What is the initial approach to evaluating and treating a patient presenting with back pain?

Differential Diagnosis for Back Pain

Primary Diagnostic Categories

The vast majority of back pain (>85%) is nonspecific mechanical low back pain, but your evaluation must systematically exclude serious pathology through targeted history and physical examination focused on red flags. 1

The American College of Physicians classifies low back pain into three broad categories that guide your diagnostic approach: 1

• Nonspecific mechanical low back pain (>85% of cases) - musculoligamentous pain without identifiable structural cause 1
• Back pain with radiculopathy or spinal stenosis (7% combined) - herniated disc with radiculopathy (4%) or spinal stenosis (~3%) 1
• Back pain with specific underlying pathology (<2% combined) - serious conditions requiring urgent intervention 1

Red Flag Conditions Requiring Immediate Consideration

You must actively screen for these serious conditions because delayed diagnosis worsens outcomes: 2

Cauda Equina Syndrome (0.04% prevalence)

• Urinary retention, fecal incontinence, saddle anesthesia, and motor deficits at multiple levels 1
• Requires immediate MRI or CT and urgent neurosurgical consultation 3

Vertebral Malignancy (0.7% prevalence)

• History of cancer increases posttest probability from 0.7% to 9% (positive likelihood ratio 14.7) 1
• Unexplained weight loss, age >50, failure to improve with conservative therapy 3
• Consider plain radiography or ESR (≥20 mm/h has 78% sensitivity, 67% specificity) with MRI for abnormalities 2

Spinal Infection (0.01% prevalence)

• Fever, recent infection, IV drug use, or immunocompromised status 1
• Midline tenderness with fever suggests vertebral infection 3
• Obtain CBC, urinalysis, ESR, and MRI if suspected 4

Vertebral Compression Fracture (4% prevalence)

• History of osteoporosis, steroid use, or significant trauma 2
• Midline tenderness in high-risk patients 3
• Plain radiography is appropriate initial imaging 2

Ankylosing Spondylitis/Axial Spondyloarthritis (0.3-5% in chronic low back pain)

• Age <45 years, morning stiffness >30 minutes that improves with movement and worsens with rest 1
• Inflammatory pain pattern distinguishes this from mechanical pain 1
• Early diagnosis critical as TNF-blocking agents show strong efficacy when disease duration <10 years 1

Radiculopathy and Spinal Stenosis

Herniated Disc with Radiculopathy (4% prevalence)

• Sciatica with associated paraspinal muscle spasm 1
• Positive straight leg raise test, dermatomal sensory changes, motor weakness in specific nerve root distribution 3
• Most improve within 4 weeks with noninvasive management 1

Spinal Stenosis (3% prevalence)

• Pseudoclaudication (leg pain with walking that improves with rest or forward flexion) 1
• Bilateral leg symptoms, older age 3
• Most improve within 4 weeks with noninvasive management 1

Clinical Approach to Differentiation

Use pain pattern characteristics to guide your differential: 1

• Mechanical pain pattern (worsens with activity, improves with rest) → nonspecific mechanical low back pain with myofascial involvement 1
• Inflammatory pain pattern (morning stiffness >30 minutes, improves with movement, worsens with rest) → spondyloarthritis 1
• Neurologic symptoms (radicular pain, motor weakness, sensory deficits) → radiculopathy or spinal stenosis 1

Imaging Strategy

Do not routinely obtain imaging in patients with nonspecific low back pain without red flags, as this does not improve outcomes and may lead to unnecessary interventions. 2, 1

When to Image Immediately:

• Severe or progressive neurologic deficits 2
• Suspected cauda equina syndrome 2
• Suspected cancer with impending spinal cord compression 2
• Suspected vertebral infection 2
• MRI is preferred over CT (avoids radiation, better soft tissue visualization) 2, 3

When to Consider Delayed Imaging:

• Plain radiography for suspected vertebral compression fracture in high-risk patients (osteoporosis, steroid use) 2
• Plain radiography may be reasonable for persistent symptoms after 4-6 weeks of conservative therapy without red flags 2, 3
• Consider imaging at 1 month for persistent, unimproved symptoms 2

Psychosocial Risk Factors for Chronicity

Assess for yellow flags that predict poorer outcomes and chronic disability: 2

• Depression, passive coping strategies, job dissatisfaction 2
• Higher disability levels, disputed compensation claims, somatization 2
• Use STarT Back tool at 2 weeks to risk-stratify patients and direct resources appropriately 3

Critical Pitfalls to Avoid

• Routine imaging for uncomplicated acute low back pain exposes patients to unnecessary radiation without clinical benefit (single lumbar spine x-ray equals daily chest x-ray for >1 year in gonadal radiation) 2, 1
• Overlooking inflammatory causes in younger patients (<45 years) with chronic symptoms and morning stiffness delays access to highly effective TNF-blocking agents 1
• Failing to recognize cauda equina syndrome leads to permanent neurologic disability from delayed surgical decompression 2
• Missing cancer in patients with prior malignancy - the posttest probability jumps from 0.7% to 9% in this population 1