Cauda Equina and Conus Medullaris Syndromes

Etiology

Cauda equina syndrome and conus medullaris syndrome result from compression of the spinal cord and nerves/nerve roots arising from L1-L5 levels. The most common cause of compression in 45% of CES is a herniated lumbar intervertebral disc.[3]  Other causes include epidural abscess, spinal epidural hematoma, diskitis, tumor (either metastatic or a primary CNS cancer), trauma (particularly when there is retropulsion of bone fracture fragments), spinal stenosis and aortic obstruction.[4] Rare reported cases exist in which CES was associated with chiropractic manipulation, placement of interspinous devices, and thrombosis of the inferior vena cava.[4]

Epidemiology

Cauda equina syndrome and conus medullaris syndrome are rare, with an estimated prevalence of 1 in 30,000 to 100,000 people per year.[5] Estimates of annual incidence are between 1.5 to 3.4 per million people.[5] It occurs in 3% of all disc herniations.[5] Cauda equina syndrome and conus medullaris syndrome are most common in young men, possibly due to this population group being more likely to experience compressive thoracolumbar trauma.[5] One study estimated that in the U.S. we would expect to see 1016 new causes of cauda equina syndrome and 449 new cases of conus medullaris per year.[5]

History and Physical

A thorough history is necessary, with detailed questions regarding recent falls, trauma or injuries, use of anticoagulation, presented spinal instrumentation, intravenous drug use, history of malignancy, chiropractic manipulation, and constitutional symptoms like fevers/chills.[3]

Patients can present with:

• Back pain and sciatica (seen in as many as 97% of patients)
• Weakness and changes in sensation in the lower extremities
• Bladder dysfunction (disruption of autonomic fibers results in either retention or incontinence in up to 92% of patients)
• Bowel dysfunction (retention or incontinence in up to 72% of patients)
• Saddle anesthesia or decreased sensation in the perineum (in up to 93% of patients)
• Sexual dysfunction (impotence in men)[3]

The symptoms above when presenting in isolation, are neither specific nor sensitive for CMS/CES. However, several of the signs and symptoms mentioned above taken as a constellation should raise clinical suspicion.[2] These symptoms also lack significant positive predictive value for the syndromes, especially early on.[6] However, the onset of perineal anesthesia associated with bladder dysfunction is typical of the start of CES and the time at which the clock starts on diagnosis and management.[2] It is important also to note that painless urinary retention often has the greatest predictive value as a stand-alone symptom, but it is unfortunately indicative of late, often irreversible CMS/CES.[7]

Once clinical suspicion is established based on history, a thorough neurological examination is paramount. Findings to watch for include:

• Motor or sensory deficits in the legs – usually bilateral but can also be unilateral and asymmetrical (particularly in cases with an incomplete injury)
• Lower motor neuron signs in the legs – areflexia, hypotonia, atrophy (in cases of chronic cord compression resulting in CES)
• Saddle anesthesia
• Absent or decreased rectal tone
• Absent or decreased bulbocavernosus reflex
• Palpable bladder indicating urinary retention[3]

It is important to note that in the case of isolated conus medullaris syndrome, deficits of the lower extremities are more often bilateral and symmetric. Also, upper motor neuron signs can be present, such as spasticity and hyperreflexia.[1]

Evaluation

The gold standard method of evaluation for CMS/CES is obtaining urgent MRI imaging with sagittal and axial T1 and T2 sequences.[2] There has not been a specific timeframe established for “door to MRI time” in the ED, but early MRI and neurosurgical or orthopedic consultation is imperative.  An ideal goal for MRI is one hour from the patient presentation.[2] For patients with contraindications to MRI, such as those with metal implants, a CT myelogram is a viable option.[2] This imaging modality has limited utility as it requires injecting contrast through a spinal tap to visualize the spinal cord and its associated structures. A bladder scan checking for a post-void residual volume should also be obtained to evaluate for urinary retention.[2]

Treatment / Management

Prompt neurosurgical or orthopedic consultation is necessary in cases of cauda equina and conus medullaris syndromes, as the treatment is surgical decompression via laminectomy with or without subsequent discectomy, or via sequestrectomy.[2]

Differential Diagnosis

The differential diagnosis centers on non-compressible causes of spinal cord dysfunction such as:

• Spinal cord infarct
• HIV-related myelopathy
• Transverse myelitis
• Multiple sclerosis
• Syringomyelia
• Spinal arteriovenous malformation

Prognosis

Several studies have looked at prognosis and outcomes based on the timing of surgical decompression. Early intervention by surgical decompression in patients with conus medullaris and cauda equina syndromes is associated with a better prognosis, particularly when surgery occurs within 48 hours of initial presentation.[6] The longer the compression continues, the worse the permanent structural and functional impairment, and the poorer the prognosis.[2] It is important to note that the presence of bladder dysfunction prior to surgery has been linked to poorer outcomes regardless of the timing of decompression, although early decompression is still the recommendation for a better prognosis irrespective of clinical status at initial presentation.[2]

Complications

Complications in cauda equina syndrome and conus medullaris syndrome occur in a large percentage of those diagnosed. One study looked at 63-day outcomes on micturition, defecation, saddle anesthesia, sexual function, and sciatica in cauda equina syndrome. The data indicate that a large percentage of patients still experience residual symptoms irrespective of their time to surgical decompression.[3] Micturition deficits such as retention requiring self-catheterization or presence of suprapubic or indwelling catheters and incontinence still presented in 47.7% of patients.[3] Dysfunction with defecation decreased post-operatively significantly, but 41.8% of patients still had problems at 63 days post-operatively.[3] Sexual dysfunction persisted in 53.3% of patients, and saddle anesthesia in 56.6%.[3] Sciatica was present in 47.5% of patients.[3] The best predictors of outcome are neurological status at presentation and degree of injury. Incomplete injuries tend to have better outcomes.[3]