3.5 Cauda equina syndrome

Cauda equina is a well-known but rarely diagnosed condition. Untreated, the consequences of this syndrome for the patient are devastating. Poor results can occur even with expeditious treatment. It is a frequent cause of negligence litigation. It is important that clinicians are aware of its presenting features and the pitfalls surrounding diagnosis. Patients with severe back pain may go into retention because of severe pain without cauda equina syndrome (CES). It is sometimes difficult to distinguish the effects of severe pain from true cauda equina compression. If in doubt seek help and an emergency magnetic resonance scan. If the symptoms are of rapid evolution, this is a surgical emergency. If the onset is slow, it is more difficult, but an early magnetic resonance scan is very helpful in identifying the aetiology. Cauda equina compression can occur when there is a large, and particularly central, disc prolapse in association with a relatively narrow vertebral canal. CES may come on insidiously and incompletely. On other occasions, it may have an acute onset and profound deficit. Other causes of CES include: tumours, both primary and secondary; fractures where the lumbar canal is seriously distorted; infections with epidural pus; and haematomas, either spontaneous or as a complication of spinal surgery.

Some literature suggests that surgery within 24h of onset is likely to be successful (>90% relief of symptoms) whilst surgery after 48h onset is likely to be a failure. It is likely that this is an oversimplification. Gleave and Macfarlane distinguished those patients with retention or retention and overflow (CESR) from those with bladder dysfunction (CESI)—the former do badly even with expeditious surgery. McCarthy and colleagues reviewed a larger series and were not able confirm this distinction. Indeed they were not able to relate time to surgery and outcome at all. Todd has presented evidence that timing does matter. DeLong et al in the largest meta-analysis to date support the distinction of CESI and CESR.

One issue is that it is sometimes difficult to identify when the clock starts ‘ticking’ at the onset of CES. This is important when negligence in diagnosis or treatment is alleged. Many believe that this is when ‘autonomic’ symptoms and signs occur (urinary incontinence or retention). Others will time it from onset of perianal numbness (usually but not always bilateral). In all events the patient should be warned that their recovery of autonomic function may well be imperfect. Most patients will have back pain indefinitely.