NeurologyTier 1Disease (DEADMAN)

Cauda equina syndrome

Description

Compression or injury of the lumbosacral nerve roots + filum terminale within the spinal canal
Cord ends as the conus medullaris at ~L1/L2 in adults - a canal lesion below L1/L2 hits the cauda equina, not the cord
- Hence a lower motor neurone syndrome. UMN signs mean the lesion is at or above the conus
Surgical emergency - the deficit becomes permanent

Clinical grades - drive urgency and prognosis

	Bladder
CESS (suspected)	Bilateral radicular pain / red flags, no objective sphincter deficit
CESI (incomplete)	Altered urinary sensation, loss of desire to void, poor stream, straining - but still voiding voluntarily
CESR (retention)	Painless retention with overflow incontinence - much worse outcome; the point at which the window has largely closed
CESC (complete)	No bladder/bowel function, patulous anus, complete saddle anaesthesia

The whole management aim is to operate while still CESI

Cauda equina vs conus medullaris

	Cauda equina	Conus medullaris
Onset	Gradual, asymmetric	Sudden, symmetric
Pain	Severe radicular	Less prominent, back pain
Weakness	Marked, LMN, asymmetric	Mild, may be UMN
Reflexes	Absent ankle jerks, downgoing plantars	Preserved/brisk knee jerks, upgoing plantars
Sensory	Asymmetric saddle, dermatomal	Symmetric saddle, dissociated
Sphincter	Later, asymmetric	Early and prominent

Epidemiology

Rare: ~1-3 per 100,000/yr; ~2-6% of lumbar disc surgery
Peak 30-50 years for disc-related disease; older for malignancy and stenosis
M=F
One of the highest-value medicolegal diagnoses in medicine - missed diagnosis is the commonest neurosurgical claim

Aetiopathogenesis

Compressive

Large central/paracentral disc herniation - commonest (~45%), usually L4/5 or L5/S1
Malignancy
- Metastatic - prostate, breast, lung, renal, thyroid; myeloma
- Primary sacral bone - chordoma; leukaemic infiltration; CNS tumour drop metastases
- Intrinsic conus/filum tumours - ependymoma (the classic midline conus tumour), dermoid, lipoma
Epidural abscess - IVDU, bacteraemia, diabetes, recent instrumentation
Epidural haematoma - anticoagulation, post-procedure (LP, epidural)
Severe degenerative canal stenosis; spondylolisthesis; trauma/burst fracture
Iatrogenic - post-surgical, intrathecal chemotherapy

Non-compressive - the differential that gets missed

Infective - herpes simplex / varicella (Elsberg syndrome), CMV (HIV - lumbosacral polyradiculitis), TB (Pott's), Lyme, schistosomiasis
Inflammatory/granulomatous - sarcoidosis, ANCA-associated vasculitis, Behcet
Autoimmune neuropathy - GBS, CIDP (these are polyradiculopathies, not compression - the CSF and MRI tell you)
Neoplastic meningitis - carcinoma (breast, ovarian, lung), lymphoproliferative disease
Congenital - spina bifida, tethered cord
Arachnoiditis; spinal AVM/dural fistula

Mechanism

Roots lack epineurium and have a watershed blood supply -> vulnerable to mechanical compression + venous congestion + ischaemia
Ischaemia is why time matters more than the size of the disc

Diagnosis

Red flags to ask in every back pain presentation

Bilateral (or alternating) sciatica
Saddle / perianal numbness (S2-S5) - ask about wiping and toilet paper sensation explicitly
Bladder - loss of the urge to void, altered urinary sensation, poor stream, straining, painless retention, overflow incontinence
Bowel - loss of anal sensation, faecal incontinence, constipation
Sexual - erectile dysfunction, loss of genital sensation
New gait disturbance

Examination

Bilateral, possibly asymmetric LMN weakness of both flexors and extensors
Reduced or absent reflexes (esp. ankle jerks) with FLEXOR plantar responses
Saddle sensory impairment S2-5 + reduced anal tone; test the anal wink and perianal pinprick, and document it
*No UMN signs - if present the lesion is at the conus or above*
Post-void residual bladder scan - >200 mL is significant; the single most useful bedside objective test
Midline conus lesion: bilateral symmetrical signs progressing in sacral dermatome sequence, with ankle jerk loss and L5/S1 weakness appearing late
Clues to a non-disc cause: vesicular rash over the lumbar dermatomes (HSV/VZV), erythema nodosum (sarcoid, TB, Behcet), inguinal lymphadenopathy (lymphoproliferative), fever/spinal tenderness (abscess), weight loss (malignancy)

Imaging

Urgent MRI whole spine with contrast - the only adequate test
- Target: scan within 4 hours of the request; 24/7 access is now the expected standard of care
- Whole spine, not just lumbar - a thoracic cord lesion mimics this and metastases are multilevel
CT myelogram if MRI contraindicated
A normal MRI does not end the assessment - proceed to CSF for the inflammatory/infective mimics

Bloods and CSF

FBE, CRP/ESR, blood cultures if abscess suspected
PSA, myeloma screen, EPG/SFLC if malignancy suspected
CSF (only once compression excluded): cytology, protein, PCR for HSV/VZV/CMV, ACE, culture/AFB

Management

A. Compressive cauda equina - time-critical

Urgent neurosurgical/spinal referral the moment it is suspected - do not wait for imaging to refer
Surgical decompression as an emergency, ideally within 24 h of onset and as early as possible
- Outcomes are better with earlier surgery and are markedly worse once CESR (painless retention) is established
Catheterise; strict fluid balance; analgesia; VTE prophylaxis
Dexamethasone if malignant compression (see spinal cord compression); no role for steroids in disc-related CES

B. By cause

Cause	Treatment
Disc herniation	Emergency discectomy/laminectomy
Metastatic	Dexamethasone + urgent radiation oncology/spinal surgery; treat the primary
Epidural abscess	Surgical drainage + IV antibiotics (empiric cover for S. aureus incl. MRSA); blood cultures before antibiotics
Epidural haematoma	Reverse anticoagulation immediately, urgent evacuation
HSV/VZV (Elsberg)	IV aciclovir
Sarcoid / vasculitis	High-dose corticosteroid + steroid-sparing immunosuppression
GBS / CIDP	IVIg or plasma exchange (not surgery)
Neoplastic meningitis	Intrathecal chemotherapy, radiotherapy, palliative care input

C. After decompression

Bladder - trial of void, intermittent self-catheterisation, urodynamics; urology follow-up
Bowel - regimen from the outset, digital stimulation, suppositories
Sexual function - address explicitly; it is the deficit patients complain of least and suffer from most
Rehabilitation, pressure care, neuropathic pain management
Document the pre-operative neurological examination in full - this is the single most litigated record in the notes

Associations

Lumbar disc disease, spinal canal stenosis, spondylolisthesis
Metastatic malignancy - prostate, breast, lung, renal, thyroid, myeloma
Ankylosing spondylitis (late cauda equina syndrome with dural ectasia)
Anticoagulation, spinal/epidural anaesthesia, lumbar puncture
IVDU, diabetes, immunosuppression (epidural abscess)
HIV (CMV polyradiculitis), sarcoidosis, Behcet
Neural tube defects, tethered cord

Natural history & complications

Outcome is determined by the deficit at the time of surgery, not by the size of the lesion
- CESI decompressed early -> most recover bladder function
- CESR -> majority have permanent bladder, bowel and sexual dysfunction
Motor and pain recovery generally better than sphincter and sensory recovery
Recovery continues for up to 2 years

Complications

Permanent neurogenic bladder -> recurrent UTI, hydronephrosis, renal impairment
Faecal incontinence and constipation
Sexual dysfunction - erectile failure, anorgasmia, loss of genital sensation
Chronic neuropathic pain; saddle anaesthesia
Foot drop, gait impairment, falls
Pressure injury; depression; loss of employment
Missed or delayed diagnosis is the leading cause of neurosurgical litigation - re-examine and re-document if the story changes

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