What are the clinical presentation, diagnosis, and treatment options for a patient with sacroiliitis, potentially with a history of inflammatory bowel disease, psoriatic arthritis, or ankylosing spondylitis?

Sacroiliitis: Clinical Presentation, Diagnosis, and Treatment

Clinical Presentation

Sacroiliitis typically presents with inflammatory back pain characterized by insidious onset before age 45 years, chronic duration ≥3 months, improvement with exercise but not rest, and night pain awakening patients in the second half of the night. 1

Key Clinical Features

• Inflammatory back pain with prolonged morning stiffness lasting >30 minutes 1
• Alternating buttock pain indicating sacroiliac joint involvement 1
• Direct palpation tenderness over the sacroiliac joints on examination 1
• Pain that improves within 2 days of NSAID therapy 2
• Symptoms often worse at night, particularly awakening in the second half of sleep 1

Associated Conditions

Sacroiliitis occurs in the context of several inflammatory conditions:

• Inflammatory bowel disease (IBD): Radiological sacroiliitis occurs in 20-50% of patients with ulcerative colitis and Crohn's disease, though progressive ankylosing spondylitis develops in only 1-10% 2, 3
• Ankylosing spondylitis: The classic cause of bilateral sacroiliitis, more common in males 2, 3
• Psoriatic arthritis: Part of the spondyloarthropathy spectrum 2
• Reactive arthritis: Following gastrointestinal or genitourinary infections 4

Critical pitfall: Axial arthropathy in IBD typically runs independent of intestinal disease activity, unlike peripheral arthritis 2, 3. This means sacroiliitis can be active even when bowel disease is quiescent.

Diagnosis

Clinical Assessment and Referral Criteria

Refer to rheumatology when patients have back pain onset before age 45 years lasting >3 months PLUS at least 4 of the following: back pain before age 35, waking at night to alleviate symptoms, buttock pain, improvement with movement or within 2 days of NSAIDs, first-degree family member with spondyloarthritis, or current/previous arthritis, enthesitis, or psoriasis 2. Refer with only 3 criteria if HLA-B27 positive 2.

Imaging Algorithm

Start with plain radiographs of the sacroiliac joints in patients with mature skeletons 2:

• Diagnostic criteria: Sacroiliitis grade ≥2 bilaterally or grade ≥3 unilaterally on x-ray meets modified New York criteria (sensitivity 66%, specificity 68%) 1
• Limitation: Radiographs may be normal in early disease 2, 5

If radiographs are normal but clinical suspicion remains high, proceed to MRI 2:

• MRI sequences required: At minimum, coronal oblique T1-weighted, fluid-sensitive sequences (STIR or fat-saturated T2-weighted), perpendicular axial oblique sequence, and a sequence for bone-cartilage interface evaluation 6
• Diagnostic finding: Active inflammation showing bone marrow edema on fluid-sensitive sequences (sensitivity 78%, specificity 88%) 1
• Early detection: MRI identifies early sacroiliitis in symptomatic patients with normal plain radiography (non-radiographic spondyloarthritis) 2, 1

Important caveat: Bone marrow edema on MRI lacks specificity and occurs in up to 30% of healthy controls, postpartum patients, and athletes 3. Interpretation must be in clinical context with typical skeletal sites (anterior chest wall, spine, mandible) 2.

Alternative imaging when MRI unavailable: Low-dose CT is reasonable, particularly for evaluating structural lesions and erosions 6. Dual-energy CT with virtual non-calcium images can depict bone marrow edema 6. Avoid scintigraphy due to lack of specificity 5.

Laboratory Testing

• HLA-B27: Found in 74-89% of axial spondyloarthritis but only 25-75% of IBD patients with ankylosing spondylitis and 7-15% with isolated sacroiliitis 2, 3. HLA-B27 is unreliable as a diagnostic test in IBD patients due to lower prevalence than idiopathic ankylosing spondylitis 2, 3
• ESR: Elevated in only 50% of ankylosing spondylitis patients, limiting utility 1
• CRP: May be elevated but not consistently 2

Differential Diagnosis

Must exclude 2:

• Infectious osteomyelitis: Fever, chills, presumable port of entry, solitary lesion, significantly elevated CRP/ESR, bacteremia
• Psoriatic arthritis: Psoriasis, nail dystrophy, dactylitis, juxta-articular new bone formation
• Rheumatoid arthritis: Symmetrical polyarthritis, anti-CCP or RF positivity
• Osteoarthritis: Older onset, subchondral sclerosis, osteophytes
• Septic sacroiliitis: Spread to muscles on MRI 5

Treatment

Initial Management

All patients with confirmed sacroiliitis should be referred to rheumatology for structured exercise program and subspecialist management 2, 1.

First-line pharmacologic treatment is NSAIDs at the lowest effective dose 2:

• Trial for 2-4 weeks 2
• If ineffective, switch to another NSAID 2
• NSAIDs are conditionally recommended as adjunct therapy 2
• Consider adding hydrotherapy for pain 2

Disease-Modifying Therapy

For active sacroiliitis, initiate DMARDs before biologics in most patients 2:

• Methotrexate is preferred over leflunomide or sulfasalazine 2
• Subcutaneous methotrexate preferred over oral formulation 2
• Sulfasalazine may be used, particularly in IBD-associated disease 2

Escalate to biologic therapy if inadequate response to DMARDs:

• TNF inhibitors are the primary biologic option for refractory disease 2
• Secukinumab (IL-17A inhibitor) is FDA-approved for ankylosing spondylitis and non-radiographic axial spondyloarthritis 7:
  • Dosing: 150 mg subcutaneous with or without loading (weeks 0,1,2,3,4), then every 4 weeks 7
  • ASAS20 response: 58-61% at week 16 vs 28% placebo 7
  • ASAS40 response: 38-41% at week 52 vs 19% placebo 7

Adjunctive Therapies

• Intraarticular corticosteroids conditionally recommended as adjunct 2
• Triamcinolone hexacetonide strongly preferred over triamcinolone acetonide for injections 2
• Bridging oral corticosteroids (<3 months) conditionally recommended during DMARD initiation in high disease activity 2

Interventional Options for Refractory Cases

For mechanical SI joint pain not responding to medical management 8:

• Corticosteroid injections
• Prolotherapy
• Radiofrequency ablation
• SI joint fusion surgery (last resort)

Monitoring and Complications

Screen for acute anterior uveitis: Immediate ophthalmology referral for eye pain or redness 2. Uveitis is more common in women with spondyloarthritis 2.

Multidisciplinary management: Complex extra-intestinal manifestations should be discussed in multidisciplinary team meetings 2.