Cauda Equina Syndrome: A case study and review of the literature

Abstract

Spinal pathology commonly features in physiotherapy caseloads and a detailed knowledge of the features of Cauda Equina Syndrome (CES) is essential. While CES is a rare presentation, if missed the consequences of permanent bladder, bowel and sexual dysfunction are devastating. CES has a varied presentation in terms of chronology and symptomatology, leading to difficulty in accurate diagnosis in a clinical setting. The case study of a 48 year old female who developed CES while attending physiotherapy is presented. Her subjective and physical examination findings together with her lumbar Magnetic Resonance Imaging (MRI) findings are outlined. The patient underwent an L₅/S₁ subtotal laminectomy and discectomy and the patient’s status at eight months post-operatively is presented. A comprehensive review of the aetiology, sub-classifications and clinical features of CES is also provided.

Keywords

Cauda Equina Syndrome case study

1 Introduction

1.1 Case study

Mrs. D., a 48-year old female, presented to physiotherapy complaining of axial lower lumbar spine pain radiating to her left posterior thigh and posterior calf in an S₁ distribution with paraesthesia and anaesthesia in her left posterior calf (Fig. 1). Her ratio of lumbar spine to leg pain was 50:50. Symptoms were aggravated by standing greater than five minutes, walking greater than ten minutes, sitting greater than 20 minutes and bending and eased by lying down. She denied any changes in her bladder and bowel function or any impairment in her saddle sensation. Her Oswestry disability index was 50% indicating severe disability.

She reported a sudden onset of back and leg pain following prolonged flexion looking for an object in a rubbish bin five months previously. The following day, she attended her GP and was prescribed pregablin 100 mg BD and diclofenac 75 mg BD and was referred for a lumbar spine MRI scan and for assessment at a spinal triage clinic. Her lumbar spine MRI was completed two months following onset of symptoms and demonstrated a broad based posterior disc herniation at L₅/S₁ with moderate foraminal compromise and contact with the S₁ nerve roots bilaterally. Mrs. D. was assessed at a physiotherapy led spinal triage clinic and was referred to physiotherapy with a diagnosis of S₁ radiculopathy.

On examination at her first physiotherapy session she had a lateral truncal shift and her lumbar range of motion into extension was significantly restricted to of normal range. Examination of her lower limb myotomes, dermatomes and deep tendon reflexes was normal bilaterally. Straight leg raising on the right was 70 degrees and pain free and on the left was also 70 degrees but reproduced her back and leg pain.

Mrs. D attended six sessions of physiotherapy over two months. Her treatment consisted of lumbar flexibility and strengthening exercises. This resulted in a decrease in her lumbar and leg pain. At her sixth visit she reported a 24 hour history of increasing anaesthesia over her left buttock area with progression into her perineum. She also reported an increase in the severity of her lumbar and leg pain. She denied any alteration in her urinary control, urinary sensation, and bowel control or bowel sensation. On examination she had anaesthesia over the left side of her perineum and perianal region with intact sensation on the right. Previously normal neurological examination now revealed sensory impairment to light touch at L₄, L₅, S₁, S_2, S₃ and S₄ on the left but no lower limb myotomal weakness. She was referred to the Emergency Department in the hospital where a rectal examination revealed decreased rectal tone and rectal sensation. She subsequently underwent an emergency lumbar MRI two hours later. In comparison to three months previously, there was increased disc herniation at L₅/S₁ with extension of the disc material into the spinal canal, causing moderate central stenosis and compression of the descending nerve roots (Fig. 2a). Axial T2 weighted image at L₅-S₁ disc level demonstrates the large central disc herniation compressing the cauda equina nerve roots and indenting the thecal sac (Fig. 2b). The extent of the herniation is best appreciated in Fig. 2c where axial T2 weighted image just inferior to disc L₅-S₁ disc level demonstrates the large central disc herniation compressing the cauda equina nerve roots with near complete obliteration of the thecal sac. A sliver of the remaining visible thecal sac is seen posterior to the herniated disc.

Mrs. D underwent an L₅/S₁ subtotal laminectomy and discectomy the following day. Day one postoperatively, she reported that her leg pain had resolved and she had minimal back pain. She reported improvement in her saddle sensation, but it remained reduced on her left compared to her right. Following removal of her urinary catheter she had difficulty initiating the flow of urine and required re-catheterisation. She also reported impaired faecal control. Within 48 hours of surgery, both urinary and faecal impairments had resolved.

At her follow-up appointment eight months post-operatively, Mrs. D reported some residual intermittent left sided back pain on prolonged standing, rated on the numeric pain scale as 2/10. Examination revealed intact sensation at L₄, L₅ and S₁ on the left and reduced sensation at S_2, S₃ and S₄ on the left compared to the same dermatomal levels on the right. She denied any residual impairment of her bladder, bowel or sexual function.

1.2 Cauda Equina Syndrome

Cauda Equina Syndrome (CES) is a rare syndrome with an incidence of 1 in 33,000 to 100,000 [1] and accounts for 2% of lumbar discectomies [2]. CES has been described as a spectrum of low back pain, uni- or bilateral sciatica, saddle anaesthesia and motor weakness in the lower extremities with variable rectal and urinary symptoms [1].

1.2.1 Aetiology

The cauda equina (Latin for “horse’s tail”) is a bundle of spinal nerves and spinal nerve roots, consisting of the second through fifth lumbar nerve pairs, the first through fifth sacral nerve pairs, and the coccygeal nerve, all of which originate in the conus medullaris of the spinal cord [3]. These nerves have characteristics rendering them both vulnerable to injury and possessing impaired recovery following significant injury [4]. As they consist of small myelinated and unmyelinated nerves, they do not withstand compression like larger nerves. Furthermore, as compression takes place proximal or above the cell body, axons will not regenerate once wallerian degeneration occurs. Thus, injury to the cauda equina can result in irreversible damage. Failure to diagnose CES can result in devastating morbidity such as loss of bladder, bowel and sexual function. Accuracy of diagnosis cannot be underestimated.

CES occurs most frequently following a central lumbar disc herniation, prolapse or sequestration [5]. As the disc prolapses centrally, it impinges on the cauda equina. Patients who have a pre-existing narrow spinal canal may be more prone to developing CES. A narrow spinal canal may be congenital or acquired, secondary to a combination of degenerative changes in the disc and the segmental posterior joints with a resultant thickening of the ligamentum flavum. Less common causes of CES include spinal stenosis [6], epidural haematoma [7], infection [8], primary and metastatic neoplasms [9], trauma [10] and Ankylosing Spondylitis [11].

Fraser et al. [12] proposed that a provisional diagnosis of CES can be made in the presence of one or more of the following: Bladder and/or bowel disturbance, decreased sensation in the saddle area, sexual dysfunction. However clinical diagnosis of CES is fraught with difficulty and has a false positive rate of 43% even in resident neurosurgeons [13]. Woods et al. [14] outline other potential causes of bladder, bowel and sexual dysfunction and saddle anaesthesia apart fromCES.

1.2.2 Sub-classifications of CES

Three classic patterns of presentation of CES have been described [15], based on acute/chronic onset of symptoms and the presence/absence of a previous history of back pain:

Acute rapid onset of sphincter disturbance or perianal sensory loss without a previous history of back pain,

Acute bladder dysfunction with a history of back pain and sciatica,

Chronic back pain and sciatica with insidious onset of CES often with spinal stenosis.

Gleave and MacFarlane [4] described two categories of CES, CES-I (incomplete) and CES-R (retention) (Table 1). This grouping is based on the distinction whether at any given time; CES is complete or incomplete in relation to urinary function and saddle sensation. Initially the patient complains of impaired bladder/saddle sensation and difficulty with micturition (loss of desire to void/poor stream or the need to strain) but the patient remains continent (CES-I- incomplete impairment of bladder control). Saddle and genital sensory deficit is often unilateral or patchy. The presentation progresses to CES-R retention when the bladder is no longer under voluntary control with painless urinary retention and overflow incontinence. There is usually extensive or complete saddle or genital sensory deficit. A recent literature review indicates that around 50–70% of patients have urinary retention (CES-R) on presentation with 30–50% having an incomplete syndrome (CES-I) [5].

It is well established that the outcome for patients with CES-I at the time of surgery is generally favour-able, where as those who have deteriorated to CES-R have a poorer prognosis [4]. Patients with CES-I, especially if the history is less than a few days, usually requires emergency MRI to confirm the diagnosis followed by prompt decompression [5]. The urgency of surgery in CES-R is still not clear however early decompression removes the mechanical factors which can cause progressive neurological damage [5].

A recent review on CES focused on the main patterns of development and progression of this condition [16] resulted in the addition of another sub classification CES-E, (E for early). The authors assessed individual patient data from CES cases and investigated the CES progression pattern to help provide clinicians with the required information to ensure timely diagnoses. They reported the most common initial CES symptoms were perineal parasthesia and bilateral lower extremity pain, parasthesia and motor weakness. They describe CES-E as bilateral peripheral nerve dysfunction characterised by progressive sensory-motor defects from unilateral to bilateral in the lower extremities. Instead of waiting for the onset of sphincter function abnormalities, they suggest that CES should be considered as soon as CESE symptoms manifest, specifically when symptoms progress from unilateral to bilateral.

1.3 Clinical presentation

The nerves that comprise the cauda equina innervate the pelvic organs and lower limbs to include motor innervation of the hips, knees, ankles, feet, internal anal sphincter and external anal sphincter. In addition, the cauda equina extends to sensory innervation of the perineum and, partially, parasympathetic innervation of the bladder [17].

1.3.1 Pain

Patients with CES present with lumbar spine pain and bilateral sciatica which may be severe [5]. Sun et al. [16] found that bilateral sciatica was the most common symptom in CES-E cases followed by bilateral parasthesia. Indeed CES-E is characterised by progressive sensory-motor impairment from unilateral to bilateral in the lower extremities. It is important to emphasise that sciatica may be absent especially at L5/S1 with an inferior sequestration which does not compress the nerve roots [5]. However in the clinical setting the presence of bilateral sciatica should alert clinicians to suspect the possibility of CES.

Greenhalgh et al. [18] explored patient’s symptoms in semi-structures interviews with patients with confirmed CES. Patients reported the pain as severe and the most distressing symptoms in the early stages. This severity of pain may distract patients from symptoms of bladder and bowel dysfunction and the authors reported that for some patients, made questions in this regard seem irrelevant. In this context it is importance to explain the relevance of some questions to a patient who is in severe pain and provision of patient literature regarding CES may help to highlight the significance of bladder and bowel disturbance.

1.3.2 Bladder disturbance

Urinary impairments associated with CES include altered urinary sensation, loss of desire to void, poor urinary stream and the need to strain to micturate [5]. Differential diagnosis between CES-I and bladder dysfunction secondary to pain is important in a clinical setting. A patient in pain from a disc prolapse may have difficulty passing urine from mechanical factors.MacFarlane [19] outlines that a patient who has impaired voiding secondary to pain has an awareness that the bladder is full, has an intact desire to micturate, has normal sensation in the saddle area and has a tender bladder on palpation. The patient who develops CES will have one or more of the following: Altered saddle and/or urinary sensation, perineal/rectal pain, decreased awareness of bladder filling and the need to strain to maintain bladder flow. In addition, on palpation the bladder may be distended but non-tender. The onset of bladder and bowel dysfunction may begradual secondary to progressive spinal stenosis. This may not seem alarming to patients due to the gradual onset. As such continuous monitoring of bladder and bowel function during treatment is essential.

The use of urodynamic testing has been found to be useful in investigation of bladder dysfunction in early diagnosis of CES [20]. Storm [20] reported that many patients denied incontinence but had large volumes on post void residual testing. In patients with suspected CES who deny bladder dysfunction assessment of post void volumes using urodynamic testing may provide valuable information. In a prospective study of CES, the severity of bladder dysfunction at the time of surgery was significantly associated with recovery of bladder function [21].

While bladder dysfunction has been reported in 88.9% of CES cases [22], it is important to remember that bladder involvement is not always present in CES as this case study demonstrates. In CES-E, Sun et al. [16] found that sphincter dysfunction was only the initial symptom of CES in patients with acute onset of CES or ankylosing spondylitis. Rooney et al. [23] performed a retrospective study of 66 patients with symptoms suggestive of CES who were investigated with MRI. The authors compared the clinical findings of those who’s MRI scan did not show a radiological abnormality with those who’s MRI demonstrated an abnormality. They concluded that there were no significant differences between those with abnormal imaging and those with a normal scan. Specifically with regard to urinary symptoms, urinary incontinence was present in 42% and urinary retention in 34% of patients with confirmed CES on MRI. Thus 58% of patients with confirmed CES did not present with urinary incontinence. Decreased urinary sensation was present in 36% of patients with confirmed CES. However those with normal imaging also had a high frequency of urinary impairment with incontinence present in 54% of patients, urinary retention in 53% of patients and decreased urinary sensation in 50% of patients. In a clinical setting the presence of urinary symptoms alone is not predictive of a diagnosis of CES. Equally, patients who have CES may not present with urinary symptoms.

1.3.3 Bowel dysfunction

Bowel dysfunction associated with CES includes an inability to control defecation [24] and inability to sense rectal fullness [25]. Gleave and MacFarlane [4] report that bowel dysfunction is seldom noticed acutely in complete CES because of an inability to appreciate filling of the rectum. In addition, as urinary excretion occurs more frequently than bowel excretion [4], urinary dysfunction will be more apparent to patients than bowel dysfunction. Korse et al. [22] reported that 47.1% of patients with CES had bowel dysfunction at initial presentation.

In the early stages, the patient may complain of constipation secondary to the loss of parasympathetic innervation to the descending colon, while simultaneously anal tone may be lax. Faecal incontinence generally occurs late in CES and its absence should not be considered reassuring [4]. CES has been diagnosed on the basis of other symptoms including perianal sensory loss [26], sexual dysfunction [27] and bilateral lower limb symptoms [28].

1.3.4 Saddle sensation

Saddle anesthesia is defined as anesthesia or paraesthesia involving S₃ to S₅ dermatomes including the perineum, external genitalia and anus; or more descriptively, numbness or “pins-and-needles” sensations of the groin and inner thighs which would contact a saddle when riding a horse [29]. In CES-I saddle sensory deficit is often unilateral or partial [5]. In CES-R there is usually extensive or complete saddle sensory deficit. Gardner et al. [5] recommend that assessment of saddle sensation should involve light touch and pin-prick sensation

Sun et al. [16] found that one of the most common initial CES symptoms was perineal parasthesia. However Rooney et al. [23] found that saddle numbness was present in 71% of patients with no relevant abnormality on MRI. In spite of this, emergency MRI is indicated in this group of patients. It is recognised that 40% of out of hours MRI scans for the investigation of CES will be ‘normal’ but this is considered a reasonable outcome [30].

1.3.5 Other features

Several other clinical presentations of CES must be considered. The importance of testing anal tone is well documented in the diagnosis of CES. Physical examination should include assessment for voluntary control and reflex contracture [31].

In the Sun et al. [16] analysis of the initial presenting symptoms in CES, reduction of sexual function and sexual dysfunction were not common initial presenting complaints. This finding was confirmed in a study by McCarthy et al. [1] who reviewed 42 patients two years following surgical decompression for CES. They reported that only one patient noticed erectile dysfunction at initial presentation. However at follow-up, 47% of the males reported erectile dysfunction.

Other issues including medication can cause symptoms that can mimic CES. Analgesia’s frequently prescribed for lumbar spine pain such as opioid analgesics (Codeine or Tramadol) are frequently associated with constipation. Recent work has highlighted the side effects of anticonvulsant drugs commonly prescribed for radicular pain such as gabapentin or pregablin which include altered sensation, urinary incontinence or retention and sexual dysfunction [32]. Clinicians should take due consideration of prescribed medications as a possible cause of CES signs and symptoms.

Patients may not mention symptoms of urinary, bowel or sexual dysfunction due to embarrassment. Narrative analysis from the Greenhalgh and Selfe study [18], identified two factors that should influence clinical practice with regard to CES; a) clinician’s awareness of the clinical features and an ability to create a similar awareness in patients and b) communication of these clinical features in a clear language that patients and clinicians understand. Physiotherapists should be directed to an excellent resource from Gloucestershire Hospitals Trust on early recognition of CES [33]. This document ‘sets out evidence information recommendations to facilitate best practice in clinical decision making and timely action by Physiotherapists when assessing patients with potential or actual Cauda Equina Syndrome’. The guideline has an accompanying questioning proforma to direct questioning regarding bladder, bowel, sexual and sensory impairment.

1.4 Clinical implications

Spinal pathology is a routine part of physiotherapy caseloads and a detailed knowledge of the features of CES is essential. While CES is a rare presentation, the consequences of permanent bladder, bowel and sexual dysfunction are devastating. CES has a varied presentation in terms of chronology and symptomatology, which may not be elicited by the standard bladder and bowel questioning. It is important to explain the relevance of questioning to a patient in severe pain. Finally, it is vital to identify patients who are developing symptoms of CES-I at an early stage to maximise their chances of avoiding long term complications.

Conflict of interest

None to declare.

Footnotes

Acknowledgments

Thank you to the patient featured in the case study for giving her consent to publish.

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