Differential Diagnoses for Lumbar Sprain
When evaluating a patient presenting with what appears to be a lumbar sprain, you must systematically rule out serious pathology using red flag criteria before accepting a benign musculoskeletal diagnosis. 1, 2
Critical "Red Flag" Conditions to Exclude First
The following serious conditions must be actively ruled out through targeted history and examination, as they require urgent intervention and dramatically affect morbidity and mortality:
Cauda Equina Syndrome (CES)
- Urinary retention (90% sensitivity) - most critical finding 1
- Fecal incontinence
- Saddle anesthesia/perianal numbness
- Bilateral leg weakness or numbness
- Without urinary retention, probability drops to 1 in 10,000 1
- Most commonly caused by L4-L5 or L5-S1 disc herniation 2
Malignancy
Look for these specific risk factors that increase probability:
- History of cancer increases probability from 0.7% to 9% (positive likelihood ratio 14.7) 1
- Age >50 years (positive likelihood ratio 2.7)
- Unexplained weight loss (positive likelihood ratio 2.7)
- Failure to improve after 1 month (positive likelihood ratio 3.0)
- Any single non-cancer risk factor only raises probability to ~1.2% 1
Vertebral Infection
- Fever
- Intravenous drug use
- Recent infection 1
Vertebral Compression Fracture
- Older age
- History of osteoporosis
- Corticosteroid use 1
Ankylosing Spondylitis
- Younger age
- Morning stiffness improving with exercise
- Alternating buttock pain
- Awakening due to back pain during second part of night only 1
Vascular Emergencies
- Abdominal aortic aneurysm
- Consider in older patients with cardiovascular risk factors 1
Systemic Illnesses
- Endocarditis
- Viral syndromes 1
Musculoskeletal Differential Diagnoses
Once red flags are excluded, consider these common intrinsic spinal causes:
Herniated Disc with Radiculopathy
- >90% occur at L4/L5 and L5/S1 levels 1
- Straight-leg raise test: 91% sensitivity but only 26% specificity 1
- Crossed straight-leg raise: 88% specificity but only 29% sensitivity 1
- Assess specific nerve root patterns:
- L4: knee strength and reflexes
- L5: great toe and foot dorsiflexion strength
- S1: foot plantarflexion and ankle reflexes 1
Lumbar Spinal Stenosis
- Age >65 years (positive likelihood ratio 2.5) 1
- Pseudoclaudication (positive likelihood ratio 1.2)
- Radiating leg pain (positive likelihood ratio 2.2)
- Symptoms changing on downhill treadmill testing (positive likelihood ratio 3.1) 1
- Pain relieved by sitting (variable predictive value)
Facet Joint Syndrome
- Localized paraspinal tenderness
- Pain with extension and rotation 3
Sacroiliac Joint Dysfunction
- Unilateral buttock pain
- Pain with specific provocative maneuvers 4
Myofascial Pain/Muscle Strain
- Trigger points identifiable on examination
- Localized muscle tenderness 5
Spondylolysis/Spondylolisthesis
- More common in younger athletes
- Pain with hyperextension 2
Referred Pain Sources (Extravertebral)
These conditions present as low back pain but originate from distant structures:
- Renal: Kidney stones, pyelonephritis, renal infarction
- Pancreatic: Pancreatitis, pancreatic cancer
- Gastrointestinal: Peptic ulcer disease, diverticulitis, colon cancer
- Gynecologic: Endometriosis, ovarian cysts, pelvic inflammatory disease
- Vascular: Aortic aneurysm, aortic dissection 3, 6
Critical Clinical Approach
Psychosocial factors are stronger predictors of outcomes than physical findings or pain severity 1. Assess for:
- Depression
- Job dissatisfaction
- Pending litigation
- Fear-avoidance behaviors
These factors identify patients at risk for delayed recovery and chronic disability 1.
Common Pitfalls to Avoid
Do not routinely image acute low back pain (<4 weeks) without red flags - imaging provides no clinical benefit and may reveal incidental findings that worsen patient anxiety 2
Disc abnormalities on imaging are common in asymptomatic patients - 29% of 20-year-olds and 43% of 80-year-olds have disc protrusions without symptoms 2
Early imaging increases healthcare utilization without improving outcomes - patients receiving MRI within 6 weeks had increased likelihood of injections, surgery, and disability compensation 2
Most disc herniations show reabsorption by 8 weeks - even with herniation present, conservative management is typically appropriate initially 2