What are the clinical and radiologic features of spinal spondylosis and its initial management?

Ankylosing Spondylitis: Clinical and Radiologic Features

Clinical Features

Ankylosing spondylitis (AS) presents with inflammatory back pain that is fundamentally different from mechanical low back pain, and recognizing this distinction is critical for early diagnosis. 1

Inflammatory Back Pain Characteristics

• Morning stiffness lasting more than 30 minutes that improves with activity but not with rest 1
• Night pain that disrupts sleep and is not relieved by rest 1
• Age of onset before 45 years (>96% of cases start before age 40) 1
• Insidious onset with symptoms persisting for more than 3 months 1
• Improvement with exercise and worsening with rest, which is the opposite pattern of mechanical pain 1

Diagnostic Probability

• When inflammatory back pain is present in a patient with chronic low back pain, the post-test probability of axial spondyloarthropathy increases to 14% 1
• Approximately 75% of AS patients exhibit inflammatory back pain as a leading symptom 1

Extra-Spinal Manifestations

• Peripheral arthritis affecting large joints, particularly lower extremities 1
• Enthesitis (inflammation at tendon/ligament insertion sites) 1
• Acute anterior uveitis and other extra-articular features 1

Radiologic Features

Initial Imaging Approach

Conventional radiography of the sacroiliac (SI) joints and symptomatic spine regions is the recommended first-line imaging modality for suspected AS. 1

Sacroiliac Joint Changes

• Bilateral sacroiliitis is the radiographic hallmark, though it may take several years of inflammation before visible on plain films 1
• Erosions, sclerosis, and eventual ankylosis of the SI joints develop progressively 1
• MRI detects early inflammatory changes (bone marrow edema) before radiographic damage appears, making it essential when radiographs are negative but clinical suspicion remains high 1

Spinal Changes

• Syndesmophytes (vertical bony bridges connecting vertebral bodies) are pathognomonic for AS 1
• "Bamboo spine" appearance results from complete bridging syndesmophytes and ossification of spinal ligaments 1
• Squaring of vertebral bodies due to erosion of anterior vertebral corners 1
• Facet joint ankylosis and ossification of interspinous ligaments 1

MRI Findings in Active Disease

• Vertebral corner inflammatory lesions (bone marrow edema) on STIR or fat-suppressed T2 sequences 1
• Fatty marrow deposition at sites of previous inflammation, which predicts future syndesmophyte formation 1
• Enthesitis at disc-vertebral junctions and posterior spinal elements 1
• Gadolinium enhancement is not routinely required for initial assessment; STIR sequences are sufficient to detect inflammation 1

Imaging Protocol Recommendations

When to Image

• Initial evaluation: Plain radiographs of SI joints and symptomatic spine areas 1
• If radiographs are negative: MRI of SI joints should be the next step to identify pre-radiographic disease 1
• Spine MRI: May be helpful when other imaging is negative; the request should specify evaluation for axial spondyloarthropathy so sequences can be modified to include fat suppression 1

MRI Technical Requirements

• STIR or fat-suppressed T2-weighted sequences are essential for detecting inflammatory changes 1
• Standard lumbar spine protocols for disc disease may lack the necessary fat suppression and miss inflammatory features 1
• Contrast enhancement may improve conspicuity of inflammation in discs, facet joints, and entheses at initial assessment but is not required for follow-up 1

Monitoring Structural Progression

• Conventional radiography remains the primary method for long-term monitoring of structural damage 1
• Radiographs should not be repeated more frequently than every 2 years unless clinically indicated 1
• Baseline cervical and lumbar spine radiographs in established AS are recommended to detect syndesmophytes, which predict development of new syndesmophytes 1

Critical Clinical Pitfall: Spinal Fractures

Patients with ankylosis of the spine have a high incidence of unstable fractures from seemingly minor trauma, and a high clinical suspicion is mandatory when these patients present with new spine pain. 1

Fracture Imaging Protocol

• Multiplanar CT is required to exclude fracture in any patient with spinal ankylosis and pain after trauma, even from low-energy mechanisms such as a fall from standing 1
• Conventional radiographs have poor sensitivity for fractures in ankylosed spines 1
• MRI without contrast should be added if neurologic symptoms are present to evaluate spinal cord, nerve root, and ligamentous injuries 1
• Many fractures involve all three spinal columns and are unstable, with high rates of neurologic injury 1

Initial Management

Conservative Therapy

• NSAIDs should be taken regularly once diagnosis is established, not just as needed 1
• Physiotherapy is a cornerstone of management 1

Biologic Therapy Indications

• TNF-alpha blocking agents (infliximab, etanercept) show strong efficacy for active disease refractory to NSAIDs and physiotherapy 1
• Approximately 50% of patients achieve 50% improvement in disease activity with anti-TNF therapy 1
• 72% of patients with disease duration <10 years show at least 50% improvement, emphasizing the importance of early diagnosis 1
• Extensive MRI inflammatory activity (bone marrow edema), particularly in the spine, predicts good clinical response to anti-TNF therapy and may aid in treatment decisions 1

Screening Parameters for Early Diagnosis

To identify the 5% of chronic low back pain patients who have axial spondyloarthropathy, use these parameters in patients with back pain >3 months and onset before age 45: 1

• Inflammatory back pain (sensitivity 75%, post-test probability 14%) 1
• HLA-B27 positivity when combined with clinical features 1
• MRI evidence of sacroiliitis when radiographs are negative 1
• Elevated inflammatory markers (ESR, CRP) support but do not confirm diagnosis 1