Acute Low Back Pain and Lumbar Radiculopathy
Mechanical low back pain with or without nerve root impingement; most cases improve with conservative care.
Also known as: low back pain, LBP, lumbar radiculopathy, sciatica, disc herniation, lumbar disc
Overview
Acute low back pain (LBP) is back pain of <6 weeks duration without serious underlying pathology. Lumbar radiculopathy is pain, weakness, numbness, or paresthesias in a dermatomal distribution from compression or inflammation of a lumbosacral nerve root, most commonly L4-L5 or L5-S1 (sciatica).
Epidemiology
Lifetime prevalence of LBP ~80%. Most acute episodes resolve within 4-6 weeks. Lumbar disc herniation is most common in adults aged 30-50.
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Risk factors
- Heavy lifting, twisting, prolonged sitting or driving
- Obesity, deconditioning
- Smoking
- Depression, anxiety, somatization, low job satisfaction
- Prior episode of LBP
- Pregnancy
- Older age (degenerative disc and stenosis)
Pathophysiology
Most acute LBP is mechanical — muscle/ligament strain, facet joint, sacroiliac joint, or annular tear. Disc herniation occurs when nucleus pulposus extrudes through a tear in the annulus fibrosus, compressing an adjacent nerve root. Chemical irritation from inflammatory mediators released by the disc contributes to radicular pain.
Clinical presentation
Symptoms
- Mechanical LBP: dull aching, often after a triggering event; worse with movement, better with rest
- Lumbar radiculopathy: sharp, lancinating leg pain in a dermatomal distribution, often worse than back pain itself
- Worse with sitting, bending, coughing, sneezing, Valsalva
- Numbness, paresthesias, weakness in specific distributions
Signs / physical exam
- Paraspinal muscle tenderness, reduced range of motion
- Positive straight-leg raise (radicular pain reproduced with elevation 30-70°)
- Crossed straight-leg raise (less sensitive, more specific)
- Dermatomal sensory loss and myotomal weakness:
- • L4: medial leg/foot, knee extension, patellar reflex
- • L5: dorsum of foot, big toe extension, dorsiflexion
- • S1: lateral foot, plantar flexion, ankle reflex
- Red flag findings: saddle anesthesia, decreased anal tone, urinary retention or incontinence (cauda equina)
Differential diagnosis
- Mechanical LBP / muscle strain — No radicular pattern, normal neurologic exam, improves with conservative care
- Lumbar spinal stenosis — Older adult, neurogenic claudication, relieved by flexion (leaning on shopping cart)
- Spondylolisthesis — Anterior slip of vertebra; back pain ± radicular features; oblique radiograph for pars defects
- Compression fracture — Sudden pain after minor trauma; osteoporosis, steroid use, malignancy; focal tenderness
- Vertebral osteomyelitis / epidural abscess — Fever, IVDU, immunosuppression, elevated ESR/CRP; MRI
- Malignancy (mets, myeloma) — Age >50, history of cancer, weight loss, night pain, focal tenderness
- Cauda equina syndrome — Saddle anesthesia, urinary retention or incontinence, bilateral leg weakness — surgical emergency
- Inflammatory back pain (axSpA) — Age <45, morning stiffness, improvement with exercise
- Abdominal aortic aneurysm — Older smoker, pulsatile abdominal mass, severe back pain; ultrasound/CT
- Renal colic / pyelonephritis — Flank pain, hematuria, urinary symptoms
- Hip pathology (OA, AVN) — Groin pain reproduced by hip motion; FABER positive
Diagnostic workup
Diagnostic criteria
Clinical — based on history, exam, and exclusion of red flags.
Labs
- Routine labs not needed in acute LBP without red flags
- CBC, ESR, CRP if infection or malignancy suspected
- PSA, SPEP/UPEP if malignancy suspected
Imaging
- NO imaging in the first 4-6 weeks unless red flags or progressive neurologic deficit (ACR Choosing Wisely)
- MRI lumbar spine — best for disc herniation, stenosis, infection, malignancy, cauda equina
- CT — if MRI contraindicated; better for bone detail
- Plain radiographs — limited utility but used to assess alignment, spondylolisthesis, fracture, malignancy screen
Diagnostic algorithm
| Nerve Root | Sensory | Motor | Reflex |
|---|---|---|---|
| L4 | Medial leg/foot | Knee extension (quadriceps) | Patellar |
| L5 | Dorsum of foot, big toe | Big toe extension, ankle dorsiflexion | None reliable |
| S1 | Lateral foot, sole | Ankle plantar flexion (gastroc-soleus) | Achilles |
| Cauda equina | Saddle anesthesia (bilateral) | Bilateral lower extremity weakness | Decreased rectal tone; urinary retention |
Treatment
First-line
- Reassurance and education that most acute LBP resolves in 4-6 weeks
- Stay active — bed rest worsens outcomes
- Non-pharmacologic first: heat, massage, spinal manipulation, acupuncture
- NSAIDs — ibuprofen, naproxen, meloxicam — first-line pharmacotherapy
- Acetaminophen — not effective for acute LBP vs placebo (PACE trial; ACP 2017); NSAIDs are the preferred first-line analgesic
- Skeletal muscle relaxants — cyclobenzaprine, methocarbamol, tizanidine — short course for muscle spasm
- Avoid opioids except for severe pain refractory to other measures — limit to brief course
Complications
- Persistent or recurrent LBP
- Chronic radiculopathy with neurologic deficit
- Cauda equina syndrome with permanent bowel/bladder dysfunction if not decompressed urgently
- Disability, work loss, opioid dependence
- Postoperative failed back syndrome
PANCE pearls
- Imaging in the first 4-6 weeks of LBP without red flags often shows incidental findings that lead to unnecessary intervention.
- Straight-leg raise has reasonable sensitivity but moderate specificity; crossed SLR is highly specific for disc herniation.
- Cauda equina is a true emergency — saddle anesthesia and new bladder dysfunction warrant immediate MRI and surgical consult.
- Most lumbar disc herniations resolve with conservative care; surgery improves short-term pain but long-term outcomes are similar.
- Bed rest is harmful — encourage early return to activity within pain tolerance.
References
- ACP 2017 — Noninvasive Treatments for Acute, Subacute, and Chronic Low Back Pain: ACP Clinical Practice Guideline (Qaseem et al., Ann Intern Med 2017)
- NASS 2014 — Diagnosis and Treatment of Lumbar Disc Herniation with Radiculopathy: NASS Evidence-Based Clinical Guidelines (Kreiner et al., Spine J 2014)
- ACR Appropriateness — ACR Appropriateness Criteria — Low Back Pain (Patel et al., J Am Coll Radiol 2016)
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