What is the diagnosis and treatment for sacroilitis?

Diagnosis and Treatment of Sacroiliitis

Diagnosis

Start with conventional radiography of the sacroiliac joints as the first-line imaging modality in most patients with suspected sacroiliitis, but proceed directly to MRI in young patients or those with short symptom duration. 1

Initial Imaging Approach

• Conventional radiography (X-ray) of the sacroiliac joints is rated as the most appropriate initial imaging study (rating 9/9) 1
• Spine radiography should be performed as a complementary examination to evaluate for syndesmophytes and other spinal involvement 1
• Radiographs demonstrate structural consequences of inflammation but often lag 7+ years behind symptom onset, limiting sensitivity in early disease 1

When Radiographs Are Negative or Equivocal

If clinical suspicion remains high despite negative or equivocal radiographs, MRI of the sacroiliac joints is the next essential step and should not be delayed. 1

MRI Protocol Requirements

• Mandatory sequences: Coronal oblique T1-weighted, fluid-sensitive sequences (STIR or T2 fat-saturated), perpendicular axial oblique sequence, and a joint-line-specific sequence for bone-cartilage interface evaluation 2
• Evaluate both inflammatory and structural lesions: Active inflammatory lesions (primarily bone marrow edema) and structural lesions (erosions, new bone formation, sclerosis, fat infiltration) 1
• Contrast administration: Gadolinium-enhanced sequences may improve detection of subtle inflammatory lesions initially but have not been shown to significantly increase diagnostic accuracy and are not routinely necessary 1

MRI Diagnostic Performance

• MRI demonstrates sensitivity of 79-82% and specificity of 89-97% for axial spondyloarthritis diagnosis 1
• Bone marrow edema is the primary inflammatory finding but can occur in degenerative changes, postpartum patients, athletes, and up to 30% of healthy controls—requiring careful interpretation 1
• Combined erosion and/or bone marrow edema increases sensitivity to 96-98% compared to bone marrow edema alone (83-91%) without reducing specificity 1

Alternative Imaging When MRI Unavailable

• CT without contrast (rating 7/9) can identify subtle erosions and structural damage, especially useful when MRI is contraindicated 1
• Low-dose CT is preferred given patients are often young 2
• Dual-energy CT with virtual non-calcium images can depict bone marrow edema 2
• Scintigraphy and ultrasound are NOT recommended for diagnosing sacroiliitis 1

Spine MRI Considerations

• Not generally recommended for initial diagnosis of axial spondyloarthritis 1
• May be helpful when sacroiliac joint imaging is negative but clinical suspicion persists, as isolated spine involvement occurs in 6-23% of cases 1
• Must include fluid-sensitive sequences (STIR or T2 fat-saturated) as standard disc disease protocols may lack necessary fat suppression 1

Clinical Context for Diagnosis

• Typical presentation: Age <45 years, chronic back pain (≥3 months), inflammatory symptoms (morning stiffness, improvement with exercise, pain in second half of night, alternating buttock pain) 1
• Diagnosis requires expert rheumatologist evaluation combining clinical features, HLA-B27 status, C-reactive protein, and imaging findings 1
• Classification criteria alone do not suffice for diagnosis—must exclude alternative diagnoses 1

Pediatric Considerations

• Critical caveat: Normal developmental features in children (flaring, blurring, irregular articular surfaces) can simulate disease and must be recognized to avoid misdiagnosis 2

Treatment

Non-Pharmacological Management

Physical therapy and exercise remain essential throughout all disease phases regardless of pharmacological treatment. 1

Pharmacological Treatment Algorithm

First-Line: NSAIDs and Conservative Measures

• Physical therapy combined with NSAIDs for symptom relief 3
• Analgesics for pain management 3

Second-Line: Interventional Procedures for Refractory Cases

• Corticosteroid injections into the sacroiliac joint 3
• Prolotherapy for ligamentous stabilization 3
• Radiofrequency ablation for nerve-mediated pain 3

Biologic DMARDs for Axial Spondyloarthritis

For patients with confirmed axial spondyloarthritis and elevated CRP or inflammation on MRI who fail conservative treatment, TNF inhibitors or IL-17 inhibitors are indicated. 1

• TNF inhibitors approved for both radiographic and non-radiographic axial spondyloarthritis (except infliximab, which is approved only for radiographic disease) 1
• IL-17 inhibitors approved for axial spondyloarthritis with radiographic sacroiliitis only 1
• Elevated CRP and/or MRI inflammation predicts clinical efficacy of biologics in both radiographic and non-radiographic disease 1
• Use ASDAS (Ankylosing Spondylitis Disease Activity Score) to assess disease activity, treatment response, and continuation decisions 1

Surgical Intervention

• Sacroiliac joint fusion surgery reserved for cases where conservative and interventional methods fail to provide significant relief 3

Monitoring and Follow-Up

• MRI of sacroiliac joints and/or spine may be used to assess and monitor disease activity, providing additional information beyond clinical and biochemical assessments 1
• STIR sequences are sufficient for detecting inflammation; contrast medium not needed for monitoring 1
• Conventional radiography for long-term monitoring of structural damage should not be repeated more frequently than every 2 years 1

Critical Pitfall

Patients with radiographic sacroiliitis only (without syndesmophytes), normal CRP, and no MRI inflammation may not be good candidates for biologic therapy—consider potential misdiagnosis given poor reliability of radiographic sacroiliac joint assessment. 1