What is the recommended approach for a spondyloarthropathy workup?

Spondyloarthropathy Workup

Begin with clinical assessment for inflammatory back pain (onset before age 40, insidious onset, improvement with exercise, no improvement with rest, night pain), peripheral arthritis pattern (asymmetric, lower limb predominant), enthesitis, dactylitis, and extra-articular manifestations (uveitis, psoriasis, inflammatory bowel disease), then proceed to HLA-B27 testing and sacroiliac joint imaging with MRI as the primary modality for early disease detection. 1

Clinical Assessment Components

Inflammatory Back Pain Criteria

• Assess for five key features: age of onset <40 years, insidious onset, improvement with exercise but not rest, pain at night with improvement upon getting up, and morning stiffness >30 minutes 2, 3
• Document duration of morning stiffness and response to activity, as these distinguish inflammatory from mechanical pain 2
• Evaluate for alternating buttock pain, which suggests sacroiliitis 2, 4

Peripheral Joint and Entheseal Examination

• Look for asymmetric oligoarthritis predominantly affecting lower limbs (knees, ankles, feet), which is the characteristic peripheral pattern distinct from rheumatoid arthritis 2, 5, 4
• Examine for enthesitis at Achilles tendon insertions, plantar fascia, and pelvic attachments, as enthesitis is the fundamental pathologic lesion in spondyloarthropathies 2, 3
• Check for dactylitis ("sausage digits") in fingers or toes 2

Extra-Articular Manifestations

• Screen for acute anterior uveitis (eye pain, photophobia, blurred vision), which occurs in 25-40% of patients and requires urgent ophthalmology referral 2, 6
• Examine skin for psoriatic plaques, nail pitting, or onycholysis 2, 3
• Obtain history of inflammatory bowel disease symptoms (chronic diarrhea, abdominal pain, blood in stool) 2, 5

Laboratory Testing

HLA-B27 Testing

• Order HLA-B27 as a useful adjunctive test, recognizing it is positive in 90-95% of ankylosing spondylitis but also present in 6-8% of the general population 5, 3
• Interpret HLA-B27 in clinical context only—it supports but does not confirm diagnosis 5

Inflammatory Markers

• Measure ESR and CRP, though recognize these may be normal in up to 50% of active spondyloarthropathy cases 1, 5
• Use CRP or ESR for regular monitoring if elevated at baseline 1

Rheumatoid Factor

• Confirm rheumatoid factor negativity, as seronegative arthritis is a defining feature of spondyloarthropathies 5, 6

Imaging Strategy

Initial Sacroiliac Joint Imaging

• Order MRI of the sacroiliac joints as the primary imaging modality for suspected early axial spondyloarthropathy, as it detects active inflammation (bone marrow edema) before structural changes appear on radiographs 1, 3
• Use STIR (short tau inversion recovery) or T2-weighted fat-suppressed sequences to identify bone marrow edema, which indicates active sacroiliitis 1
• Recognize that bone marrow edema lesions can occur in 23% of individuals without spondyloarthropathy, particularly in mechanical stress zones, so correlate findings with clinical presentation 1

Conventional Radiography

• Obtain AP pelvis radiographs to assess for structural sacroiliitis (erosions, sclerosis, joint space narrowing, ankylosis) if MRI unavailable or to document established disease 1
• Do not rely solely on radiographs for early diagnosis, as structural changes may take 5-10 years to develop 3
• Order lumbar and cervical spine radiographs in established ankylosing spondylitis to detect syndesmophytes, which predict future syndesmophyte development 1

Imaging Modalities NOT Recommended

• Avoid scintigraphy and ultrasound for diagnosis of sacroiliitis, as they lack sufficient sensitivity and specificity 1
• CT may provide additional structural information if MRI cannot be performed, but exposes patients to radiation 1

Structured Reporting Requirements

When Imaging Shows Equivocal Findings

• Radiologists should communicate uncertainty clearly rather than using vague terms like "likely" or "suspicious," and provide rationale for their conclusion 1
• Request differential diagnoses with probability assessments, especially if alternative diagnoses are more likely than spondyloarthropathy 1
• If findings are inconclusive, radiologists should suggest further imaging (e.g., CT to evaluate for erosions when MRI shows isolated mechanical zone edema) 1

Incidental Findings

• If axial spondyloarthropathy features are detected on imaging ordered for other indications, the radiologist should recommend rheumatology referral for formal assessment 1

Disease Activity Monitoring

Clinical Measures

• Use validated composite measures regularly: BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) plus acute phase reactants, or ASDAS (Ankylosing Spondylitis Disease Activity Score) 1
• Measure BASFI (Bath Ankylosing Spondylitis Functional Index) to assess functional impact 1
• Frequency of assessment depends on disease activity—monthly to every 3 months for active disease, every 6-12 months for stable disease 1

Follow-up Imaging

• Do not obtain repeat spine radiographs at scheduled intervals (e.g., every 2 years) as standard practice in stable patients, as there is no evidence this improves outcomes 1
• Do not obtain MRI to confirm disease inactivity in clinically stable patients, given lack of evidence for improved outcomes and risk of overtreatment 1
• Consider MRI only when disease activity level is unclear and results would change treatment decisions 1

Critical Pitfalls to Avoid

• Do not dismiss normal inflammatory markers—up to 50% of active spondyloarthropathy patients have normal ESR/CRP 5
• Do not over-interpret isolated bone marrow edema in mechanical stress zones on MRI without supporting clinical features and structural lesions 1
• Do not delay rheumatology referral when clinical suspicion is high despite negative initial imaging, as early treatment with biologics is most effective 3
• Recognize that HLA-B27 negativity does not exclude spondyloarthropathy—10% of ankylosing spondylitis patients are HLA-B27 negative 3