Back Pain OSCE - Cauda Equina Syndrome

Case Overview

• Age/Sex: 67-year-old male
• Occupation: Retired mechanic
• Setting: Presents to emergency department after worsening back pain and inability to pass urine
• Chief complaint: "My back pain is terrible and I can't pee"

Patient Script

Who I Am

I'm a 67-year-old retired mechanic who lives on my own.

What Brings Me In

I came in because my back pain got suddenly much worse and I can't pass urine at all this morning.

My Story

It started about 48 hours ago with a bad ache in my lower back that’s like the usual arthritis pain I get, but it got a lot worse yesterday afternoon and then overnight I developed pain radiating down both legs and now I can hardly stand. I woke up this morning and I couldn't pass any urine — I kept trying but nothing came out, and now my belly feels very full. I also notice numbness around the area between my legs when I wiped myself. I had an episode of sciatica several years ago that settled with physio, and I have long-standing knee and lower back osteoarthritis. I did lift a heavy toolbox at home two days ago which seemed to make the back worse. I take some over-the-counter ibuprofen which helps a bit. I was worried it might be my prostate acting up — I have trouble peeing sometimes at night because of that — but this feels different and much worse.

My Medical Background

• Past medical history: hypertension, benign prostatic enlargement (diagnosed 5 years ago), osteoarthritis of lumbar spine and knees
• Medications: tamsulosin 0.4 mg nightly, amlodipine 5 mg daily, ibuprofen PRN
• Allergies: none known
• Social: lives alone, ex-smoker (20 pack-year history, quit 10 years ago), drinks alcohol occasionally
• Family: father died of prostate cancer (diagnosed in his 70s)

What I Think & Worry About

• I think maybe I’ve slipped a disc after lifting that toolbox and I’m worried I might be going to end up unable to walk.
• I’m also worried about not being able to pee — I’m embarrassed and I don’t want to be incontinent.
• I worry I might need an operation and may not get back to normal.

If You Ask Me About Other Symptoms...

• Pain: "My lower back pain is severe, worse with moving, and shoots down both backs of my thighs into my calves."
• Leg weakness/walking: "I’m unsteady and my legs feel weak — I had to sit down a few times when walking this morning."
• Sensation: "I feel numb when I wipe around my groin and buttocks — it’s weird, like pins and numbness." (patient may volunteer reduced perineal sensation when specifically asked)
• Urinary: "I tried to go since this morning and nothing came out; I had been getting up at night sometimes before, but never like this." (reports inability to void)
• Bowel: "I’ve been constipated for a couple of days, but I haven’t had any sudden loss of bowel control." (possible red herring)
• Fever/infection: "I don’t have a fever or chills."
• Sexual function: "I have noticed over months that my erections aren’t as strong as they used to be, but that’s been gradual." (chronic issue; potential red herring)
• Recent infection/UTI symptoms: "No burning or peeing frequently until today — it’s just I can’t pass anything."

---

Clinical Summary

Examination

• General: alert, uncomfortable, appears in severe pain; afebrile
• Vitals: BP 150/86 mmHg, HR 92 bpm, RR 18/min, Temp 36.8°C, SpO2 98% on room air
• Abdomen: suprapubic distension and palpable bladder fullness
• Lower limb motor power (MRC): hip flexion 4/5 bilaterally, knee extension 4/5 bilaterally, ankle dorsiflexion 3/5 bilaterally, plantarflexion 4/5 bilaterally
• Reflexes: knee reflexes 1+ bilaterally, ankle reflexes decreased 0–1+ bilaterally
• Sensory: reduced sensation to light touch in saddle distribution (perineum, inner thighs) and diminished pinprick in posterior thighs and calves bilaterally
• Rectal exam: decreased anal tone and reduced perianal sensation; anal wink absent
• Gait: unable to walk heel-to-toe due to pain and weakness
• Straight leg raise: positive at ~40° bilaterally

Investigations

• Bladder scan: 900 mL (marked urinary retention)
• Urine dip: trace blood, negative nitrites, no leucocyte esterase (no clear UTI)
• Bloods: CBC WBC 9.2 x10^9/L (normal), CRP 6 mg/L (mild), creatinine 95 µmol/L (baseline)
• MRI lumbosacral spine (urgent): large central L4/5 disc extrusion with significant compression of the thecal sac and crowding/compression of the cauda equina nerve roots; moderate canal stenosis at L3/4
• Plain radiographs: chronic degenerative changes L3–L5 (consistent with osteoarthritis)

Diagnosis

• Primary diagnosis: Cauda equina syndrome due to large central L4/5 disc extrusion.

  • Supporting evidence: acute severe low back pain with bilateral radicular leg pain, saddle anesthesia, acute urinary retention with bladder volume ~900 mL, decreased anal tone on rectal exam, bilateral lower limb weakness and reduced reflexes, and MRI showing central disc herniation compressing cauda equina.

• Important differentials:

  • Acute urinary retention due to benign prostatic hyperplasia (BPH): plausible given history of BPH and tamsulosin, but the presence of saddle anesthesia, bilateral neurological deficits, decreased anal tone, and MRI findings favor cauda equina syndrome.
  • Conus medullaris lesion: may cause early sphincter disturbance but typically presents with symmetric hyperreflexia or mixed signs and a higher lesion on MRI; imaging localizes lesion to nerve roots below conus.
  • Spinal epidural abscess or metastatic cord compression: less likely—no fever, inflammatory markers not markedly elevated; MRI excludes epidural collection but would be considered if infection risk factors present.

Management

• Immediate steps (emergency):
  • Perform urethral catheterization to decompress bladder (or suprapubic if urethral not possible) — document post-void residual and urine output.
  • Urgent MRI of lumbosacral spine if not already performed.
  • Emergency neurosurgery/spinal surgery referral for urgent decompression (surgical laminectomy/discectomy); aim for decompression ideally within 24 hours of onset of severe neurological deficits when possible.
  • Analgesia: IV opioid titration and neuropathic analgesic consideration once diagnosis addressed.
  • Consider giving IV dexamethasone while arranging surgery as temporary measure per local protocol (practice varies).
  • Baseline bloods and perioperative assessment (type and screen, coagulation profile, review antiplatelets/anticoagulants).
  • Foley catheter care and urinary monitoring, arrange inpatient physiotherapy and occupational therapy, involve urology/genitourinary nursing for ongoing bladder management and follow-up.
  • Counsel patient about possible outcomes: variable recovery of bladder, bowel, and sexual function; urgent decompression improves chances but deficits may persist.

Key Learning Points

• Cauda equina syndrome is a neurosurgical emergency: look for the red flags of severe low back pain with bilateral radicular pain, new saddle anesthesia, reduced anal tone, and acute urinary retention.
• Always perform a focused neurological and rectal examination and bladder scan in suspected cases; document findings clearly and arrange urgent MRI and surgical referral.
• Common conditions (BPH, chronic osteoarthritis, constipation) can be red herrings — correlate urinary symptoms with neurological signs and imaging to differentiate causes.