Acute onset low back pain leading to a diagnosis of cauda equina syndrome: a case study

The incidence of patients presenting to their primary care practice with new onset lower back pain (LBP) is around 20% of the UK population at any one time (National Collaborating Centre for Primary Care, 2009). It is cited among the most common symptoms managed in primary care (Greenwood and Shipley, 2017), with a myriad of potential diagnoses (Innes et al, 2018). With the relatively new addition in extended roles of the primary care advanced nurse practitioner (ANP), it is paramount that they are able to safely assess, examine, diagnose, and mange this generic symptom effectively.

One less common, albeit time-critical, condition to consider with LBP is cauda equina syndrome (CES) (Long et al, 2020). Much of the literature indicates the complexity yet urgency of the diagnosis, instigating the need for a robust clinical history and examination to be performed. Emphasis has been placed on ensuring risk stratification and red flag criteria be addressed (National Institute for Health and Care Excellence (NICE), 2021).

This article will discuss in detail a case study of a patient, who was reviewed in a GP practice by an ANP, displaying symptoms of new onset LBP, with associated radiation of sciatic pain down one leg (Table 1). Discussion will involve synthesis of the symptoms presented, with emphasis on the advanced clinical decision making by ANPs in primary care. An evaluation consolidating the diagnosis of CES via a review of the history and clinical examination will be sought. Analytical debate, using current knowledge and evidence-based research available around the condition will be also be demonstrated. There will also be attention around differential diagnoses that these symptoms may be caused by, leading to a conclusion of the overall clinical management plan and considerations that should be made by ANPs that work in the primary care sector.

Cauda equina syndrome

CES is documented as a rare and challenging neurological condition to diagnose (Greenhalgh et al, 2018). It is defined by Zusman et al (2020) as a significant compression of the nerve roots in the spine via full or partial occlusion of the nerve pathways, leading to a reduction in or absence of lower sacral nerve function, caused by a multitude of potential aetiology.

The cauda equina (CE) comprises a set of 20 nerve roots originating from the conus medullaris, found at the terminal end of the spinal cord (Finucane et al, 2020). Long et al (2020) illustrate that this group of nerves resemble strands of the horse's tail, giving rise to the Latin phrase ‘cauda equina’. A French anatomist, Andre Du Laurens in 1595 coined the term due to its appearance (Quaile, 2019). The CE is housed within the spinal canal at lumbar region L1-L5, through into the sacral region S1-S5, and coccygeal region 1-3. The lumbar and sacral nerve roots lead into the sacral plexus, which contains the largest and longest nerve in the body, the sciatic nerve (Kavanagh and Walker, 2013). These nerve roots are responsible for various sensations and motor activity of the lower extremities, via their action potentials, controlling both voluntary and involuntary reactions through the sympathetic and parasympathetic nervous systems (Scioscia, 2017).

The spinal column contains several structures including vertebrae, discs, nerves, muscles, ligaments and vasculature. If any of these structures are compromised, this can lead to reactive, degenerative and inflammatory responses. Vertebral discs are made up of water and collagen, acting as shock absorbers to stressors of the spine. Disc degeneration and/or bulging can occur due to time, trauma, continued stress or pathological changes (Eames, 2020). Kavanagh and Walker (2013) corroborate the above compression theory.

There are many documented causes of CES; however, Grasso et al (2020) report 45% of cases originate from disc herniation. Other causes mentioned by Greenhalgh et al (2018) include:

• Traumatic injury
• Spinal lesions
• Infections such as osteomyelitis of the spine
• Arthritis
• Vascular lesions
• Osteoporotic fractures, malignancy or metastases and
• Spinal stenosis.

CES was first publicised in 1929 by Dandy, cited by Caputo and Cusimano (2002), as a condition with a high risk of disablement, and increased levels of medico-legal, surgical, and socioeconomic implications. It therefore requires immediate referral for acute investigation, and timely surgical intervention, namely spinal decompression (Mayo and Herdman, 2020). Woodfield et al (2018) and Mizra et al (2020) both report an estimated incidence in the UK of 1.9 patients per 100 000 people, with 15-31 diagnosed patients in any single UK tertiary centre per year. Finucane et al (2020) quantify an overall prevalence ranging between 1 in 33 000, to 1 in 100 000. Greenhalgh et al (2018) cite a low prevalence of patients in primary care at 0.002% yearly. This means the likelihood of a GP/ANP seeing a true case of CES is one in their career. Eames (2020) adds that many GPs/ANPs will never see a true case.

Despite its scarcity in primary care, it has huge implications on both the patient and health services, therefore ANPs need to consider the signs and red flags when assessing such patients. The costs to the patients' long-term recovery and rehabilitation, both physically and psychologically, has been well documented. It can impact on all activities of daily living, including reduced mobility, incontinence, and lack of sexual function. Screening and timely referral is therefore deemed paramount, as mentioned in guidelines worldwide (Germon et al, 2015).

Financial burden

There is a huge financial burden attached to CES. This is mainly in regards to litigation claims (Quaile, 2019). Kavanagh and Walker (2013) reported a high incidence of upheld medical defence union claims in 2004, equating the average pay out per patient as £336 000. Mizra et al (2020) state that between 2010-15, there were 293 claims relating to CES, with a total of £25 million compensatory payouts. CES equates to around 23% of claims in England alone, blamed on missed or delayed diagnosis (Eames, 2020).

Risk factors

Demographically Long et al (2020) suggest a correlation of age below 55 years, females, and obesity with CES. Quaile (2019) agrees with obesity; however, disagrees on age and gender, proposing previous surgical intervention as a risk factor. Kaiser et al (2020) disputes age and obesity as risk factors, citing small retrospective studies coupled with the low incidence of CES, creates uncertainty in attributing true demographic risk factors. Despite this, many guidelines include the above as considerations when stratifying risk of CES (Finucane et al, 2020).

Cauda equina symptoms

The symptomology of CES is the centre of much debate in the literature. Caputo and Cusimano (2002) discuss CES symptoms as involving LBP, bilateral sciatica, lower motor and sensation dysfunction, with disruption of urinary or bowel function. Zusman et al (2020) add that symptoms vary, although should include bilateral sciatica. Khot and Polmear (2006), and Kinirons and Ellis (2005) agree with this. Long et al (2020) indicate a low threshold for investigation of any LBP to rule out CES. Germon et al (2015) introduces the presence of LBP and/or sciatica, with bladder/bowel instability, and/or saddle anesthesia need urgent referral for investigation. Two papers, Pronin et al (2020) and Kaiser et al (2020), omitted the presence of LBP or sciatica as primary factors of CES. They credit most important symptoms to be saddle anesthesia, bowel/bladder/sexual dysfunction, and loss of lower extremity sensation or function. A White Paper on CES by Wilkes (2019) found that relying on the symptoms of bladder/bowel dysfunction, or sensory/motor loss, may be a late sign of CES, therefore damage from compression had likely already occurred.

Thakur et al (2017) and Quaile (2019) summarise CES as a collection of symptoms, with no bias to the most common, incorporating any impairment of the main functions of the nerve roots in the CE. Zusman et al (2020) agree with the above, emphasising symptoms depend on the degree of nerve root occlusion. In response to conflicting CES symptoms, Finucane et al (2020) reviewed international papers to provide a robust framework for assessing and sign-posting potential patients with CES for urgent investigation, aiding clinicians from any background to effectively triage patients.

Presenting complaint of case

The presenting complaint in the case study was LBP with sciatica. LBP is attributed as one of the most common complaints in primary care, with 15-20% of patients at any time complaining of this. Approximately 60% of adults will have suffered LBP in their lifetime, ranging from traumatic or mechanical manifestations, to more complex vascular and neurological conditions (Khot and Polmear, 2006). Finucane et al (2020) report a 0.004% prevalence of LBP in primary care caused by CES. Long et al (2020) concur with this. Greenhalgh et al (2018) found 1% of all LBP was attributed to CES in a 1994 study. Although LBP was found to be present in patients diagnosed with CES by Kavanagh and Walker (2013), they highlight it was not the most sensitive symptom without the presence of other lower extremity factors, as in this case.

Sciatica

Sciatica becomes a more specific symptom, indicating potential nerve root compromise (Eames, 2020). The pain and radiation into one or both legs is thought to be caused by the occlusion of any nerve roots in the lumbosacral region (Ahad et al, 2015). Sciatica is a misunderstood term by some clinicians and patients alike. Kinirons and Ellis (2005) highlight true sciatica involves pain that radiates into the buttocks, down into the thigh, lateral or posterior aspect of calf, into the ankle then foot, leading to reduced extension of toes, and straight leg raise (SLR). This is supported by Germon et al (2015) as a sign to consider urgent referral for MRI scanning.

Much discrepancy lies within the literature regarding bilateral and unilateral sciatica. Bilateral sciatica is highlighted in NICE (2020) red flags for CES. Longmore et al (2003) conflictingly mention asymmetrical sciatica in CES. United Kingdom Spine Societies Board (UKSSB) (2020) explain that there is a poor evidence-base on bilateral sciatica, as research is largely based on small retrospective studies in secondary care. They suggest consideration of unilateral symptoms progressing to bilateral being a red flag. Domen et al (2009), cited by Kavanagh and Walker (2013), found that the presence of bilateral sciatica was not statistically significant, whereas LBP and urinary retention was present in 75% and 87.5% of the patients in the small single-centre trial. Many papers contradict the need for bilateral leg symptoms. Higginson et al (2020) support the view of huge discrepancies in CES symptomology, proposing further research involving longer and larger prospective studies.

Abnormal gait

On cursory observation of the case study patient, an abnormal gait was exhibited. Initial inspection forms the first part of any clinical examination, particularly musculoskeletal and neurological, highlighting obvious abnormalities (Model, 2006). The patient walked into the consultation on tip toes with grimaced face. Innes et al (2018) mention gait change as a red flag sign for CES. This was the only reference to gait in the literature read. It likely relates to the effects of pain sensors, release of adrenaline, and neurotransmitters within the body that control balance, and muscle tension (Swift, 2018).

History taking

Finuacane et al (2020) advocate deep exploration of the history of symptoms, providing examples of questioning that are useful to extrapolate more succinct information. This improves documentation of the presenting findings. Through further history taking, adopting the acronym SOCRATES, as per Innes et al (2018), the patient reported sudden, sharp pain without trauma, worse around the lumbar region and buttocks. It increased on movement and sitting down, and did not respond to analgesia.

Following the presenting symptoms, a history of the complaint was sought. The patient reported poor bladder and bowel control recently: urge incontinence. They did not associate this with their LBP due to recent childbirth. Pronin et al (2020) discussed this, implicating lack of relevance, and the sensitive nature of symptoms deterring patients from reporting this during history taking. Greenhalgh et al (2018) therefore encourage clinicians to use careful and appropriate language, to ensure thorough accurate symptoms are explored.

Quaile (2019) found a consensus of bladder instability for possible CES, citing nine guidelines internationally. Woodfield et al (2018) mention bowel/bladder problems to be the main concerns of CES, likely causing lasting neurological deficit, thought to have a direct relation with the degree of compression. Grasso et al (2020) categorise CES into two types; complete and incomplete compression. Incomplete was seen as more favourable to identify, displaying symptoms of bladder/bowel incontinence, potentially leading to improved recovery. Complete was found to cause urinary retention and constipation rather than incontinence. This would therefore indicate that the patient in the case study was likely incomplete CES.

During the history-taking, the patient was asked if they had experienced any lack of sensation of their buttocks, and/or genital area. Finucane et al (2020) suggest asking patients about numbness in buttocks, and/or genitals, as saddle anesthesia is a strong predictive factor in CES due to the involvement of sacral nerve compression. Kavanagh and Walker (2013) recognise that the majority of disc herniations occur at L4/L5, and L5/S1 around the sacral plexus, which is responsible for anal tone, and genital sensation. As in the case study, Greenhalgh et al (2018) report not all patients will recall slight changes in bladder or bowel, as well as numbness or lack of sensation in buttocks or genitals due to the amount of pain they are experiencing. They may also see it as a sign of improvement in pain.

Pronin et al (2020) indicated a considerable lack of awareness and questioning around sexual dysfunction in a small, single-centre audit. Despite conducting an awareness of the need to ask about sexual dysfunction in suspicion of CES, they still found poor documentation among clinicians on asking this question despite its potential devastating consequences. This was attributed to sociocultural barriers, and lack of initiative to ask or report due to its sensitive nature.

Consideration of CES signs were sought from the past medical, drug, and family history, alongside psychosocial and significant risk factors. Greenhalgh et al (2018) discusses the importance of previous medical and surgical history, as disc prolapses, stenosis, malignancy, and other co-morbidities, such as multiple sclerosis, can mimic CES. Mayo and Herdman (2020) highlight that acute aortic thrombus and pelvic masses also imitate CES. The case study patient reported a strong psychological history, involving domestic abuse, which according to UKSSB (2020) needs consideration when suspecting CES. Previous physical violence and abuse should not be ignored, as the patient may have sustained previous injuries that may not be divulged due to the sensitive subject. A literature search was conducted with key words of CES, and physical abuse/domestic violence; however, no articles were found. It is worth noting that history of physical abuse and depression can alter perception of pain, either by increasing or decreasing the sensitivity (Swift, 2018).

Certain medications can mask CES symptoms. For example, the patient was taking an antidepressant which can alter pain perception due to neurotransmission blocking. Long-term use of lamotrigine can lead to osteoporosis, which is a risk factor for developing CES (Meier and Kraenzlin, 2011). Ibuprofen can increase the likelihood of urinary retention due to renal toxicity (Greenhalgh et al, 2018). No correlations with smoking or amphetamines use with CES were found.

There was little evidence found regarding the incidence of CES after labour. Jones et al (2015) hypothesised difficulty of diagnosing CES due to the presentation, and expectancy of pain and bowel/bladder incontinence after birth.

Clinical examination

Following history-taking a clinical examination took place, involving vital signs. Slightly raised respiratory and heart rate were demonstrated, supporting the patient's complaints of severe LBP (Swift, 2018). A physical assessment using the MSK system, look, feel, move process was conducted (Innes et al, 2018). Greenhalgh et al (2018) negates the need for full neurological examination due to the potential sensory symptoms common in CES. Higginson et al (2020) advises bladder palpation, and/or bladder scanning, may aid confirmation of urinary retention, although bladder scanning is not usually available in primary care.

Quaile (2019) prioritised the need to assess saddle anaesthesia, and anal tone via digital rectal examination (DRE), with Greenhalgh at el (2018) adding the need for clinicians undertaking such examination to be adequately trained, and mindful of having a chaperone due to its sensitive, and invasive, nature. DRE is, however, disputed by several authors including Pronin et al (2020). UKSSB (2020) state that DRE is a poor indicator of CES alone. NICE (2020) advise to consider anal tone, although not to perform DRE in the primary care setting. Long et al (2020) suggested that the anal wink test is more appropriate, and less invasive.

Lower limb weakness or radiculopathy assessment, including reflexes, is recommended by Greenhalgh et al (2018). The patient was found to have a reduced SLR unilaterally of the left leg. Khot and Polmear (2006) evaluate reduced SLR as a highly sensitive indication of nerve root compression. This is supported by Kinirons and Ellis (2005), who add this alongside limb pain as possible CES signs. Diminished reflexes are discussed by Long et al (2020) indicating patella, achilles, and bulbocavernosus reflexes directly represent L4, S1, and S2-4 regions.

On evaluation of the symptoms in the case study, it became apparent that there was a diagnosis of sciatica. However, with the additional neurological symptoms demonstrated, based on the current evidence it would be neglectful to ignore the red flags indicating CES. UKSSB (2020) strongly oppose the neglect of such findings, requiring a good documented reason for lack of referral for immediate MRI.

Differential diagnoses

Differential diagnoses included disc herniation, spinal abscess, tumour, infection, fracture or stenosis. However, Finucane et al (2020) highlight abscess or tumours may incur nighttime sweating symptoms, and fracture or stenosis tend to present in the older population, thus not fitting the case study. All differentials above require further specialist management including MRI. They are also all precursors to CES (Greenhalgh et al, 2018). With limited time, resources, and specialist expertise in primary care, it is therefore essential to refer the patient in a time-critical manner, for appropriate investigation and management, via discussion with the spinal team and admission to A&E (Eames, 2020).

Emergency referral pathways were discussed in the literature, emphasising timing and presentation of key symptoms being precursors for immediate referral (Eames, 2020). These pathways vary regionally dependent on local agreement; however, should involve MRI as gold standard, (UKSSB, 2020). Greenhalgh et al (2018) places importance on all clinicians, including the relatively new role of primary care ANPs, being responsible for their knowledge and awareness of CES. This is especially advantageous in primary care, as exposure to the condition is low.

Communication

Communication is essential, requiring a patient-focused and unambiguous approach, with succinct documentation essential when referring to the spinal team or A&E, reducing any delay in surgical intervention. As Pronin et al (2020) found, poor communication with either patients or colleagues can lead to inappropriate management of CES. To combat this, Greenhalgh et al (2018) and Finucane et al (2020) suggest all patients with LBP be given written cue/credit cards, highlighting the above symptoms for safety netting. Reassuring the patient of the rationale, to avoid further reluctance or delay of treatment (Eames, 2020).

Diagnosis of CES

After a detailed clinical history, MSK, and neurological examination of the case study patient; severe LBP, with unilateral sciatica, bladder/bowel incontinence, saddle anaesthesia, and reduced SLR, with absent reflexes of knee and achilles, were found. The above symptoms were identified as potential CES signs, alongside other less urgent diagnoses. Due to the high risk of missed or delayed diagnosis of CES discussed in this article, the patient was referred to A&E for MRI, as per current guidelines (NICE, 2020). An incomplete L4/L5 disc prolapse was found, and operated on within 12 hours.

Although documented as a rare condition found in primary care, CES is a devastating and disabling condition for the patient, with potential long-term effects, that can be identified earlier as found in this case study (Greenhalgh et al, 2018). Colleagues across primary care, including nurses and ANPs, should be aware of the potential presentation as above, and the value of a thorough, and evidenced-based approach to the physical examination of a patient presenting with sudden onset of LBP and sciatica (Finucane et al, 2020). Additionally, ensuring that patients are encouraged to discuss sensitive information using clear language that could aid diagnosis is also recommended, thus leading to an appropriate and accurate referral (Pronin, et al 2020).

Conclusion

CES is a time-critical condition requiring emergency spinal decompression surgery. It is paramount that a thorough clinical history and examination is undertaken in primary care (NICE, 2020). Due to its complexity in symptomology and presentation, ANPs need to engage in careful questioning and assessment using current clinically recognised red flags (Finucane et al, 2020). There should be a low threshold for referring for immediate MRI scan when LBP with sciatica, bladder/bowel dysfunction, and/or saddle anesthesia are present (UKSSB, 2020).

KEY POINTS:

• CES is a rare and challenging condition to diagnose
• All patients with acute or deteriorating back (+/- radicular) pain should be assessed for CES in primary care
• CES is a time-critical condition requiring emergency spinal decompression surgery
• Red flags to consider are lower back pain with sciatica, bladder/bowel dysfunction, and/or saddle anaesthesia present

CPD reflective practice:

• Why is cauda equina syndrome (CES) time critical to diagnose?
• There is a huge financial burden linked to the diagnosis of CES. Why is this the case and how can you mitigate this risk?
• What are the risk factors for CES?
• What are the pyscho-social implications to consider?
• What would you communicate to your patient if you consider CES a possible differential?