Cauda Equina Syndrome
Introduction
The Cauda Equina (from the latin horse’s tail) is the bundle of spinal nerves that descend from where the spinal cord tapers to an end at the conus medullaris at approximately L1. It transmits motor and sensory impulses to the lower limbs, motor innervation to the anal sphincters, and parasympathetic innervation for the bladder.
Cauda equina syndrome is a rare constellation of symptoms and signs resulting from severe compression of the descending lumbar and sacral nerve roots at the base of the spinal cord. It is considered a diagnostic and surgical emergency because delays in detection and intervention can potentially result in irreversible weakness.
By far the most common cause is disc herniation. Other causes include trauma, malignancy, infections and progressive spinal canal stenosis.
Clinical Features
Symptoms
Symptoms may develop acutely or progressively over time
Pain
localised in the back or radiating into the legs.
Typically sciatica type pain. Bilateral sciatica = red flag
Parasthesia
To lower limbs or perineum. (saddle paraesthesia)
Lower extremity weakness
pattern of weakness depends on level affected
Bladder dysfunction
Urinary retention, incomplete voiding, overflow urinary incontinence
Patient may not be aware when passing urine due to saddle paraesthesia
Bowel dysfunction
Constipation and/or faecal incontinence
Erectile Dysfunction
Signs
Lower motor neuron signs
Variable motor and sensory loss in lower limbs
Decreased or absent reflexes
Hypotonia or atrophy of legs in chronic presentations
Urinary retention
post void residual of > 200mls on bladder scan/US
Decreased or absent anal tone on PR exam
Reduced or absent sensation in perineal area (S2-S4 innervation)
Red Flags in Acute Lower Back Pain
History
PHx Cancer
Weight loss
Immunosuppression
Prolonged steroid use
IVDU
Pain unrelieved by rest
Fever
Significant trauma
Bowel or bladder incontinence
Urinary retention
Exam
Motor weakness in lower extremities
Saddle anaesthesia
Loss of anal tone
Absent reflexes
Fever
Focal vertebral body tenderness
Differential Diagnosis
Muscular lower back pain
Sciatica
Compression fracture (May be non-traumatic in the setting of osteoporosis)
Non compressive causes of spinal cord dysfunction
MS, Transverse myelitis, Spinal AVM, Spinal cord infarction
Abdominal aortic aneurysm
Clinical Investigations
Bedside
Urinary BHCG – all women of child bearing age
POCUS – if any concern for AAA
Bladder scan or POCUS to assess post void residual if bladder symptoms
Laboratory
FBC, CRP – raised inflam markers concerning for infection/malignancy
Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 13942
Radiology
MRI Lumbar Spine = diagnostic test of choice
Should be obtained urgently including out of hours if symptoms and signs of Cauda Equina
Management and Disposition
Symptomatic Treatment
Multimodal analgesia
Urinary Catheter if patient in retention.
Specific Treatment
Once diagnosis is confirmed high-dose steroids may be prescribed to reduce any localized swelling
Definitive treatment is urgent surgical decompression.
Disposition
If concerned for Cauda Equina patient should not be discharged from emergency dept without MRI Lumbar spine
Once diagnosis is confirmed patient should be admitted under spinal surgery service for emergency decompression
References
NICE Guideline Low Back Pain and Sciatica 2016 (NG59)
Cauda Equina and Conus Medullaris Syndromes – www.emedicine.medscape.com
Levin K et al, Acute lumbosacral radiculopathy – www.uptodate.com
Tintinalli J. Tintinalli's Emergency Medicine. 9th ed. McGraw-Hill Education; 2019.
This blog was written by Dr. David Hogan and was last updated in October 2020