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Differential Diagnosis of Back Pain

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Overview: Three Broad Categories

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1. Mechanical / Musculoskeletal (~97%)

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2. Nonmechanical Spinal Conditions (~1%)

Neoplastic (~0.7%)

• Metastatic carcinoma — most common (breast, prostate, lung, kidney, thyroid)
• Multiple myeloma
• Lymphoma / leukemia
• Primary vertebral tumors (e.g., osteoid osteoma, giant cell tumor)
• Spinal cord / intradural tumors
• Retroperitoneal tumors

Suspect in: age >50, history of cancer, pain worse at night or supine, unexplained weight loss.

Infectious (~0.1%)

• Vertebral osteomyelitis — Staph aureus most common; fever, ↑ ESR/CRP
• Septic discitis
• Epidural / paraspinous abscess — urgent: can compress cord
• Herpes zoster — radicular pain may precede rash by days

Risk factors: IV drug use, immunosuppression, recent bacteremia, spinal procedures.

Inflammatory Arthritis (~0.3%)

• Ankylosing spondylitis — young male; insidious onset; morning stiffness >1 h; improves with activity; ↑ with rest (opposite of mechanical)
• Psoriatic spondylitis
• Reactive arthritis (Reiter syndrome)
• Rheumatoid arthritis (cervical spine involvement)
• IBD-associated spondyloarthropathy

Other Nonmechanical Spinal

• Paget disease of bone
• Osteochondrosis
• Arachnoiditis — chronic pain after intrathecal procedure or surgery

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3. Referred / Visceral Pain (~2%)

Vascular (Can Be Immediately Life-Threatening)

• Abdominal aortic aneurysm (AAA) — mid/low back pain radiating to hips; pulsatile mass; do not miss
• Aortic dissection — sudden tearing chest-to-back pain
• Spinal arteriovenous malformation — progressive myelopathy + pain
• Spinal cord infarction

Renal / Urologic

• Nephrolithiasis — colicky flank pain radiating to groin; hematuria
• Pyelonephritis — fever, CVA tenderness, dysuria
• Perinephric abscess

Gastrointestinal

• Pancreatitis — epigastric pain radiating to the back (L1 region); ↑ amylase/lipase
• Cholecystitis — mid-thoracic/right shoulder referred pain
• Penetrating peptic ulcer
• Diverticulitis

Pelvic / Gynecologic

• Endometriosis — cyclical low back/sacral pain
• Ectopic pregnancy — acute lower back/pelvic pain in reproductive-age women
• Pelvic inflammatory disease (PID)
• Prostatitis — sacral/perineal aching

Cardiac / Pulmonary

• Myocardial ischemia / infarction (rare back presentation)
• Pulmonary embolism / pleural disease — pleuritic mid-back pain

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Neurological Causes (Classified Separately)

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Red Flags — Prompt Imaging / Urgent Workup

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A Quick Clinical Framework

1. Pain location + radiation: Axial only → mechanical; dermatomal radiation → radiculopathy; non-dermatomal referred → visceral
2. Age: <20 → spondylolysis, tumor (Ewing's); 20–50 → disc herniation, spondyloarthropathy; >50 → degenerative, metastases, osteoporotic fracture
3. Onset: Acute after exertion → strain/disc; acute at rest → vascular/infectious; insidious → inflammatory or neoplastic
4. Aggravating/relieving factors: ↑ with activity + ↓ with rest → mechanical; ↑ with rest + ↓ with activity → inflammatory; pain at night → tumor/infection
5. Neurological exam: Always assess for motor weakness, sensory level, reflexes, and bowel/bladder function

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Management of Low Back Pain & When to Investigate

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Guiding Principles

1. Identify and manage the small minority with serious ("red flag") pathology
2. Avoid unnecessary investigations in uncomplicated cases
3. Keep the patient active and functioning

"Mechanical low back pain, even with radicular symptoms, resolves without specific intervention within 30 days in most patients and within 3 months in 90% of patients." — Goldman-Cecil Medicine

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Classification by Duration

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Step 1: Initial Assessment — Screen for Red Flags

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Non-Pharmacological Management (First-Line for All)

1. Activity Continuation (most important)

• Do not prescribe bed rest — patients resuming normal activities (using pain as the limiting factor) recover faster than those on bed rest
• Withhold formal exercise programs until the acute episode has significantly improved

2. Physical Therapy & Exercise

• Core-strengthening exercises, targeted physiotherapy for subacute/chronic LBP
• Yoga, tai chi, water gymnastics — all show beneficial effects for chronic LBP
• Exercise alone or combined with education is effective at preventing recurrence
• The effect of physiotherapy alone is modest but real

3. Heat / Cold

• Heat wrap provides moderate improvement in pain and function for acute LBP
• Evidence favors heat over cold
• Temporary symptomatic relief only

4. Spinal Manipulation (Chiropractic / Osteopathic)

• More helpful for acute than chronic LBP
• Small benefit; noninferior to other recommended physical therapies
• Not recommended as sole treatment

5. Massage

• Beneficial for acute and chronic LBP, especially soft tissue/spasmodic pain
• Benefits tend to be short-lived

6. Acupuncture

• Modest, short-lived benefit for both acute and chronic LBP
• Effects wane without continued therapy

7. Psychological Therapies (especially for Chronic LBP)

• Cognitive-behavioural therapy (CBT) — strongest evidence
• Mindfulness-based stress reduction, biofeedback, operant therapy
• High co-prevalence with depression (33–67%) and anxiety (10–30%) — address these
• Biopsychosocial model: identify psychosocial "yellow flags" (catastrophisation, fear-avoidance, low job satisfaction) that predict chronicity

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Pharmacological Management

Acute LBP

Chronic LBP (>3 months)

"Opioid analgesics should not be prescribed for chronic back pain from the ED." — Tintinalli's Emergency Medicine

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Interventional Procedures

Epidural corticosteroids are for radicular symptoms only — they have no role in nonspecific axial back pain.

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Surgical Management

RCT evidence shows lumbar spinal fusion for non-radicular degenerative LBP is only modestly helpful compared with no treatment and not beneficial compared with an active physiotherapy programme. Surgery should not be offered for non-specific LBP without clear structural target.

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When to Investigate

Do NOT investigate routinely

• Uncomplicated, nonspecific acute LBP without red flags
• Monitor for 4–6 weeks before pursuing further diagnostics
• Routine imaging is not associated with improved outcomes and findings are often incidental

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Blood Tests — Indicated When:

Elevated ESR + CRP should prompt imaging — raises suspicion for spinal epidural abscess, osteomyelitis, discitis, or malignancy.

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Imaging — When to Order:

Summary: Imaging is indicated when:

• Any neurological deficit (motor, sensory, reflex, bowel/bladder)
• Red flags present (suspected malignancy, infection, fracture)
• No improvement after 4–6 weeks of adequate conservative treatment
• Considering interventional procedure or surgery (to identify target)

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Radiculopathy — Additional Points

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Prognosis

• 90% of acute LBP resolves within 3 months without specific intervention
• 50% will have recurrence within 1 year
• Risk factors for chronicity: obesity, low education, tobacco use, high initial pain severity, somatisation tendency, job dissatisfaction, heavy lifting at work, psychopathology

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