Is intervertebral disc desiccation seen in patients with ankylosing spondylitis?

Intervertebral Disc Desiccation in Ankylosing Spondylitis

Yes, intervertebral disc desiccation can be seen in patients with ankylosing spondylitis (AS), but it is not a primary characteristic feature of the disease. Rather, AS is primarily characterized by inflammation at entheses (where ligaments and tendons attach to bone), particularly at the sacroiliac joints, with progressive ossification leading to ankylosis.

Imaging Features in Ankylosing Spondylitis

Primary Spinal Manifestations

• Sacroiliitis: The hallmark feature, visible on radiographs as erosions, sclerosis, joint space narrowing, and eventually ankylosis 1, 2
• Syndesmophytes: Bony outgrowths at vertebral corners
• Vertebral body squaring
• Shiny corners (Romanus lesions)
• Spinal ankylosis (bamboo spine) in advanced disease

Disc-Related Changes

• While intervertebral disc involvement is not the primary feature of AS, the disease process can affect the discs in several ways:
  • Inflammation at the discovertebral junction can occur 1
  • The nucleus pulposus tends to be spared in the disease process, which can actually allow disc herniation to occur in the heavily ossified spine 3
  • Ossification can extend to involve the intervertebral discs in advanced disease 4

Imaging Modalities for Assessment

MRI Findings

• MRI is essential for identifying early inflammatory disease 1
• Requires specific sequences:
  • T1-weighted sequences
  • Fat-suppressed fluid-sensitive sequences (T2-weighted fat-suppressed or STIR images) 2
  • Standard spinal MRI protocols for evaluation of disc disease may not include the fat suppression of the T2 imaging necessary for sensitivity for the inflammatory features of axial spondyloarthritis 1

Radiographic Findings

• Conventional radiography is the first-line imaging modality for initial evaluation 1, 2
• Can show structural changes including erosions, sclerosis, and ankylosis
• Should not be repeated more frequently than every 2 years for monitoring 1

CT Findings

• CT demonstrates structural changes that may not be apparent on radiographs 1
• Particularly useful for evaluation of the thoracic spine and facet joints 1
• Essential for assessment of spinal fractures in patients with ankylosis 1, 5

Clinical Implications

Spinal Fracture Risk

• Patients with ankylosis of the spine have a high incidence of unstable fractures that may occur from seemingly minor trauma 1, 5
• These fractures often involve all 3 columns of the spine and are unstable 5
• High associated rate of neurologic injury 5, 6
• CT with multiplanar reformatted images is necessary for exclusion of fracture in a patient with ankylosis and pain after trauma 1

Diagnostic Pitfalls

• Over-reliance on radiographs alone, which may miss early disease 2
• Misinterpreting normal inflammatory markers (ESR/CRP can be normal in up to 50% of cases) 2
• Delayed diagnosis (average 7-10 years from symptom onset) 2
• Important to distinguish inflammatory changes from degenerative changes, as both inflammatory and fatty lesions can occur in degenerative changes 1

Treatment Considerations

• NSAIDs are first-line treatment for axial spondyloarthritis 2
• TNF inhibitors are recommended over secukinumab or ixekizumab as the first biologic to be used 1, 2
• Regular assessment of disease activity using validated tools like ASDAS-CRP is recommended 2

In summary, while intervertebral disc desiccation is not a primary feature of ankylosing spondylitis, the disease process can affect the intervertebral discs through inflammation, ossification, and altered biomechanics of the spine. The primary focus in imaging assessment should be on identifying sacroiliitis, syndesmophytes, and other characteristic features of the disease.