What else could be causing low back pain and stiffness that improves with movement?

Differential Diagnosis for Low Back Pain with Morning Stiffness Improving with Movement

The clinical presentation of low back pain and stiffness that improves with movement is most consistent with inflammatory back pain, specifically axial spondyloarthritis (including ankylosing spondylitis), which affects 0.3-5% of patients with chronic low back pain in primary care settings 1, 2.

Primary Consideration: Axial Spondyloarthritis

The pattern described—pain improving with exercise, morning stiffness, and worsening with rest—forms the classic triad with high specificity for inflammatory causes 2. Key diagnostic features include:

• Age of onset before 45 years with insidious symptom development 1
• Morning stiffness lasting more than 1 hour that improves with activity 1, 2
• Pain that awakens the patient during the second half of the night 1, 2
• Alternating buttock pain suggesting sacroiliac joint involvement 1
• Duration of symptoms exceeding 3 months 1

The prevalence of ankylosing spondylitis ranges from 0.3% to 5% in primary care patients with chronic low back pain, with higher rates when inflammatory features are present 1, 2.

Other Inflammatory Conditions to Consider

Psoriatic Arthritis and Reactive Arthritis

• These spondyloarthropathies share the HLA-B27 association and can present with sacroiliitis, inflammatory arthritis, and the same pattern of morning stiffness improving with activity 1
• Look for associated psoriatic skin lesions, nail changes, or history of preceding infection 1

Inflammatory Bowel Disease-Related Spondyloarthropathy

• Axial involvement occurs in patients with Crohn's disease or ulcerative colitis 1
• Inquire about gastrointestinal symptoms including diarrhea, bleeding, or abdominal pain 1

Mechanical Causes That May Mimic This Pattern

Spinal Stenosis

• Can present with neurogenic claudication—leg pain and weakness with walking or standing that is relieved by sitting or spinal flexion 3
• However, spinal stenosis typically worsens with activity rather than improves, distinguishing it from inflammatory causes 3
• Affects approximately 3% of patients presenting with low back pain 1

Symptomatic Disc Herniation

• Present in approximately 4% of primary care patients with low back pain 1
• Usually presents with radicular symptoms in a specific nerve root distribution rather than the diffuse stiffness pattern described 4

Critical Red Flags Requiring Immediate Evaluation

When evaluating any patient with this presentation, screen for:

• Cauda equina syndrome: urinary retention (90% sensitivity), fecal incontinence, saddle anesthesia, motor deficits at multiple levels 1, 4
• Malignancy: history of cancer (increases probability from 0.7% to 9%), unexplained weight loss, failure to improve after 1 month, age >50 years 1, 4
• Spinal infection: fever, recent infection, intravenous drug use, immunocompromised status 4
• Compression fracture: older age, osteoporosis history, corticosteroid use 4

Diagnostic Approach

Initial Imaging

• Plain radiographs of the sacroiliac joints and lumbar spine are the first-line imaging modality 1
• Radiographic findings often lag 7+ years behind symptom onset in axial spondyloarthritis 1

Advanced Imaging When Radiographs Are Negative

• MRI of the sacroiliac joints is the next appropriate step when inflammatory back pain is suspected with negative radiographs 1, 2
• MRI can detect bone marrow edema and inflammatory changes before structural damage appears on radiographs 1, 2
• Use fluid-sensitive sequences (T2-weighted fat-saturated or STIR) to identify characteristic bone marrow lesions 1

Laboratory Testing

• HLA-B27 testing and C-reactive protein support the diagnosis when combined with clinical and imaging findings 1

Common Pitfalls to Avoid

• Do not assume all morning stiffness is inflammatory—mechanical causes can have some morning stiffness, but it typically lasts <30 minutes and worsens with continued activity 2
• Do not delay MRI imaging when clinical suspicion for axial spondyloarthritis is high despite negative radiographs, as early diagnosis enables treatment with TNF-blocking agents that are most effective when disease duration is <10 years 2, 5
• Do not overlook extra-articular manifestations including acute anterior uveitis (up to 40% of ankylosing spondylitis patients), aortic valve involvement, and inflammatory bowel symptoms 1

Treatment Implications

Early diagnosis is critical because:

• NSAIDs should be taken regularly (not as needed) once inflammatory back pain is diagnosed 2
• TNF-blocking agents (adalimumab, etanercept) show strong efficacy, particularly when initiated within 10 years of disease onset 2, 5, 6
• Delayed diagnosis can lead to irreversible structural damage and loss of spinal mobility 1