What are the X-ray signs of inflammatory back pain?

X-ray Signs of Inflammatory Back Pain

Radiographic evaluation of sacroiliac joints is the first-line imaging modality for suspected inflammatory back pain, with key findings including erosions, sclerosis, joint space alterations, and ankylosis, though it has limited sensitivity (19-72%) for early disease detection. 1

Key Radiographic Findings in Inflammatory Back Pain

Sacroiliac Joint Findings

• Erosions: Irregularities of the joint margins, particularly on the iliac side
• Sclerosis: Increased bone density adjacent to the joint, especially on the iliac side
• Joint space alterations: Initially widening due to cartilage inflammation, later narrowing
• Ankylosis: Bony fusion across the joint in advanced disease 1

Spinal Findings

• Syndesmophytes: Bony outgrowths at vertebral corners
• Erosions: Irregularities at vertebral corners
• Shiny corners (Romanus lesions): Areas of reactive sclerosis at vertebral corners
• Vertebral body squaring: Loss of normal concavity of anterior vertebral bodies
• Ankylosis: Fusion of vertebral segments in advanced disease 1

Limitations of Radiography

Radiography has significant limitations for detecting early inflammatory back pain:

• Low sensitivity (19-72%) and variable specificity (47-84.5%) 1
• Misses more than half of patients with structural changes when compared to CT 1
• 41.3% of radiography reports give incorrect diagnoses when CT is used as reference 2
• Fair to moderate interobserver agreement for radiographic findings 1

Imaging Algorithm for Inflammatory Back Pain

1. Initial Evaluation: Radiographs of sacroiliac joints and symptomatic areas of the spine 1, 2

   • Include anteroposterior view of the whole pelvis 2
   • For spine, at minimum include cervical and lumbar spine radiographs 1

2. If radiographs are negative or equivocal but clinical suspicion remains high:

   • MRI of sacroiliac joints is the next appropriate imaging method 1, 2
   • MRI can detect inflammatory changes 3-7 years before radiographic evidence 2
   • Include T1 sequences and fat-suppressed fluid-sensitive sequences (T2-weighted fat-suppressed or STIR) 1

3. If sacroiliac joint MRI is negative but axial spondyloarthritis is still suspected:

   • MRI of the spine may be helpful, as isolated spine involvement occurs in 1-49% of cases 1
   • Sagittal imaging is best for evaluation of axial spondyloarthritis spinal lesions 1

4. CT consideration:

   • CT of sacroiliac joints (without contrast) may be helpful when equivocal radiographic abnormalities exist 1
   • CT better demonstrates complex anatomy and subtle erosions 1

Clinical Pitfalls and Caveats

• Thoracic spine radiographs have limited utility due to overlying structures; MRI or CT is preferred for thoracic spine evaluation 1
• Relying solely on radiographs may lead to missed diagnoses in early disease 2
• Ultrasound, bone scintigraphy, and PET/CT are not routinely recommended for initial evaluation 2
• The presence of two or more corner inflammatory lesions on MRI has a sensitivity of 69% and specificity of 94% for ankylosing spondylitis 1
• Inflammatory back pain is a concept describing clinical characteristics rather than a diagnosis itself 3

Remember that about one-third of patients with recent-onset inflammatory back pain show inflammation, and about one-sixth show structural changes in at least one sacroiliac joint on MRI 4. MRI is the most sensitive method (89%) for detecting acute or chronic changes in patients with inflammatory back pain and normal or indeterminate findings on plain radiographs 5.