What are the typical symptoms of an L5‑S1 disc bulge compressing the cauda equina?

Symptoms of L5-S1 Disc Bulge Compressing the Cauda Equina

An L5-S1 disc bulge causing cauda equina compression presents with bilateral leg symptoms (pain, numbness, or weakness in both legs), new bladder difficulties (hesitancy, poor stream, urgency), and perineal sensory changes—these "red flag" symptoms demand immediate emergency MRI and neurosurgical consultation before progression to irreversible urinary retention, complete saddle anesthesia, and fecal incontinence. 1

Early Warning Signs ("Red Flags") Requiring Immediate Action

The critical early symptoms that should trigger emergency evaluation include:

• Bilateral radiculopathy: Pain, numbness, tingling, or weakness radiating down both legs below the knee, distinguishing this from typical unilateral sciatica 1, 2
• New bladder symptoms with preserved control: Hesitancy, poor urinary stream, urgency, or difficulty initiating urination—even when the patient can still void voluntarily 1
• Perineal sensory changes: Subjective numbness, tingling, or "pins and needles" sensation in the saddle area (perineum, buttocks, inner thighs, genitals) 1, 3
• Progressive lower extremity motor weakness: Worsening weakness in both legs, affecting foot dorsiflexion (L5), plantarflexion (S1), or knee extension (L4) 1, 2
• Severe low back pain overshadowing leg pain: Intense axial back pain that dominates the clinical picture, which should heighten suspicion 3, 1

These symptoms typically develop gradually over weeks to months with L5-S1 disc pathology, making early recognition critical before irreversible damage occurs. 1

Late Signs Indicating Irreversible Damage ("White Flags")

Do not wait for these symptoms to initiate referral—they represent established, often permanent neurological injury: 1

• Painless urinary retention: Inability to void with a distended bladder but no discomfort; this has 90% sensitivity for established cauda equina syndrome 2, 1
• Complete saddle anesthesia: Total loss of sensation in the perineal region rather than partial sensory changes 1, 4
• Fecal incontinence: Loss of bowel control 1, 3
• Patulous (lax) anus: Loss of anal sphincter tone on examination 1
• Frank paraplegia: Complete bilateral lower extremity paralysis 3, 4

Patients presenting with these late signs have only 48-93% chance of any improvement even with emergency surgery, and many require lifelong intermittent catheterization, manual fecal evacuation, and experience permanent loss of sexual function. 1

Clinical Staging and Prognosis

Understanding the stage at presentation determines expected outcomes:

• Suspected CES (CESS): Bilateral radiculopathy without objective bladder/bowel dysfunction—early treatment at this stage prevents progression and preserves normal function 1
• Incomplete CES (CESI): New bladder symptoms with preserved control plus perineal sensory loss—early decompression yields normal or socially normal long-term bladder, bowel, and sexual function 1
• CES with Retention (CESR): Painless urinary retention, complete perineal anesthesia, or fecal incontinence—variable recovery with high risk of permanent disability despite surgery 1

Physical Examination Findings

Specific examination maneuvers help confirm nerve root involvement at L5-S1:

• Straight-leg-raise test: Reproduction of radicular leg pain between 30-70 degrees of leg elevation has 91% sensitivity for disc herniation 2, 5
• Crossed straight-leg-raise: More specific (88%) but less sensitive (29%) when raising the opposite leg reproduces the patient's symptoms 2, 5
• Motor testing: Assess foot plantarflexion and ankle reflexes (S1 nerve root), great toe and foot dorsiflexion strength (L5 nerve root) 2, 5
• Perineal sensation: Carefully test light touch in the saddle distribution, though subtle impairment is easily missed 1
• Rectal examination: Assess voluntary rectal tone and bulbocavernosus reflex, though interobserver reliability is low among inexperienced clinicians 1

Common Pitfalls to Avoid

• Never wait for complete urinary retention before referral—this represents a late sign of irreversible damage 1
• Do not catheterize before assessing post-void residual volume, as this obscures whether the patient is in the incomplete or complete stage 1
• Do not rely on unilateral sciatica to rule out cauda equina syndrome—early compression may present with predominantly unilateral symptoms before progressing to bilateral involvement 6, 1
• Do not dismiss subtle perineal sensory changes—subjective numbness reported by the patient is significant even when objective examination seems equivocal 1

Immediate Diagnostic Approach

• Emergency MRI of the lumbar spine without IV contrast is the gold standard (96% sensitivity, 94% specificity) and must be performed immediately in all suspected cases 1
• CT scan alone is inadequate with only 6% sensitivity for neural compression and cannot adequately visualize the cauda equina nerve roots or epidural space 1
• More than 90% of symptomatic lumbar disc herniations causing radiculopathy occur at L4/L5 and L5/S1 levels 2, 5
• L5-S1 disc herniation accounts for approximately 45% of all cauda equina syndrome cases 7

The key principle: bilateral symptoms, new bladder changes, or perineal sensory loss from an L5-S1 disc bulge constitute a surgical emergency requiring MRI within hours, not days, to prevent permanent neurological disability. 1, 7