Cauda equina syndrome (CES), which occurs due to compression of the distal lumbar and sacral nerve roots, is a potentially devastating cause of back pain. CES is often missed on the patient’s initial visit which can lead to significant neurologic compromise in a matter of hours . To improve patient outcomes and minimize medicolegal risk, providers need to understand the limitations of the history and physical and carefully consider the diagnosis of CES in any patient with back pain.
Risk to the Provider
When missed, CES can lead to devastating clinical outcomes for the patient, and can also have dire medicolegal consequences for the provider. In a review of litigated cases of missed CES, Daniels et al. noted a mean award of $1.57 million for the plaintiff. Overall physicians won 60% of the cases of missed CE.
However, there were several clinical features that increased the odds of a verdict for the plaintiff. About 84% of the plaintiff verdicts involved a situation where the patient experienced permanent bowel or bladder dysfunction. Plaintiffs were more likely to win in cases when deficits developed after presentation, specifically when CES was initially missed. When patients present with incontinence, the plaintiff only won 16% of the cases .
Risk to the patient
Terminal nerve root compression in CES can weaken sphincter tone and affect detrusor strength causing urinary retention and incontinence. Typically 50% of patients will present with urinary retention (CES-R) while the remaining 50% of patients will have an incomplete syndrome (CES-I). CES-I represents the highest risk group of patients as overall outcomes are significantly improved if the diagnosis is made before it progresses to CES-R. Once urinary retention occurs, the rate of permanent neurologic disability increases significantly . If providers focus too heavily on the classic findings of urinary incontinence to make the diagnosis of CES, they may miss otherwise salvageable CES-I .
The literature regarding history and physical exam findings in cases of potential CES is limited and there is almost no literature that specifically looks at undifferentiated patients with back pain who present to the emergency department. In general, various history and exam findings may increase the likelihood of CES; however, providers should NOT overly rely on negative findings to rule out CES.
Identify a high risk history
The majority of patients with CES have a history of prior back pain. Although it can be difficult to separate acute symptoms from chronic complaints, certain elements of the history should serve as red flags for possible CES.
- Bilateral sciatica: While patients with back pain often complain of sciatica, this is typically a unilateral symptom. Any complaint of bilateral symptoms should raise the concern for CES.
- New urinary symptoms: Classically CES causes overflow incontinence, a painless loss of bladder control where patients will often not feel any need to urinate. In reality, CES-I can cause a wide variety of urinary symptoms. In a review of patients with possible CES, Bell et al. found that almost all patients with CES had some degree of urinary dysfunction including incontinence (26%), retention (30%) and frequent urination (30%). These patients had on average 2 years of back pain, with new urinary symptoms for about 4 days. The authors concluded that ANY new urinary symptoms in the setting of back pain should prompt a workup for CES .
Don’t trust a negative exam
Rectal tone, perineal sensation, and post-void residuals can be helpful when they are abnormal, but normal findings cannot rule out CES. In a series of patients with suspected CES, Balasubramanian et al. found that only 9% of patients had reduced anal tone on exam, despite of a 21% rate of CES in the same group of patients. The only exam finding that was noted to be somewhat reliable was the presence of perineal or “saddle anesthesia”, which occurred in 26% of patients with CES .
Patients with demonstrated urinary retention are more likely to have CES. Domen et al. found that 75% of patients with CES had urinary retention of more than 500 mL after voiding. When patients had urinary retention with at least two of the following clinical characteristics: bilateral sciatica, subjective urinary retention, or rectal incontinence, the MRI was more likely to show CES with an odds ratio of 48 .
Of note, ultrasound can be used to measure a post void residual (PVR) to evaluate for urinary retention . Unfortunately to date no studies have conclusively evaluated the accuracy of a negative bladder scan in terms of ruling out urinary retention and possible CES in a patient with back pain. Signs of urinary retention on bedside ultrasound may predict the presence of CES, but there is insufficient data to support using this test to rule out CES.
Consider CES with all back pain
True CES is rare. It is, however, often missed during its initial presentation which can place both the patient and provider at significant risk. Various exam findings can be used to increase the pre-test probability of CES, but no signs of symptoms are reliable enough to completely rule out CES .
That being said and from a risk management standpoint, it isn’t necessary to order an MRI on all patients with back pain, as the large majority of patients in the ED with back pain do not need further workup. In cases with a low pre-test probability, discussing and clearly documenting a normal neurologic exam and low risk of CES likely offers a reasonable degree of medicolegal protection.
Use your tests wisely
Unfortunately the literature is unclear in terms of identifying patients with back pain and pelvic region complaints who do not need imaging. To confound the picture even more, population studies have found that 5-10% of patients report baseline urinary incontinence, with higher rates reported by patients with chronic back pain . While imaging all patients with back pain and pelvic symptoms is unrealistic and will lead to an increase in the number of negative MRI’s, this needs to be balanced with the risk to the patient and provider because missed cases of CES is significant. For patients who have a realistic risk of CES, providers should have a low threshold to obtain further imaging.
This post belongs to Dr. Matthew DeLaney’s series on Everyday Risk in Emergency Medicine (EREM).
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