BACKGROUND
Back pain is common in primary care. A practice with a population of 10 000 patients will have 610 patients (6% of the practice population) consulting per year, and while poor outcomes are common (around 60% will still suffer pain at 12 months) GPs need to remain vigilant and actively consider more sinister complications.
Cauda equina syndrome (CES) is a nasty complication of disc herniation, and sometimes, low back surgery, and rarely spinal tumours (both primary or secondary). While this may be considered a rare condition, Hospital Episode Statistics (HES) data recorded 800 CES related operations in England in 2010–2011.1 It is one of the major causes of litigation in the NHS, both for primary and secondary care. This is not surprising, as a previously fit individual is rendered, in various combinations, and often in perpetuity, incontinent of urine and faeces, with loss of perineal, penile, and vaginal sensation, and major disturbance of sexual function. Self-catheterisation, chronic back and leg pain are often added in to the mix.2
TYPES OF CAUDA EQUINA SYNDROME
There are two main types of CES: CES-R and CES-I. R is for retention, where there is established retention of urine, and I is for incomplete, where there is reduced urinary sensation, loss of desire to void or a poor stream, but no established retention and overflow. Both need immediate referral for urgent surgery, but CES-R is less likely to be reversible. In CES-I, the time window from onset of cauda equina symptoms to surgical decompression should be <48 hours (some say 24 hours) to have a reasonable chance of reversal. In practice it is not as simple as this. Some slow onset cases reverse after longer delays, but from the legal point of view, these times are widely accepted criteria. CES-R with retention and overflow may not be identified for what it is by patients and their doctors, making careful questioning and clarification of responses essential. Even if it is suspected, the patient may have reached this stage via CES-I. There may be reasonable grounds for complaint for not spotting this process sooner or failure to warn. It is helpful to record when symptoms and signs first started, as this has management and medico-legal implications.
ANATOMY OF CAUDA EQUINA
The spinal cord terminates at L1. Below this emerges a ‘horse’s tail’ of rootlets (hence its name) that supply not only the lower limbs, but also bladder, bowel and sexual functions. A critical feature of CES is the loss of perineal sensation, unilateral or bilateral. Loss of sensation may be first noticed when cleaning the perineum after voiding or defaecation. In trying to prevent CES, it is reasonable to warn patients with disc herniation to look out for this symptom and to report any disturbance of normal urinary function. Highlighting this in any written patient information provides a useful prompt to patients. This may precipitate inappropriate attendances, but it is probably better to err on the side of safety. As is so often the case, the GP is damned if they do and damned if they don’t warn. Other risk factors are not well established. If the patient has already had a scan showing a developmentally narrow vertebral canal, then even a small disc prolapse can threaten the cauda equina. In most cases there is a massive lumbar disc prolapse that fills a normal sized vertebral canal, compressing the rootlets of the cauda equina. CES can occur in people with a long history of recurrent disc prolapse when a further and larger prolapse occurs. GP’s have been caught out by cries of despair from a patient with a long history of disc prolapse without CES or with an excessive ‘out of hours’ complaint record. There is some evidence that obesity is a risk factor for CES.3 The question ‘can you feel your bottom when you wipe yourself?’ is a useful screening that is easily incorporated into the back pain consultation. A specific change in bladder function relating to the evolution of back and leg symptoms is another. Many patients have a significant increase in back pain with CES. Some get relief from sitting up (presumably because flexion of the lumbar spine widens the vertebral canal).
Intimate examinations are not always practical in primary care settings, but if perineal sensation is tested, then the sharp end of an unravelled paperclip is a useful tool, and better tolerated than a disposable needle or cotton wool. Make sure both sides are tested and results documented.
If a rectal examination is performed, it may be misleading because tone is maintained in CES-I. Recent work with a model suggests that most doctors are not good at assessing degrees of anal tone, so we should not be reassured that all is well if the anal tone seems strong.4 These findings should be recorded, and these findings, positive or negative, are critical for later management of the patients and of establishing your good practice.
MRI SCANS AND CES
The only way to exclude the diagnosis of CES is get an emergency MRI scan, which may not be available to many clinicians working in primary care, especially outside of routine working hours. About 40% of requested scans show no evidence of cauda equina compression. The syndrome is then attributed to uncontrolled back pain. Expert secondary care clinicians cannot definitively confirm or deny a CES diagnosis without MRI, and so why should any other sort of doctor? Unfortunately the record of A&E departments is not good at spotting CES either; even when an experienced GP has made it clear that they suspect CES. Probably the only way to improve diagnosis is to improve access to out of hours MRI scanning. The National Spinal Task Force has made it clear that this service has to be improved1 and access to out-of-hours MRI scanning should be available to all relevant clinicians.
Management and treatment is delivered by specialist spine surgeons, neurosurgical or orthopaedic surgeons. The technical aspects of decompressive surgery range from very easy to highly challenging. The pleasure of relieving prolonged symptoms in one patient is contrasted with the next where rapid surgery is followed by a disappointing outcome. If the CES persists, then there are units and consultants who specialise in the management of chronic CES, and it is worth seeking these out to help these most unhappy patients.
GPs care for large numbers of patients with back pain, the majority of whom will not be at risk of CES. Despite this being a relatively unusual diagnosis, a key message is that this diagnosis has to be considered in all patients with severe back and leg pain (for example, particularly if the back pain is deteriorating and when there may be bilateral leg pain, and loss of perineal sensation is uni- or bi-lateral). Do not be fooled by the patient who prefers to sit up. This condition can easily mislead.
BACK PAIN SERVICES FOR CES
The current organisation of services for patients with CES is problematic, and makes timely and accurate diagnosis challenging. Anecdotal evidence suggests this is a bigger problem in the UK than in countries with similar healthcare systems. An example is New Zealand where, in a publicly-funded health system, CES is not seen as a major litigation problem (personal communication, 2011). In the UK it is difficult to acquire data on CES Litigation.2 There are no easily accessed international comparisons of litigation rates. The causes of these problems are speculative, but experience as an expert in nearly 50 CES litigation cases, suggests that barriers between primary and secondary care, and treatment delays in secondary care seem the most frequent factors, highlighting the importance of heightened awareness and careful assessment of patients in general practice.
Notes
Provenance
Commissioned; not externally peer reviewed.
Competing interests
The authors have declared no competing interests.
- © British Journal of General Practice 2014