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A 45-year-old male presents with low back pain radiating to the left leg for 3 months. The pain worsens on coughing and bending forward. He has numbness along the lateral leg and weakness in dorsiflexion of the foot. Straight leg raise test is positive at 40" MRI shows L4-L5 disc prolapse. DIAGNOSIS Lumbar Disc Prolapse L4/L5 (L5 Nerve Root Compression) SUB-QUESTIONS A. What is the most likely diagnosis? (2 marks) B. Which nerve root is involved? (2 marks) C. Mention two indications for surgical intervention: (2 marks)

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Finding Sources

A. Most Likely Diagnosis (2 marks)

Prolapsed Intervertebral Disc (PIVD) at L4-L5 level with left-sided L5 nerve root compression (sciatica)
The clinical picture is classic:
  • Low back pain radiating down the leg for 3 months (chronic sciatica)
  • Aggravation on coughing/straining and forward bending (raises intrathecal/intradiscal pressure, stretching the compressed root)
  • Positive Straight Leg Raise (SLR) test at 40° (Lasègue's sign - confirms nerve root tension/irritation; a positive SLR below 60-70° is significant)
  • MRI confirming L4-L5 disc prolapse
This is corroborated by standard references: "In the lumbar region, the most common disc prolapse is at the L4-L5 or L5-S1 level, resulting in signs and symptoms referable to the L5 or S1 roots" - Localization in Clinical Neurology, 8e.

B. Nerve Root Involved (2 marks)

Left L5 nerve root.
Reasoning: At the L4-L5 disc level, a posterolateral prolapse typically compresses the traversing nerve root (L5), not the exiting L4 root, because the L4 root has already left the canal above this level while the L5 root is still crossing behind the disc on its way to exit at the L5-S1 foramen.
This fits the exam findings perfectly:
  • Sensory: Numbness over the lateral aspect of the leg and dorsum of the foot (L5 dermatome)
  • Motor: Weakness of ankle/great toe dorsiflexion - tibialis anterior and extensor hallucis longus are the key L5 myotome muscles (a foot-drop pattern)
  • (Contrast with S1 lesion, which would give calf pain/numbness, weak plantar flexion/eversion, and a diminished ankle jerk)

C. Indications for Surgical Intervention (2 marks - any two)

  1. Cauda equina syndrome - bladder/bowel incontinence or retention, saddle anesthesia, bilateral leg weakness (surgical emergency, needs decompression within 24-48 hours)
  2. Progressive or severe neurological deficit - worsening motor weakness (e.g., progressive foot drop) or significant/progressive muscle weakness despite conservative treatment
  3. Failure of adequate conservative management - persistent disabling pain/sciatica for 6-12 weeks despite rest, analgesics/NSAIDs, physiotherapy, and epidural steroid injections
  4. Intractable pain significantly affecting quality of life and daily activities, unresponsive to conservative measures
(This patient, having had symptoms for 3 months with objective motor weakness in dorsiflexion, already meets criteria for surgical evaluation - i.e., both failed conservative therapy and a neurological deficit.)
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