How useful is the physical examination in suspected cauda equina syndrome?

Background

Cauda equina syndrome (CES) is a syndrome consisting of one or more of the following:

(1) bladder and/or bowel dysfunction,

(2) reduced sensation in the saddle area (i.e. the perineum and inner thighs), and

(3) sexual dysfunction, with possible neurological deficit in the lower limb (motor/sensory loss or reflex change) [1].

The cauda equina is a latin name meaning horse’s tail and represents nerve roots L2 through L5. CES is caused by compression of the cauda equina in the spinal canal secondary to some local mechanical process (e.g. disc herniation, tumour, infection, stenosis, hematoma or inflammation). It can also occur secondary to vascular complications (i.e. AAA) [2]. It is a relatively rare condition that has an estimated incidence between 1 in 33,000 – 100,000 [3]. There is a disproportionately high risk for medicolegal consequences with missed diagnoses as failure to diagnose this condition in a timely manner can lead to significant morbidity for the patient including loss of bowel, bladder, and sexual function [4]. Thus, it would be ideal for physicians to be able to diagnose CES early in the patient presentation based on physical examination findings.

The Case

A 30-year-old carpenter presents to your ED with a 4-week history of lower back pain with sciatica that started after he attempted to lift a large pile of drywall. He tells you, “Doc I’ve had pins and needles all the way down to my feet the past month”. Today, after trying to move his couch at home the pain suddenly worsened. Since then he has had difficulty walking, voiding, and tells you he can’t feel his butt when he sits down. You are concerned for cauda equina syndrome.

The Clinical Question

How useful is the physical examination in an adult patient with suspected cauda equina syndrome?

The Evidence

1. Kennedy (1999) [5] performed a retrospective review of 19 patients with CES presenting to the National Spinal Injuries Unit in Ireland over 7 years. Complete perineal anesthesia was evident in 7/19 (35%), bladder dysfunction in 19/19 (100%) with 12/19 (63%) regarded as significant and decreased anal tone in 15/19 (79%). Eleven patients had weakness of the extensor halluces longus (58%), 12 reduced subtalar eversion (63%), and 6 with plantar flexion weakness (32%). Finally, 12 patients (63%) had absent or reduced ankle reflexes, while 8 patients (42%) had absent or reduced knee reflexes.
2. In 2007, Dr. Jallah and Minhas [6] reviewed the charts of patients treated for CES at their hospital over a 4 year period (n = 32). Only 19% of patients presented with the classic combination of bilateral sciatica, lower limb weakness, saddle anesthesia, and sphincter disturbance. Urinary symptoms were present in 84% and rectal symptoms in 35% of patients. Of the 23 charts commenting on anal tone, 78% were abnormal. The following abnormalities were also noted: sensory loss in legs (30%, n = 30), sacral (85%, n = 27), perianal (75%, n = 24) and motor loss (32%, n = 31) with reflex loss of the knee (9%, n = 22) and ankle (46%, n = 22).
3. A retrospective study by Domen in 2009 [7] analyzed 58 consecutive cases of suspected CES presenting the hospital’s emergency room. Eight of the 58 patients had confirmed CES on MRI. Patients with measured urinary retention of more than 500 ml alone or in combination with at least two of: bilateral sciatica, subjective urinary retention, or rectal incontinence symptoms, were more likely to demonstrate CES on MRI with an odds ratio of 48.
4. A retrospective study by Rooney in 2009 [8] examined 66 patients admitted to the neurosurgical unit over a 10 month period with suspected CES. There were no significant differences between those with abnormal imaging (52%) and those with normal imaging (48%) for features recorded on physical examination.
5. A retrospective study by Gooding in 2013 [9] looked at 57 patients with suspected CES referred for an MRI. Thirteen of the 57 patients had confirmed CES on MRI. They concluded that there is no significant link between any single clinical feature or any combination of signs and symptoms with MRI outcome. They specifically commented that digital rectal examination offers no significant diagnostic value (p=0.897, test accuracy 51%, diagnostic odds ratio 1.42) in the assessment of patients with suspected CES and the results of this physical examination finding should not alter the need for or against an MRI. The suspicion for CES and need for MRI should be based on the clinician’s overall gestalt of the patient’s condition.
6. Another retrospective study in 2013 [10] reviewed a database of 40 medicolegal cases of CES. Of the 28 patients who had physical examination findings recorded, 27 patients had impairment of perianal sensation. Anal tone was normal in 1 of 3 patients with an early presentation of CES and one in 5 patients who had recently developed urinary retention. Anal tone was impaired in all patients presenting later on in the course of CES with loss of bladder sensation and function.[bg_faq_end]

Summary Chart of Test Characteristics

Download a copy of this here!

Table 1 – Sensitivity, Specificity, positive and negative likelihood ratios of physical exam findings compared to MRI findings of CES.

*Summary of physical exam findings from [7,8]. Adapted from the Web Appendix of [11].[bg_faq_end]

The Bottom Line

The few studies conducted thus far are retrospective, small in sample size, and of lower tiers of evidence. Overall, there is poor evidence that any individual physical examination finding could be used to rule in or rule out CES. However, as suggested by Domen and his colleagues, a urinary retention of more than 500 mL alone (Sn 1.00, Sp 0.94, +LR 16) or in combination with two or more specific clinical characteristics may be important predictors for CES. The volume of post-void urinary retention is quite variable depending on the study and other studies have found a post-void residual of >300 mL alone achieved a sensitivity of 90% for CES (CanadiEM Tinytip).

Clinicians need to rely on their overall gestalt of the patient presentation combining history and physical examination. With the high risk of litigation surrounding CES cases, it is still important to document a detailed physical examination. Since the potential for patient morbidity with a missed diagnosis is high, if CES is suspected, get the MRI!

This post was copyedited by Rob Carey(@_RobCarey)

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Reviewing with the Senior

When reviewing Cauda Equina Syndrome (CES) with your EM attending or Ortho/Neuro Surgical resident on call there are several key points that should be captured. From the perspective of the Spine Surgery team (which can comprise of either orthopedics or neurosurgery or both), CES is most often viewed as a surgical emergency requiring decompression within the first 48 hours of presentation of symptoms.
1. Order and timing of symptoms onset.
2. Severity of symptoms i.e. loss of sensation to soft touch and/or pin prick
3. Associated tests that have been ordered and arranged.
4. Is the patient aware of the possible severity of their condition?

The reason for this information being so pertinent is that it can help with surgical and resource planning as time is always an issue with work up, diagnosis, and intervention with this uncommon disorder. Depending on the length of symptoms, this can determine if emergent surgery is warranted as well as facilitate in the discussion for possible outcomes with the patient regarding success of surgery. Likewise, the severity of symptoms can have an impact on expected outcomes when consenting for the procedure. The MRI is the gold standard imaging and work up tool that all of the previous tests were compared to in the table above. If CES is expected, by all means call the surgical consultant service prior to having an MRI done, however, please ensure that an emergent MRI is arranged or will be arranged by the ED.

Lastly, as with all emergent and possible life changing pathology, please notify the spine consultant of the extent of which you have discussed the pathology with the patient. No one wants to drop bad news on a patient that they suspected was already informed or re-break bad news slowly in an emergency.

Colm McCarthy

Orthopedic Surgery R4 Mcmaster University

@ColmJMcCarthy

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Taft Micks

Family Medicine Resident, Memorial University

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