What is the best approach to diagnose and treat back arthritis in a patient, considering their age, medical history, and lifestyle?

Evaluating Back Arthritis: A Structured Diagnostic Approach

Begin with plain radiographs of the sacroiliac joints and HLA-B27 testing for patients under age 45 with chronic back pain (≥3 months) showing inflammatory characteristics, as this combination provides the most cost-effective initial screening for axial spondyloarthritis. 1, 2

Initial Clinical Assessment

Identify Inflammatory vs. Mechanical Back Pain

The critical first step is determining whether back pain has inflammatory characteristics, which occur in 70-80% of axial spondyloarthritis patients 2:

• Onset before age 40-45 years with insidious (not traumatic) beginning 1, 2
• Morning stiffness lasting >30-60 minutes that improves with activity 2, 3
• Improvement with exercise but NOT with rest (opposite of mechanical pain) 1, 2
• Night pain, particularly awakening in the second half of the night 2
• Alternating buttock pain indicating sacroiliac joint involvement 2
• Duration ≥3 months to distinguish from acute conditions 1, 2

Screen for Extra-Articular Manifestations

Look for associated features that increase diagnostic probability 2:

• Uveitis (inflammatory eye disease) 2
• Psoriasis 2
• Peripheral arthritis affecting large joints (especially knees) in asymmetric, oligoarticular pattern in 30-50% of patients 2
• Inflammatory bowel disease 2
• Family history of spondyloarthritis (sensitivity 25%, specificity 96%) 1

Rule Out Red Flags Immediately

Perform focused neurological examination to exclude emergent conditions 4:

• Cauda equina syndrome: urinary retention, fecal incontinence, saddle anesthesia—requires urgent MRI and surgical evaluation 5, 4
• Progressive motor weakness or sensory deficits 4
• Cancer: history of malignancy, unexplained weight loss, age >50, failure to improve after 1 month 5
• Infection: fever, IV drug use, recent infection 5
• Compression fracture: older age, osteoporosis, corticosteroid use 5

Initial Laboratory and Imaging Strategy

First-Line Testing (Age <45, Chronic Pain ≥3 months)

Order HLA-B27 testing and plain radiographs of sacroiliac joints together 1, 2:

• HLA-B27: 90% sensitivity, 90% specificity, likelihood ratio 9, post-test probability 32% 1
• Plain radiographs of sacroiliac joints: 80% sensitivity, 80% specificity, likelihood ratio 4, post-test probability 17% 1
• Do NOT rule out spondyloarthritis based solely on negative HLA-B27, as 11-26% of patients are HLA-B27 negative 2

Inflammatory Markers (Limited Utility)

• ESR/CRP: Only 50% sensitivity, 80% specificity—not reliable for screening 1
• Elevated inflammatory markers may be absent in active axial spondyloarthritis 2

When to Advance to MRI

Order MRI of sacroiliac joints without contrast if 1, 2:

• Plain radiographs are negative or equivocal AND clinical suspicion remains high 2
• Disease activity is unclear or clinical/laboratory data are conflicting 1
• Knowledge of MRI findings would alter treatment decisions (e.g., considering TNF-inhibitor therapy) 1
• MRI has 90% sensitivity and 90% specificity for detecting bone marrow edema indicating active inflammation 1

Key MRI considerations 1:

• Noncontrast and contrast-enhanced MRI have similar diagnostic utility for sacroiliac joints 1
• Extensive MRI inflammatory activity (bone marrow edema), particularly in the spine, predicts good response to anti-TNF therapy (likelihood ratio 6.7 for BASDAI50 response with Berlin spine score >11) 1
• SPARCC MRI score ≥2 for either sacroiliac joints or spine associated with better adalimumab response 1

Avoid Routine Follow-Up Imaging

Do NOT perform routine radiographic follow-up 1:

• American College of Rheumatology recommends against routine radiographic monitoring given lack of proven benefit 1
• Structural changes evolve slowly, requiring ≥2 years to detect progression 1
• Repeat imaging only when findings would change management or for patient counseling on prognosis 1

MRI follow-up is NOT standardized 1:

• No standard method exists for monitoring treatment response or disease progression 1
• Degree of MRI inflammation correlation with disease activity is variable 1
• Consider repeat MRI only when disease activity is unclear or findings would alter treatment 1

Differential Diagnosis Considerations

Distinguish from Lumbar Disc Herniation

• Radiculopathy: pain radiating down leg in nerve root distribution, positive straight-leg raise (91% sensitivity), worsening with positional changes 5
• 90% of symptomatic disc herniations occur at L4/L5 and L5/S1 levels 5
• Most improve within 4 weeks with conservative management 5, 4

Distinguish from Spinal Stenosis

• Pseudoclaudication (not pain worsening after standing from sitting) 5
• More common in patients >65 years (only 3% of back pain patients) 5

Distinguish from Rheumatoid Arthritis

• RA spinal involvement typically affects cervical spine, not sacroiliac joints 6
• Distal interphalangeal, sacroiliac, and lumbar spine joints rarely involved in RA 3
• Symmetric erosive disease with hand involvement (metacarpophalangeal, proximal interphalangeal joints) 3

Common Pitfalls to Avoid

• Do NOT delay diagnosis waiting for radiographic sacroiliitis—average diagnostic delay is 4.9-8 years from symptom onset 2
• Do NOT use ultrasound for sacroiliac joint evaluation—limited to superficial posterior margins and not validated for routine diagnosis 1
• Do NOT order MRI for mechanical back pain without red flags—imaging does not improve outcomes and incurs unnecessary expense 5, 4
• Do NOT assume normal inflammatory markers exclude inflammatory arthritis—CRP/ESR elevated in only 50% of cases 1

Referral Criteria to Rheumatology

Refer when 1, 2:

• Positive HLA-B27 with high clinical suspicion (inflammatory back pain features) 2
• Radiographic or MRI evidence of sacroiliitis in patient <45 years with chronic back pain 1, 2
• Extra-articular manifestations (uveitis, psoriasis, inflammatory bowel disease) with back pain 2
• Inflammatory back pain features present with post-test probability ≥14% based on clinical parameters 1