What examination should be done next for a patient with morning back pain that improves with movement and a positive Schober test, suggestive of ankylosing spondylitis (AS) or other spondyloarthropathies?

Eye Examination for Uveitis (Option A)

The next examination should be an eye examination to screen for uveitis, as this patient's clinical presentation is highly suggestive of axial spondyloarthritis (ankylosing spondylitis), and uveitis is the most common extra-articular manifestation, occurring in up to 40% of patients. 1, 2

Clinical Reasoning

This patient presents with classic inflammatory back pain features that strongly suggest axial spondyloarthritis:

• Morning stiffness improving within an hour after movement - characteristic of inflammatory rather than mechanical back pain 1, 2
• Positive Schober test - indicates reduced lumbar spine mobility, consistent with spondyloarthropathy 1
• Pain pattern worsening in morning and improving with activity - distinguishes inflammatory from mechanical causes 1, 3

The combination of these features yields a high likelihood of axial spondyloarthritis, making screening for associated extra-articular manifestations the appropriate next step. 1, 2

Why Eye Examination is the Priority

Acute anterior uveitis is reported in up to 40% of patients with ankylosing spondylitis and represents the most frequent extra-articular manifestation. 1, 2 This is a potentially sight-threatening condition that requires:

• Early detection to prevent complications including vision loss 2
• Prompt ophthalmologic referral if identified 1
• Recognition that uveitis may precede, coincide with, or follow the onset of musculoskeletal symptoms 4, 5

Why Not the Other Options

CNS examination for weakness (Option B) is not indicated as a routine next step because:

• Neurologic deficits are not typical presenting features of uncomplicated axial spondyloarthritis 1
• Neurologic complications occur late in disease, typically with advanced spinal ankylosis and fractures 1
• The patient's presentation suggests early inflammatory disease, not advanced disease with complications 1

CVS examination for mitral regurgitation (Option C) is not the priority because:

• While aortic valve involvement occurs in up to 80% of patients with ankylosing spondylitis, aortic regurgitation is the cardiac manifestation, not mitral regurgitation 1
• Cardiac involvement typically occurs in long-standing disease, not at initial presentation 1
• Uveitis is far more common (40%) than clinically significant cardiac disease in early presentation 1, 2

Appropriate Diagnostic Workup After Eye Examination

Following the eye examination, the diagnostic evaluation should include:

• Plain radiographs of sacroiliac joints as the first imaging modality 1
• HLA-B27 testing - positive in 74-89% of patients with axial spondyloarthritis, with a post-test probability of 32% when positive in chronic back pain patients 1, 2, 6
• Inflammatory markers (ESR/CRP) - though normal in 50% of cases, so cannot rule out disease if negative 1, 3, 6
• MRI of sacroiliac joints if radiographs are negative or equivocal, as MRI can detect early inflammatory changes before structural damage appears 1, 3

Critical Clinical Pearls

• Do not delay evaluation for extra-articular manifestations - uveitis screening should occur early in the diagnostic process 2
• The diagnosis of axial spondyloarthritis is frequently delayed by 5-8 years from symptom onset, emphasizing the importance of recognizing inflammatory back pain patterns early 2, 6
• Inflammatory back pain is present in 70-80% of patients with axial spondyloarthritis and includes: onset before age 45, morning stiffness >30 minutes, improvement with exercise but not rest, night pain (especially second half of night), and alternating buttock pain 1, 2, 7
• Refer to rheumatology for definitive diagnosis and management, particularly if HLA-B27 positive, imaging shows sacroiliitis, or symptoms persist despite NSAIDs 1, 6