PLAB 2 Cauda Equina Station: Red Flags, Emergency MRI & Free Practice

Hold these differentials in your head

Bracket the deadly causes first. If you fail to consider any of these in your reasoning out loud, the clinical-management domain will suffer.

• Cauda equina syndrome
  Compression of the lumbosacral nerve roots, usually by a large central disc prolapse. Saddle anaesthesia, bladder or bowel dysfunction, bilateral sciatica and lower-limb weakness. The emergency the station is testing.
• Mechanical or muscular lower back pain
  Pain related to movement and posture with no neurological deficit and no red flags. The common benign cause - but a diagnosis of exclusion once cauda equina is ruled out.
• Lumbar disc prolapse with unilateral sciatica
  Radicular leg pain in one dermatome without saddle or sphincter involvement. Managed conservatively in the first instance - distinct from cauda equina.
• Spinal metastasis or malignant cord compression
  Back pain with weight loss, night pain, a history of cancer or age over 50. Also a spinal emergency - keep it on the differential alongside cauda equina.
• Spinal infection (discitis or epidural abscess)
  Back pain with fever, raised inflammatory markers, intravenous drug use or immunosuppression. Can cause cord or cauda compression and needs urgent imaging.
• Vertebral fracture
  Sudden pain after trauma, or atraumatic in osteoporosis or steroid use. Consider in the older or at-risk patient.

Step-by-step approach

This is the structure that scores. You do not need to follow it verbatim, but every numbered block below maps to a cluster of marks in the rubric.

1. 1. Open the consultation

   Greet and set the tone, then move efficiently - this is time-critical.

   • Wash hands, greet, introduce yourself with name and grade.
   • Confirm name and date of birth.
   • Acknowledge the pain and explain you need to ask some specific questions.

2. 2. Characterise the back pain (SOCRATES)

   Cover the pain, but the red-flag screen below carries the marks.

   • Site, onset, character, radiation into the legs.
   • Time course, severity, exacerbating and relieving factors.
   • Any preceding trauma or heavy lifting.

3. 3. Screen the cauda equina red flags - the core of the station

   Ask each one explicitly. Vague questioning leaves the marks on the table.

   • Saddle anaesthesia - numbness or altered sensation around the back passage, genitals or inner thighs ("any numbness when you wipe?").
   • Bladder dysfunction - difficulty passing urine, retention, or incontinence; loss of the sensation of needing to go.
   • Bowel dysfunction - incontinence or loss of control.
   • Bilateral leg symptoms - pain, weakness or numbness in both legs.
   • Sexual dysfunction - new loss of sensation.
   • Difficulty walking or legs giving way.

4. 4. Screen other back-pain red flags

   Rule the dangerous mimics in or out.

   • Weight loss, night pain, history of cancer (metastasis).
   • Fever, intravenous drug use, immunosuppression (infection).
   • Significant trauma; age under 20 or over 50 with new pain.
   • Steroid use or known osteoporosis (fracture).

5. 5. Complete the history

   Round out the background quickly.

   • Past medical history, medications, allergies.
   • Social history and impact on function.
   • Ideas, concerns and expectations - acknowledge the fear without false reassurance.

6. 6. Request the targeted examination

   Address the station for the neurological and perianal findings.

   • Lower-limb neurological exam - tone, power, reflexes, sensation, straight-leg raise.
   • Perianal sensation and anal tone - a digital rectal examination is expected; loss of tone is a key sign.
   • Post-void bladder scan for residual volume / palpable bladder.
   • Vital signs and temperature.

7. 7. Arrange an emergency MRI

   Imaging is the safety-critical investigation. Name it out loud.

   • Emergency MRI of the whole spine - the definitive investigation, and it must be urgent (same day).
   • Do not wait for routine outpatient imaging.

8. 8. Refer immediately to spinal surgery

   Cauda equina is decompressed surgically, and outcome depends on speed.

   • Make an immediate, same-day referral to the on-call spinal or neurosurgical team.
   • Keep the patient nil by mouth in case surgery is needed.
   • Do not discharge - admit and escalate.

9. 9. Communicate clearly and honestly

   Explain why this is urgent without causing panic.

   • Explain in plain English that the nerves at the bottom of the spine may be under pressure and need an urgent scan.
   • Explain that early treatment protects bladder, bowel and leg function.
   • Check understanding; answer questions honestly.

10. 10. Safety-net and close

    Be explicit even though the patient is being admitted.

    • Tell the patient to report immediately any worsening numbness, leg weakness or loss of bladder or bowel control.
    • Confirm the plan: urgent MRI and the spinal team review.
    • Invite questions, thank them, close.

Common pitfalls

• Not asking about saddle anaesthesia and bladder or bowel symptoms explicitly - the single most common omission and the heart of the station.
• Performing or offering no perianal sensation check or rectal examination.
• Forgetting the post-void bladder scan for retention.
• Requesting routine rather than emergency MRI, or not naming MRI at all.
• Delaying the spinal referral, or worse, discharging with analgesia and physiotherapy.
• Reassuring the patient it is 'just mechanical back pain' before the red flags are excluded.
• Missing the malignancy and infection red flags that also need urgent imaging.

Frequently asked questions