Case study: cauda equina

Introduction 

Cauda equina syndrome (CES) is a rare condition in which the nerves at the base of the spine become compressed, potentially leading to permanent loss of function. It is diagnosed in <1% of patients presenting to an emergency department with back pain. The condition is often caused by a prolapsed disc in the spine and may require emergency surgery. Other causes include tumours, infections, stenosis of the spine (particularly in the elderly), haematoma, inflammation and vascular changes. The clinical presentation is variable and is characterised by a broad range of symptoms and signs, some of which, such as low back pain and sciatica, are relatively common and not specific to CES.  

Thus, diagnosis can be challenging, and the condition is normally confirmed by magnetic resonance imaging (MRI) scans. One major drawback of MRI is that it is not always available in an emergency that arises out-of-hours, particularly in smaller regional hospitals. Furthermore, classification of the findings from MRI is difficult, as many different terminologies and phrases may be used to describe identical pathology.  

Studies have indicated that only around 50% of MRI scans of patients with suspected CES demonstrate pathology indicating impingement or disc prolapse, a situation which may require emergency discectomy. In addition, it is not uncommon to see severe compression of the cauda equina with no symptoms whatsoever. Patients without impingement still require urgent management, but they do not need to be treated as an emergency. Therefore, both MRI and surgery could be deferred in these patients until the next available list. The challenge lies in identifying which patients are emergencies and which are not. Given the serious consequences of a missed or delayed diagnosis, most clinicians opt for MRI as a matter of course.  

The patient’s history and findings on clinical examination are rarely enough to definitively diagnose CES. Symptoms such as urinary retention, urinary frequency, incontinence, altered urinary sensation and altered perineal sensation are only accurate in diagnosing CES in around 60% of cases. However, a combination of findings from physical examination, such as rectal tone, perianal sensation and bulbocavernosus reflex, do provide an effective means of excluding a diagnosis of CES.  

Current national guidelines in the UK state that all patients with suspected CES should undergo an MRI prior to referral to a specialist spinal unit, and surgery should be performed as soon as possible. It is evident that while not all cases require treatment as an emergency, most patients need to be treated urgently.  

Sciatica is a common condition, characterised by radiating leg pain, which may lead to disability. The annual prevalence in the general population is around 2.2%. In the majority of cases, sciatica is caused by a herniated disc that leads to nerve root compression. Lumbar stenoses and tumours are less common causes. Sciatica is mainly diagnosed through history taking and physical examination, which usually consists of neurological testing. Unless there are red flags indicating the presence of underlying disease rather than disc herniation, imaging is not generally helpful. Patients are usually treated conservatively in primary care, but in the small proportion of patients whose symptoms do not resolve after a few weeks, referral to secondary care and possible surgery may be necessary. Sciatica alone does not fulfil the requirement for the diagnosis of CES, nor does it necessitate an MRI scan to exclude compression of the central nerves.  

Case Presentation 

Patient history and demographics 

In late November 2022, Patient A, a man of undisclosed age, woke with numbness and loss of sensation in his lower right-hand side and was unable to walk. His bladder and bowel movements were also extremely infrequent. He was taken to hospital by ambulance, where he was examined by a nurse, who diagnosed sciatica and advised that no treatment could be provided. Pin prick tests and a rectal examination were not performed. He was not seen by a doctor and was discharged home. The patient’s symptoms did not improve and three days later, Patient A returned to hospital where an x-ray was carried out. This showed nothing of concern, and he was discharged home.  

Patient A’s symptoms failed to resolve, and in December an MRI scan was arranged. This showed a prolapsed disc at L4-5, causing severe nerve compression. An annular tear at the level of L5/S1 was also identified, but this was not associated with a significant amount of compression. Patient A was advised that urgent surgery may be required, that he was being treated for cauda equina syndrome (CES) and that he needed to be transferred to another hospital for the surgery, but this did not happen due to bed availability. His notes should have been sent to another hospital so that his case could be discussed regarding surgery, but this did not happen, and he had no further contact from the hospital. A review of the MRI scan determined that the location of the compression removed the need for urgent surgery.   

Several days later, Patient A was told by the consultant that as he had now missed the 48-hour window from the onset of symptoms, surgery would not take place for 4-6 weeks. By this stage, he had not had a bowel movement for 13 days and was struggling to urinate. He was also experiencing increasing numbness in both sides of his body.  

In January 2023, Patient A was advised by his consultant that he required a serious operation, from which long-term nerve damage was a possible consequence. The surgery, which consisted of L4/5 decompression and a right L4/5 microdiscectomy, took place in late February, after which most of the pain symptoms resolved. However, some residual nerve damage to the big toe remains which causes issues with balance, walking and driving. Patient A also suffers with urinary and bowel urgency and erectile dysfunction, which may also be the result of nerve damage.  

Patient A’s medical records show a long history of pain related symptoms, dating back over several decades and he has previously received physiotherapy treatment for neck and back pain. His medical records evidence possible disc damage following an episode of low back pain ten years prior to the index event, and some degenerative changes had been noted. In the months preceding the index events, Patient A had complained of worsening back pain, which had been present intermittently for several years. In August 2022 he reported a year-long history of erectile dysfunction. A diagnosis of sciatica was given; these symptoms did not respond to analgesics or physiotherapy. The patient was advised of the symptoms of CES and told to attend accident and emergency should they occur.  

Treatment and management 

Patient A has been prescribed a variety of analgesics for his pain symptoms, including naproxen, gabapentin, amitriptyline and diazepam, although none has offered full relief of symptoms. Since the index events, he has been prescribed oramorph and diclofenac, along with medication for his constipation. His erectile dysfunction has been treated with sildenafil, which was partially effective. He has also received several rounds of physiotherapy treatment.  

Legal aspects related to the case 

Although loss of sexual function is a known risk of decompression surgery, it is not included as a complication of this surgery in the patient booklet supplied by the British Association of Spinal Surgeons and is often overlooked during the informed consent process. This appears to be the case with Patient A. Bladder/bowel dysfunction and paralysis were included on the informed consent form.  

The assumption about the causality of Patient A’s urinary incontinence being due to factors other than cauda equina compression should only have been made in hindsight and not at the time of presentation.  

The failure to perform an MRI scan in patient A, who was presenting with sciatica and bladder dysfunction, represents a breach of duty. Rectal examinations are commonly conducted during assessment for cauda equina. However, the examination that was carried out may have been unnecessary if urinary incontinence was not present.  

By January 2023, there was no evidence of irreversible compression of the cauda equina and urgent surgery was not required. Therefore, it does not constitute a breach of duty not to offer surgery.  

The cause of Patient A’s incontinence depends on the timing of onset. If it occurred immediately after surgery, it is a complication of surgery for which he was consented. There has been no increase in this risk due to the delay in performing the surgery. If the abnormal bladder function occurred at the time of the index events in November 2022, on balance of probabilities, early decompression would have given a better resolution of symptoms. However, entries in the patient’s medical records in January 2023 indicate that bladder function had returned to normal.  

Expert opinion 

Causation 

Patient A’s pain and disability resulting from his prolapsed disc appeared to be profound and would be an indication for early intervention. It seems unlikely that his pre-operative erectile dysfunction was related to the disc prolapse. However, the worsening of this symptom after decompression surgery is consistent with damage to the relevant nerves during surgery.  

There is some discrepancy in the patient’s medical notes made by the examining nurse and the A&E doctor as to whether urinary incontinence occurred as part of the index events. As this symptom subsequently resolved without treatment, it is unlikely to have occurred due to cauda equina compression and is more likely to be related to the patient’s severe constipation, drug ingestion and pain. Any new bladder symptoms would necessitate investigation. However, it may be considered reasonable to watch and wait if function had returned to normal. 

If the MRI scan had been performed earlier, it would have identified a central disc prolapse at L4/5. Surgery would have been offered on the next available list.  

Conclusion 

Outcome 

Decompression surgery largely resolved the patient’s pain symptoms. Nerve damage sustained during the operation has affected his big toe, and he suffers with urinary and bowel urgency as well as sexual dysfunction.  

Discussion 

Following a long history of pain-related symptoms, Patient A presented at hospital with symptoms that were initially diagnosed and treated as sciatica. An MRI scan was not carried out at this time, but when one was performed some 10 days later, a prolapsed disc and severe nerve compression were identified. Although the patient was informed that urgent surgery may be required, it was not carried out until over 2 months after the initial presentation at hospital. Following surgery, Patient A’s pain symptoms almost completely resolved. Residual symptoms affecting his big toe and causing sexual dysfunction may have been caused by nerve damage sustained during the operation.  

There are discrepancies in the patient’s medical notes regarding the presence or absence of urinary incontinence. Given that this symptom is important in the diagnosis of CES, it may explain the failure to carry out an MRI scan at initial presentation.  

Aspects of this case relating to clinical negligence 

Patient A’s sciatica should have been treated after a short period, usually lasting about 6 weeks, of self-management. If symptoms fail to improve, management should consist of an MRI scan and referral for consideration of injection or decompression surgery. There is no recommended timeline for these interventions, due to the variable nature of sciatica and back pain, although earlier surgical intervention tends to give better results. Patient A’s notes indicate that neurology of the lower limbs was normal, rectal examination was normal and there were no urinary or bowel symptoms. Therefore, decompression was not required but could be considered. Where a patient has recurrent or intermittent symptoms indicative of compression of the cauda equina, it is reasonable to offer a patient decompression surgery, but it is not mandatory to do so.  

Entries in Patient A’s medical notes regarding his episodes of back pain and sciatica should have been sufficient to consider screening for cauda equina. Bilateral sciatica is normally considered a red-flag symptom that necessitates an MRI scan. Furthermore, evidence of urinary incontinence should also have indicated that an MRI was necessary. CES guidelines dictate that scanning should be performed as soon as possible once a clinical diagnosis has been established. A bladder scan is not required, although it can assist in assessing post-voiding residual bladder volume, the results of which may indicate an MRI is needed.  

In this case, true cauda equina could have occurred at any time, particularly in December 2022 when the patient presented with bilateral sciatica and altered bladder function. Surgery should have been offered at this timepoint. However, by January 2023 there was no evidence of irreversible compression and urgent surgery was not required. It would however be reasonable to discuss surgery for the treatment of pain.  

Patient A was not consented for loss of sexual function following decompression surgery even though it is a known risk of this type of surgery. To enable a patient to give proper informed consent, it is vital that every known risk, however unlikely, is discussed during the consenting process.  

This case demonstrates the difficulty in diagnosing CES, particularly when there appear to be discrepancies in the patient’s medical notes. It also demonstrates the importance of adhering to clinical guidelines regarding the diagnosis of CES, especially with respect to the need for MRI imaging.