Low Back Pain Algorithm and Differential Diagnosis

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General Red Flags for Low Back Pain

General Approach

  • Begin work-up by ruling out emergent/urgent conditions and evaluating/charting the absence of red flags that can signal the presence of an emergent condition
  • Then consider other visceral causes of low back pain
  • If no red flags are present and patient does not need further work-up, then the likely default diagnosis is benign mechanical (lumbar strain) LBP


  • <20 years old
    • Increased incidence of congenital, developmental, bony abnormalities, and malignancy
  • >50 years old
    • Increased incidence of serious causes (AAA, vertebral fracture, pancreatitis…)

Duration of Symptoms

Atypical pain features

  • Awaken from sleep
  • Intractable pain
    • Consider: infection, tumor, fracture, nerve impingement, or non-musculoskeletal causes
Low Back Pain Algorithm
Low Back Pain Algorithm

Emergent Conditions of Low Back Pain

1. Abdominal Aortic Aneurysm (AAA) / Aortic Dissection

Abdominal Aortic Aneurysm (AAA)

  • Presentation
    • Usually asymptomatic until rupture
    • Acute epigastric and back pain
    • Wide pulsatile abdominal mass
    • Renal colic mimic (back pain, hematuria)
  • AAA Risk factors (age, male, smoking, CAD/PVD, Family History)
Abdominal Aortic Aneurysm - Clinical Findings and Complications
Abdominal Aortic Aneurysm – Clinical Findings and Complications

Aortic Dissection

  • Presentation
    • Sudden-onset, severe, “tearing” pain
    • Pulse/neuro deficit
    • New Aortic Insifficiency murmur
    • Limb ischemia
  • Risk factors: HTN (Hypertension), Marfan’s, vasculitis, pregnancy, coarctation, bicuspid aortic valve, trauma, cocaine/meth

2. Epidural Compression

Causes of Epidural Compression

  • Spinal cord compression,
  • Conus medullaris syndrome,
  • Cauda Equina syndrome

Clinical Presentation of Epidural Compression

  • History of cancer ?
  • Multiple myotomes/dermatomes may be involved
  • Focal Neurologic deficit:
    • Bilateral Lower Extremity weakness, sciatica change, gait disturbance
    • Bowel/bladder incontinence caused by urinary retention (PVR (post-void residual urine volume) >100-200ml)
    • Decreased rectal tone
    • Motor > Sensory loss
    • Sensory loss: saddle anesthesia, sensory level
  • Age (JAMA 1992;268;760-5)
    • Age > 50 or history of Cancer or unexplained weight loss or failure of conservative therapy → Sens 100% for detecting metastasis to spine

Work-up for Epidural Compression

  • Overflow incontinence
    • Cause (J Bone Joint Surg Am 1986;68:386)
      • Urinary retention (sensitivity 90%, specificity 95% for epidural compression)
    • Abnormal PVR (post-void residual urine volume)
      • Absence of large PVR (>100ml) has NPV (Negative predictive value) 99.99%
      • In absence of significant neurologic deficit → normal PVR rules out compression
    • Post-void US: Volume = Length x Width x Height x (0.52)
    • Anal sphincter tone diminished in 60-80%
    • Saddle anesthesia has sensitivity 75%
  • MRI
    • Diagnose site of compression

Special Case: Patient with history of Cancer (Emerg Med Clin N Am 2010;28:811)

  • Group I: New/progressive neurologic symptoms
    • Steroids (Dexamethasone 10mg IV)
    • Xrays, emergent MRI
  • Group II: Stable neurologic symptoms
  • Group III: No neurologic signs/symptoms
    • Conservative therapy
    • Xrays, outpatient MRI

Treatment of Epidural Compression

  • Emergent Neurosurgical Consult
  • Steroids/Radiation if due to metastasis

3. Spinal Epidural Abscess (SEA)

Other infectious causes of low back pain

  • Epidural abscess
  • Osteomyelitis
  • Discitis
  • Transverse Myelitis

Clinical Presentation of Spinal Epidural Abscess

Spinal Epidural Abscess (SEA) Triad

Spine pain
Neurologic deficit

  • Classic Triad (Fever, Spine pain, neuro deficit)
    • Triad present in only 13% patients with SEA and is usually a late finding
    • Must consider risk factor screening for rulling out epidural abscess. (J Emerg Med 2004;26:285-91)
  • Progression of symptoms:
    • Back pain → Radiculopathy → Sensory changes/motor weakness → Bowel-bladder dysfunction → Paralysis
  • Risk Factors:
    • Intravenous drug abuse
    • immunocompromised
    • alcohol abuse
    • spine procedure
    • distant infection
    • Diabetes Mellitus
    • Chronic Kidney Failure (CKD)
    • Cancer
    • indwelling catheter
    • spine fracture
  • Risk factor screening sensitivity 98%, for one or more risk factors

Work-up for Spinal Epidural Abscess

  • ESR (Erythrocyte sedimentation rate) (J Neurosurg Spine 2011;14:765-770)
    • Used as screening test for value of >20mm/h (sens 100%)
    • Useful as screening tool for ED patients with spine pain, risk factor for Spinal Epidural Abscess and no neurologic deficits
  • Emergent MRI

Treatment of Spinal Epidural Abscess

  • Broad spectrum antibiotics (Staph/Strep/gm neg)
  • Emergent Neurosurgical consultation

4. Vertebral Fracture

Clinical Presentation of Vertebral Fracture

  • Usually elderly with osteoporosis
  • Trauma
  • Point Vertebral Tenderness
  • Steroid use
    • A person with Lower Back Pain on long-term steroids is considered to have a compression fracture until proven otherwise (Spec 99%)

Work-up for Vertebral Fracture

• Xrays / CT Spine

Visceral Causes of Low Back Pain

1. UTI / Pyelonephritis


  • Uncomplicated UTI: young, healthy, non-pregnant women with structurally and functionally normal urinary tracts
  • Complicated UTI: UTI associated with an underlying condition that increases the risk of failing therapy
  • Complicated pyelonephritis: progression of upper UTI to emphysematous pyelonephritis, renal corticomedullary abscess, perinephric abscess, or papillary necrosis
Pathogenesis of Urinary Tract Infection (UTI)
Pathogenesis of Urinary Tract Infection (UTI)

Risk Factors for Complicated UTI

□ Pregnancy
□ Diabetes
□ Male gender
□ Immunosuppression (AIDS, chemotherapy…)
□ Functional GentioUrinay abnormality (catheter, neurogenic bladder…)
□ Structural GU abnormality (stones, fistula, PCKD, transpant…)

Risk Factors for UTIs (Urinary Tract Infections)
Risk Factors for UTIs (Urinary Tract Infections)

Clinical Presentation

  • Cystitis
    • Urinary frequency and urgency, dysuria, and hematuria
    • Suprapubic pain, low back pain
    • New or increased incontinence in older patients or Altered Mental Status / Delirium
  • Pyelonephritis
    • Flank or abdominal pain, CVA (costovertebral angle) tenderness on exam
    • Fever/chills, Nausesa / Vomitus
    • Complicated Pyelonephritis (Sepsis, Renal failure)


  • Urine Dipstick / Urine Analysis (UA)
    • Either nitrite OR leukocyte esterase (LE) positive: 75% sensitive, 82% specific
    • Nitrite AND leukocyte esterase positive: 35-84% sensitive, 98-100% specific
    • Nitrite alone (95-98%) more specific than leukocyte esterase alone (59-96%) but S. saprophyticus, pseudomonas, and enterococci do not reduce nitrate
    • False positive LE (leukocyte esterase) with vaginitis or cervicitis
    • Pyuria and bacteruria may be absent if obstruction of the collecting system or ureters is present
  • Urine Microscopy
    • White blood cell casts are diagnostic of upper urinary tract infection
  • Urine culture
    • Helpful in guiding antibiotic therapy in pyelonephritis or failed antibiotic treatment
    • Positive: single organism isolated with ≥ 100,000 CFU
  • Imaging
    • Not routinely necessary
    • CT abdomen/pelvis with/without IV contrast consider to/if :
      • rule out infected/obstructed ureteral stone
      • rule out pyelonephritis complication (abscess…):
        • Consider if failure of response to therapy in 48-72 hours
      • Recurrence of symptoms within a few weeks of therapy
      • Suspicion for obstruction, gas, hemorrhage, masses
    • Ultrasound:
      • Rule out hydronephrosis / obstruction / stone
Proposed algorithm for evaluating women with symptoms of acute urinary tract infection (UTI)
Proposed algorithm for evaluating women with symptoms of acute urinary tract infection (UTI)


  • Antibiotics
    • Base antibiotic selection on previous culture data, local resistance patterns, patients history and medical problems
  • Adjunctive pain control option: Phenazopyridine PO TID (urinary analgesic).
  • See Current Guidelines (Clinical Infectious Diseases 2011;52(5):e103)


  • Pyonephrosis
    • Infection + obstruction (pus under pressure)
    • Pyelonephritis with an obstructing stone, mass, or other obstruction
    • Therapy: emergent urology/interventional radiology consult for percutaneous nephrostomy tube or stenting
  • Renal abscess
    • Diagnosis: CT with IV contrast; can be visualized on Ultrasound
    • Therapy: Resuscitation, antibiotics, percutaneous drainage (depending on size and response to antibiotics)
  • Emphysematous UTI
    • Definition: necrotizing infection with gas formation in bladder (cystitis), renal pelvis (pyelitis) or kidney parenchyma (pyelonephritis)
    • High mortality (20% to 40%) even with treatment
    • 95% of cases occur in patients with DM
    • Major risk factor is infected obstructing stone
  • Papillary necrosis
    • Definition: coagulative necrosis of the renal medullary pyramids and papillae


  • Outpatient therapy appropriate if:
    • Uncomplicated pyelonephritis
    • Normal vitals, normal renal function, no urinary obstruction
    • Pain control and hydration status adequate
    • Able to tolerate Oral medications

2. Renal Colic

Clinical Presentation of Renal Colic

  • Renal colic
    • Mechanism of Action: obstruction of urinary tract → ↑ pressures → renal capsular distention (visceral pain/N/V) → ↑ peristalsis of ureter (colicky pain)
    • Unilateral flank pain → radiating to groin
    • Migration of pain (depending on location of stone):
    • Colic pain: intermittent, waxes/wanes, patient writhing, unable to sit still
  • Urinary symptoms: urgency, frequency, dysuria, gross hematuria
  • Nausea/vomiting
  • Physical Exam : CVA (costovertebral angle) tenderness or lower abdominal tenderness

Diagnosing Renal Colic

  • Urinalysis
    • Microscopic hematuria only 85% sensitive for urolithiasis
    • Use to rule-out infection/UTI and infected stone
    • UA negative?: Patient may still have urine infection proximal to obstructing stone
  • KUB (kidney, ureter, and bladder X-ray)
    • 85-90% of stones are radioopaque (calcium, struvite, cystine) but KUB only 40-62% sensitive and 60-67% specific
    • Little diagnostic utility; consider in patient with known history of radiopaque stones and typical presentation
  • Ultrasound
    • Ureteral calculi
      • Sensitivity 45% and specificity 94%
      • More likely to see larger stones (>4mm), at the UVJ (ureterovesical junction), or proximal near the renal pelvis.
    • Hydronephrosis
      • Sensitivity 85-90% and specificity 90-100%
      • Not visualize stone itself but can demonstrate obstructive sequelae
      • Presence/absence of hydronephrosis is neither diagnostic nor prognostic
    • Preferred initial test in pregnancy, children → no radiation
    • Use to evaluate abdomen/pelvis for alternative diagnoses (gallstones, appy etc…)
  • CT (Non-contrast):
    • Study of choice to evaluate urolithiasis
    • Indications:
      • 1st time diagnosis of urolithiasis
      • Atypical presentation
      • Rule out infection
      • Not improving with conservative treatment
    • Sensitivity 96-98% and specificity ~100%
    • Useful in prognosis (size/location of stone, obstruction/hydronephrosis, perinephric stranding)
  • No imaging ?:
    • Pt with known kidney stone, typical presentation, well appearing, no risks for complications and good follow/up
    • May treat empirically (pain control, hydration)

Treatment of Renal Colic

  • Conservative treatment
    • Pain control, hydration, expectant stone passage.
  • NSAIDs
    • Inhibits prostaglandin-mediated process in urolithiasis
    • As effective as opioids and fewer side effects of nausea and vomiting
    • Ketorolac IV or Ketorolac + Opiate combination
  • Opiates
    • In addition to NSAID or if contraindications to NSAID
  • Hydration & Diuresis
    • No evidence that increased hydration or forced diuresis improves pain scores or rate of passage ⇒ Use: replete volume in dehydrated patients or those with elevated creatinine only
  • Medical Expulsion Therapy:
    • CCBs (e.g nifedipine) or α-antagonists (e.g. tamsulosin)
    • Mechanism of Action: relax ureteral smooth muscle → allow passage of stone
    • Conclusion: Trial of tamsulosin (0.4 mg qd x4 weeks) in stones <10mm is reasonable
  • Emergent urology consult
    • Urosepsis, obstruction with proximal infection, AKI, anuria, intractable pain/vomiting, stones >10mm
  • Renal Stents
    • Use:
      • Facilitate drainage of upper urinary tract and relieve obstruction
      • Temporizing while await stone passage or definitive urological procedure.
    • Complications: pain, hematuria, urgency and frequency (more common), upward migration, infection, sepsis (rare)
  • Infected kidney stone
    • Treatment: decompression, emergently by urology or IR
    • Admission, hydration, IV antibiotics
    • UTI + non-obstructing stone: if well appearing, outpatient antibiotics, urology follow-up
Size of stoneRate of passage
1 mm87 %
2-4 mm76 %
5-7 mm60 %
7-9 mm48 %
>9 mm25 %


  • Admit
    • Obstructing stone with a proximal infection, urosepsis, acute renal failure, anuria, or intractable pain, nausea, or vomiting
    • Urology consult
  • Discharge Home
    • Stable, tolerating po, pain controlled, nausea/vomiting controlled, outpatient urology follow-up
    • Outpatient Urology follow-up:
      • Stone >10mm, failure to pass stone after conservative treatment, pain not controlled

Journal Club: Tamsulosin in ureteral stones

RCT (Arch Intern Med 2010;170:2021)

  • Study: multicenter, placebo-controlled, randomized, double-blind study of tamsulosin vs placebo (good)
  • No difference in expulsion delay within 42 days; (P = .30)
  • No difference in surgical procedure or other secondary end points between groups
  • Conclusion: “Tamsulosin did not accelerate the expulsion of distal ureteral stones in patients with ureteral colic”

Systematic review (Ann Emerg Med. 2007;50:552)

  • Previous review suggested increase stone passage rate and decreased time to stone passage with tamsulosin
  • Critique: Review had poor quality, unblinded studies, poor follow up

Mechanical Low Back Pain

1. Sciatica (ischialgia)


  • Peripheral radiculopathy caused by compression of nerve root, usually caused by disc herniation or spinal stenosis

Clinical Presentation of Sciatica

  • Back pain + neuropathy (paresthesia, sensory loss) down one leg
  • Unilateral symptoms that extend distal to knee
  • Sensory > Motor
  • Single myo/dermatome involved
  • SLR (Straight leg raise) called Lasègue test or Lazarević’s sign
    • Pain when the straight leg is raised to an angle of between 30 and 70 degrees
    • Pain must extend below knee
    • Sensitivity 91%, Specificity 26% (Spine 25 (9): 1140–7)
  • Crossed SLR: Raising the opposite leg causes pain on affected side (sensitivity 29%, specificity 88%)

Treatment of Sciatica

  • 90% of acute sciatica responds to conservative treatment
  • Conservative management: Tylenol / NSAIDS / continue daily activities
  • Treat similar to lumbar strain except consider Xrays to rule out other causes of nerve compression (tumor, fracture, spondylolisthesis, infection…)
  • Emergent/Urgent Surgery
    • Significant motor deficit (foot drop, unable to ambulate)
    • Intractable pain
  • Indications for outpatient surgery
    • Definite herniation on imaging study +
    • Corresponding pain syndrome +
    • Corresponding neurologic deficit +
    • No response to 4-6 weeks conservative treatment

2. Lumbar Strain


  • Diagnosis of exclusion
  • No further work-up needed


• Activity as tolerated
• Analgesics / Muscle relaxants
• Continuing normal daily activities as tolerated leads to more rapid recovery than either bed rest or back immobilizing exercises (NEJM 1995;332(6):351-5)


  1. https://pubmed.ncbi.nlm.nih.gov/20971393/
  2. https://pubmed.ncbi.nlm.nih.gov/10584107/
  3. https://pubmed.ncbi.nlm.nih.gov/1386391/
  4. https://pubmed.ncbi.nlm.nih.gov/2936744/
  5. https://pubmed.ncbi.nlm.nih.gov/15028325/
  6. https://pubmed.ncbi.nlm.nih.gov/21417700/
  7. https://pubmed.ncbi.nlm.nih.gov/21782073/
  8. https://pubmed.ncbi.nlm.nih.gov/21292654/
  9. https://www.ncbi.nlm.nih.gov/books/NBK109618/
  10. https://pubmed.ncbi.nlm.nih.gov/17681643/
  11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1895638/
  12. https://www.nejm.org/doi/full/10.1056/nejm199502093320602