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

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,

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.

1.3.1 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.