 6

Surgical Interventions

Total hip arthroplasty should be performed in patients with refractory pain or disability and radiographic evidence of advanced hip arthritis. 1, 5

• Spinal corrective osteotomy and stabilization may be valuable in selected patients with severe kyphotic deformities 5, 4
• Preoperative considerations include proper interruption of DMARDs considering half-lives, bone quality assessment, and careful airway management evaluation 4

Treatment Goals and Monitoring

Primary Goals

• Reduce symptoms and maintain spinal flexibility and normal posture 1
• Reduce functional limitations and maintain work ability 1
• Decrease disease complications and prevent structural damage 1, 2

Disease Activity Assessment

• Active disease definition: Disease activity >4 weeks AND BASDAI >4 (on 0-10 scale) 3
• Core assessment parameters: Pain (VAS for spine pain day/night), morning stiffness duration and intensity (up to 120 minutes), fatigue level, patient global assessment 3
• Functional measures: BASFI (Bath Ankylosing Spondylitis Functional Index) 3
• Spinal mobility: Modified Schober test, chest expansion, occiput-to-wall distance, lateral lumbar flexion 3
• Laboratory: High-sensitivity CRP levels 3

Monitoring Frequency

• Radiographic monitoring generally not needed more often than every 2 years, except in rapidly progressing cases 5
• Assessment should include disease activity, pain, function, disability, structural damage, and comorbidities 5

Common Pitfalls

• Overreliance on imaging without clinical correlation leads to unnecessary interventions 5, 3
• Failure to incorporate both pharmacological and non-pharmacological approaches limits treatment effectiveness 5
• Delayed diagnosis due to difficulty distinguishing inflammatory from mechanical back pain contributes to the average 5-7 year diagnostic delay 2, 10
• Neglecting extra-articular manifestations including uveitis, inflammatory bowel disease, and psoriasis 3
• Inadequate screening for cardiovascular risk and osteoporosis in established disease 3