Approaching Chronic Sacroiliitis

1. Understanding the Lesion

• Subchondral bone marrow edema (active inflammation, seen on MRI STIR)
• Erosions and sclerosis
• Joint space narrowing
• Eventual bony ankylosis

2. Clinical Assessment

• Inflammatory back pain: insidious onset, age < 45, duration > 3 months, morning stiffness > 30 min, improves with exercise, not rest, nocturnal pain
• Associated features: uveitis, psoriasis, inflammatory bowel disease, peripheral arthritis, enthesitis, dactylitis
• Family history of spondyloarthropathy

• Direct sacroiliac joint palpation for tenderness
• Provocative tests: FABERE (Patrick's test), Gaenslen's test, pelvis rock - note these lack specificity/sensitivity and may be negative in early disease or late-stage ankylosis
• Lumbar flexion (Schober's test), chest expansion, tragus-to-wall distance
• Enthesitis examination (heel, Achilles)

• HLA-B27: positive in ~90-95% of AS; useful for screening but present in 4-8% of healthy White individuals; a negative result does not exclude diagnosis
• ESR, CRP: elevated in only 50-60% of axSpA; CRP correlates with treatment response and radiographic progression; normal CRP/ESR does not exclude active disease
• Fecal calprotectin if IBD suspected (>90% specificity and sensitivity)
• Mild normochromic anemia in up to 15% of patients
• Firestein & Kelley's Textbook of Rheumatology

3. Imaging

• First-line imaging; graded per Modified New York Criteria
• Insensitive in early disease - definite radiographic changes appear late

• STIR sequences show active bone marrow edema (hyperintense signal)
• T1 sequences show structural damage (erosions, sclerosis, fat metaplasia)
• Active sacroiliitis on MRI predicts later radiographic sacroiliitis and supports early diagnosis

4. Classification Criteria (ASAS)

5. Disease Activity Monitoring

• BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) - patient-reported; score ≥4 indicates active disease
• ASDAS (Ankylosing Spondylitis Disease Activity Score) - includes CRP; preferred by ASAS. Score ≥2.1 = high disease activity; cut-off for biologic initiation
• BASFI - Bath Ankylosing Spondylitis Functional Index for tracking physical function

6. Treatment - ASAS/EULAR Phased Approach

Phase I (All Patients)

1. Physical therapy - exercise, posture training, hydrotherapy. This is the non-pharmacological backbone and remains important throughout the disease course, including established disease (lung function may be adversely affected if neglected)
2. NSAIDs at maximum tolerated dose - first-line pharmacologic treatment; continuous use preferred over on-demand in active disease; evaluate response in 2-4 weeks
3. Education + regular exercise + smoking cessation - for all patients

Phase II (If Phase I Fails)

• Purely axial disease: Start a biologic DMARD (bDMARD) - current first practice is a TNF inhibitor (TNFi)
• Peripheral-predominant disease: Consider local glucocorticoid injection into SI joint (fluoroscopy- or US-guided) and/or sulfasalazine (for peripheral arthritis, less evidence for axial disease)
• If peripheral measures fail or are contraindicated: escalate to TNFi

• Etanercept, infliximab, adalimumab, certolizumab, golimumab

Phase III (TNFi Failure / Second-line Biologics)

• IL-17A inhibitors: Secukinumab, ixekizumab - approved for axSpA, especially useful where TNFi has failed or for patients with prominent skin psoriasis
• JAK inhibitors (tsDMARDs): Tofacitinib, upadacitinib - approved in radiographic axSpA; option when biologics fail or are contraindicated
• Switching between TNFi agents is an option before moving to a different class

7. Specific Scenarios

Non-radiographic axSpA (nr-axSpA)

• Same treatment algorithm as radiographic AS
• TNFi and IL-17 inhibitors are effective when there is objective evidence of inflammation (elevated CRP or active SI joint inflammation on MRI)

SI Joint Injections

• Fluoroscopy- or CT-guided corticosteroid injection into the SI joint provides short-to-medium-term relief
• A 2025 systematic review (PMID 40397173) on sacroiliac joint pain management outlines current interventional approaches

PRP vs. Corticosteroid Injections

• A 2026 systematic review (PMID 42332419) evaluated PRP versus corticosteroid injections for chronic low back pain secondary to sacroiliitis - emerging evidence for PRP as an alternative to steroids

Pyogenic (Septic) Sacroiliitis

• A different entity - acute, with fever, severe pain; seen in postpartum women and IV drug users
• Diagnosis by blood cultures, fluoroscopic fine-needle aspiration, or open biopsy
• Antibiotic therapy for 6 weeks is usually adequate; surgical drainage rarely needed
• Rheumatology, 2-Volume Set (Elsevier, 2022)

Surgery

• Reserved for severe structural damage with functional impairment
• Total hip arthroplasty for hip joint ankylosis
• Spinal osteotomy for severe kyphotic deformity (> 10-15 years of progressive disease)
• Controversy exists about role of bone grafts in surgical SI joint debridement

8. Monitoring and Treat-to-Target

• Target: remission (ASDAS < 1.3) or low disease activity (ASDAS 1.3-2.1)
• Treat-to-target trials have not consistently shown benefit over standard care, though maintaining a disease activity target remains clinically useful for individual patients
• Regular reassessment of ASDAS/BASDAI, function (BASFI), imaging progression
• Watch for extra-articular manifestations: uveitis (refer ophthalmology), IBD, psoriasis
• Cardiovascular risk monitoring (NSAIDs, chronic inflammation both increase CV risk)
• Bone density monitoring - chronic inflammation + limited mobility = osteoporosis risk

Quick Summary Table