What are the differentials and management for flank and lumbar pain?

Differential Diagnosis and Management of Flank and Lumbar Pain

Initial Diagnostic Approach

Conduct a focused history and physical examination to categorize patients into three groups: (1) nonspecific low back pain (85% of cases), (2) pain with radiculopathy or spinal stenosis, or (3) pain from specific spinal or non-spinal causes requiring urgent evaluation. 1

Critical Red Flags Requiring Immediate Evaluation

• Cauda equina syndrome: Urinary retention (90% sensitivity), fecal incontinence, saddle anesthesia, bilateral motor weakness, or progressive neurologic deficits at multiple levels 1, 2
• Cancer indicators: History of cancer (increases probability from 0.7% to 9%), unexplained weight loss, failure to improve after 1 month, age >50 years 1
• Infection: Fever, IV drug use, recent infection 1
• Compression fracture: Older age, osteoporosis history, steroid use 1
• Ankylosing spondylitis: Younger age, morning stiffness improving with exercise, alternating buttock pain, awakening with back pain in second half of night 1

Non-Spinal Causes to Exclude

Always consider extraurinary and non-spinal etiologies including nephrolithiasis, pancreatitis, aortic aneurysm, endocarditis, or viral syndromes. 1

• Urolithiasis: Most common cause of acute flank pain; presents with acute unilateral flank pain radiating to groin 3, 4
• Small caliceal calculi: Can cause chronic flank pain even without obvious obstruction 5
• Loin pain-hematuria syndrome: Rare entity causing intractable unilateral or bilateral flank pain with hematuria, diagnosed by exclusion 6
• Thoracic disc herniation: Rare but can present as flank pain mimicking urinary disorders 7

Imaging Strategy

For Suspected Serious Pathology

Order prompt MRI (preferred) or CT when severe/progressive neurologic deficits are present or serious conditions (vertebral infection, cauda equina syndrome, cancer with spinal cord compression) are suspected, as delayed diagnosis worsens outcomes. 1

• MRI advantages: No ionizing radiation, superior soft tissue visualization, better evaluation of vertebral marrow and spinal canal 1
• For suspected cancer without spinal cord compression: Consider plain radiography or ESR (≥20 mm/h has 78% sensitivity, 67% specificity) first, reserving MRI for abnormal results 1
• Alternative for cancer history: Proceed directly to MRI given strongest predictor status 1

For Radiculopathy or Spinal Stenosis

Only obtain MRI (preferred) or CT in patients with persistent symptoms who are potential candidates for surgery or epidural steroid injection. 1

• Most lumbar disc herniations improve within 4 weeks with conservative management 1
• Routine imaging does not improve outcomes or affect treatment decisions 1
• Plain radiography cannot visualize discs or accurately assess spinal stenosis 1

For Acute Flank Pain Suggesting Urolithiasis

Unenhanced helical CT is the imaging modality of choice for acute flank pain, with 98-100% sensitivity and specificity for detecting ureteral stones regardless of size, location, or composition. 1, 3

• Identifies extraurinary causes in approximately one-third of patients 3
• No contrast agent needed, completed within 5 minutes 3
• Ultrasound combined with radiography: Alternative approach with 79-90% sensitivity, though decreased for stones <5mm 1

For Known Stone Disease with Recurrent Symptoms

Noncontrast CT remains the reference standard for evaluating recurrent symptoms in patients with known urolithiasis, optimizing dose and minimizing repeat studies. 1

Management Algorithm

For Nonspecific Low Back Pain (>85% of cases)

Advise patients of favorable prognosis with high likelihood of substantial improvement within first month, recommend remaining active rather than bed rest, and provide self-management education. 1

• Remaining active is more effective than bed rest for acute or subacute low back pain 1
• Explain that early routine imaging cannot identify precise cause and does not improve outcomes 1

For Radiculopathy

• Natural history: Most improve within 4 weeks with noninvasive management 1
• Persistent symptoms: Consider discectomy or epidural steroids after failed conservative therapy 1
• Surgical referral: Reserved for persistent radicular symptoms at 12 weeks unresponsive to conservative care 1

For Cauda Equina Syndrome

Immediately refer to emergency service with MRI and neurosurgical access; surgical decompression should ideally occur within 12 hours of symptom onset to optimize functional recovery. 2

• Delayed surgery associated with poorer outcomes, particularly for urinary and intestinal function 2
• Document extent of neurologic deficit, saddle anesthesia, and anal tone 2

For Urolithiasis

• Acute management: Pain control, hydration, observation for spontaneous passage 4
• Complications: Monitor for hydronephrosis and kidney failure; consider ureteric stent if obstructing 4
• Persistent symptoms with known stones: Assess for stone migration, passage, or complications (infection, perinephric abscess, urinoma) 1

Common Pitfalls

• Assuming all flank pain is renal: Thoracic disc herniation can mimic urinary disorders 7
• Delaying imaging in cauda equina: Urinary retention has 90% sensitivity; without it, probability drops to 1 in 10,000 1
• Routine imaging for nonspecific low back pain: Does not improve outcomes and increases costs 1
• Missing cancer in older patients: Age >50 alone only increases cancer probability to 1.2%, but history of cancer increases it to 9% 1
• Overreliance on straight-leg raise: High sensitivity (91%) but poor specificity (26%) for herniated disc; crossed straight-leg raise more specific (88%) but less sensitive (29%) 1