Musculoskeletal · PANCE / PANRE

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

Lumbosacral radiculopathy localization — pattern-matching at the bedside.

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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