What is the workup and treatment for possible sacroiliitis?

Workup and Treatment of Sacroiliitis

The initial workup for suspected sacroiliitis should begin with plain radiographs of the sacroiliac joints, followed by MRI without contrast if radiographs are negative or equivocal. 1

Diagnostic Workup

Initial Imaging

1. Plain Radiographs (X-rays):

   • X-rays of sacroiliac joints are rated as "usually appropriate" (9/9) for initial evaluation 1
   • X-rays of the spine are also recommended (9/9) as a complementary examination 1
   • Look for joint space narrowing, erosions, sclerosis, and ankylosis

2. Follow-up Imaging (if radiographs are negative or equivocal):

   • MRI of sacroiliac joints without contrast (8/9) is the preferred next step 1
   • MRI with contrast may be helpful for initial evaluation of inflammatory changes (8/9) 1
   • MRI protocol should include:
     • Coronal oblique T1-weighted and fluid-sensitive sequences
     • Perpendicular axial oblique sequence
     • Sequence for optimal evaluation of bone-cartilage interface 2

3. Alternative Imaging (if MRI is contraindicated):

   • CT sacroiliac joints without IV contrast (7/9) may help identify subtle erosions 1
   • Low-dose CT is reasonable when MRI is unavailable, especially for evaluating structural lesions 2
   • Bone scan with SPECT may help localize pain but is generally not helpful for establishing inflammatory diagnosis (4/9) 1

Laboratory Tests

• C-reactive protein (CRP) - elevated CRP is a strong predictor of response to therapy 1
• HLA-B27 testing - positive results have similar significance to positive MRI findings 3
• Complete blood count and inflammatory markers to assess disease activity

Treatment Algorithm

First-Line Treatment

1. NSAIDs:

   • Strongly recommended as initial therapy for active sacroiliac joint pain 4
   • Options include naproxen, ibuprofen, diclofenac, or COX-2 inhibitors
   • Assess response after 2-4 weeks of therapy 4
   • Trial at least 2 different NSAIDs over 4 weeks total before considering biologics 1

2. Physical Therapy:

   • Conditionally recommended throughout treatment 4
   • Focus on pelvic girdle stabilization exercises and active supervised exercise programs
   • Help identify and reduce mechanical factors contributing to microtrauma

Second-Line Treatment (if NSAIDs fail)

1. Local Injections:

   • Corticosteroid injections directed to the site of inflammation 4
   • Diagnostic SI joint blocks with local anesthetic can confirm the SI joint as pain source
   • Consider when at least three physical provocation tests are positive for SI joint dysfunction

2. Biologics (for inflammatory sacroiliitis):

   • TNF inhibitors are strongly recommended when NSAIDs fail 4

     • Options: etanercept, adalimumab, infliximab, golimumab
     • Requirements before starting biologics:
       • High disease activity (ASDAS ≥2.1 or BASDAI ≥4)
       • Failure of standard treatment (at least 2 NSAIDs over 4 weeks)
       • Evidence of inflammation (elevated CRP and/or inflammation on MRI) 1

   • IL-17 inhibitors (secukinumab, ixekizumab) are strongly recommended for patients who fail TNF inhibitors 4

3. DMARDs:

   • Sulfasalazine is conditionally recommended for patients with contraindications to TNF inhibitors, those who have failed TNF inhibitors, or those with concomitant peripheral arthritis 4
   • Methotrexate is NOT recommended for purely axial disease/sacroiliitis 1, 4

4. Short-course Oral Glucocorticoids:

   • Conditionally recommended for less than 3 months 4
   • Most useful in cases of high disease activity, limited mobility, or significant symptoms

Third-Line Treatment (refractory cases)

1. Radiofrequency Ablation:

   • Cooled radiofrequency ablation may provide longer-lasting relief for patients who fail conservative management and injections 4

2. JAK Inhibitors:

   • Strongly recommended when biologics are contraindicated or unavailable 4

3. SI Joint Fusion Surgery:

   • Reserved for patients with:
     • Positive response to SI injection with >75% relief
     • Failure of all nonsurgical treatments
     • Continued or recurrent SIJ pain 4
   • Percutaneous SI arthrodesis preferred over open arthrodesis due to improved safety profile

Monitoring Treatment Response

• Use standardized measures like ASDAS to monitor disease activity 4
• Include patient-reported outcomes, clinical findings, laboratory tests (CRP), and imaging when appropriate
• Regular reassessment of treatment efficacy and adjustment as needed

Important Considerations

• Early diagnosis and treatment are crucial to prevent irreversible structural damage 2
• Both active inflammatory and structural lesions should be described in imaging reports 2
• Knowledge of normal imaging features in children is essential as normal processes can simulate disease 2
• Pyogenic sacroiliitis is the most common cause of acute sacroiliitis and must be ruled out 5