Recommendations
Key Recommendations
Suspect cauda equina syndrome (CES) if a patient presents with leg pain and/or back pain together with recent onset (<14 days), or deterioration, of any of the following red-flag symptoms:[14][15][16][17][18]
Disturbance of bladder or bowel function. Sensory changes are particularly significant.
Altered sensation (e.g., numbness or pins and needles) around the perianal, perineal, or genital ('saddle') areas.
Motor weakness or other neurological deficits affecting both legs.
Sexual dysfunction.
If suspected CES presents in the community, make an immediate referral to hospital, to be seen within a few hours or sooner if possible.[19] This should be to a hospital that has emergency, round-the-clock provision of magnetic resonance imaging (MRI) if at all possible.[15][16]
If a patient presents at hospital with suspected CES, arrange an emergency MRI scan of the lumbosacral spine; this should be performed as soon as possible and certainly within 4 hours of the request.[15] Perform a pre- and post-void bladder scan (but only if this will not cause a delay in proceeding to MRI scanning).
A post-void residual volume (PVR) ≥200 mL makes CES significantly more likely, but PVR <200 mL does not exclude it.[15][20][21][22]
Note that a digital rectal examination is not required to meet the index of suspicion to justify emergency MRI.[14][23]
Confirmation of a CES diagnosis depends on the combination of cauda equina compression detected on MRI together with the presence of one or more red-flag symptoms or signs.[1][4]
If CES is confirmed, make an immediate referral, day or night, for emergency spinal decompression surgery.[15][16][17]
CES is a spinal surgical emergency that must be diagnosed and treated in a time-critical manner to ensure the best possible outcome.[15]
Recognition of early symptoms and signs is paramount so that treatment can be initiated before CES progresses to cause irreversible damage.[1][8][14] This can be challenging as many of the early symptoms and signs may be subtle and non-specific.
Delays in diagnosis and/or surgical treatment can result in permanent, life-changing motor and sensory disabilities including lower limb paralysis and loss of bladder, bowel, and sexual function.[15][16][24][25]
Suspect CES in any patient who presents with leg pain and/or back pain together with recent onset of (<14 days), or deterioration of, any one or more of the following red-flag symptoms:[14][15][16][17][18]
Disturbance of bladder function: for example, difficulty starting or stopping urinary flow; impaired sensation of urinary flow; urinary retention and/or overflow urinary incontinence (an indicator of late-stage, or severe, potentially irreversible CES).
Disturbance of bowel function: for example, loss of sensation of rectal fullness; changed sensation when passing a bowel movement; loss of anal sphincter tone; faecal incontinence (an indicator of late-stage, potentially irreversible CES).
Altered sensation (e.g., numbness) around the perianal, perineal, or genital ('saddle') areas (S2-S5 dermatomes). This may be subjectively reported by the patient or objectively identified on examination.
Severe or progressive neurological deficits affecting both legs: for example, major motor weakness of foot dorsiflexion, ankle eversion, or knee extension.
Sexual dysfunction: for example, inability to achieve erection or ejaculate, or loss of genital sensation.
It is vital to focus on identifying the early features of CES as this is the group of patients with most to gain from time-critical surgical intervention. Such patients may have only subtle neurological symptoms and/or signs.[23]
It has been argued that true red flags are the symptoms and signs that warn of further, avoidable damage, and that symptoms and signs of late, irreversible CES (e.g., painless urinary retention or faecal incontinence) could be more accurately described as 'white' rather than 'red' flags.[26]
Practical tip
Be aware that CES does not develop according to a predictable pattern, and presentation varies widely between patients.
If a patient with symptoms of suspected CES presents in the community, make an immediate referral to hospital (to be seen within a few hours or sooner if possible), in line with local pathways.[19]
Under the NHS England national pathway for CES, the immediate referral should be to a hospital that has emergency (ideally round-the-clock) provision of magnetic resonance imaging (MRI).[15][16] NHS England, Getting It Right First Time: national suspected cauda equina interactive pathway Opens in new window
If a face-to-face assessment is not possible or will delay referral, make an emergency referral based on identification of CES symptoms during a telephone assessment.[15]
Do not request any community-based investigations. The priority is immediate referral to a hospital with emergency MRI provision.
If a patient presents in a hospital setting with recent-onset (<14 days) or deteriorating symptoms of CES, arrange emergency MRI as soon as possible. Perform a pre- and post-void bladder scan (as long as this will not delay the MRI scan).[15]
Confirmation of a CES diagnosis depends on the combination of red-flag symptoms and/or signs together with a positive finding of cauda equina compression on MRI.[1][4] There is no single symptom or sign (or combination) that reliably confirms or excludes CES, hence emergency MRI is essential in all suspected cases.[1][9][27][28][29] Conversely, an MRI scan on its own cannot diagnose CES; typical symptoms and/or signs must also be present.[15]
The reliability of clinical diagnosis is low. Each individual red flag symptom/sign has a low positive predictive value and, at best, only moderate specificity for CES.[14][15][16][18][24]
Negative examination findings cannot exclude CES if subjective red-flag symptoms are present.[14][15][23] A low threshold is therefore paramount for requesting an emergency MRI for any patient who reports red-flag symptoms, regardless of the absence of relevant signs on examination.[15]
Urgent referral for bilateral sciatica or for stable CES symptoms >14 days' duration
Make an urgent referral to the musculoskeletal medicine service (to be seen within 2 weeks) if a patient presents with either of the following:[14][15]
Red-flag CES symptoms that have been present for >14 days but are completely stable and non-deteriorating.[15] In this scenario, the urgency of MRI is at the discretion of the specialist clinician.[15]
OR
Sudden-onset bilateral radicular pain or radicular pain that started unilaterally but has progressed to bilateral but without any red-flag symptoms or signs of CES. Bilateral radicular pain (i.e., sciatica pain that radiates from the lower back to the buttock and leg) can be a warning symptom that CES may occur.[14][15][16] Document the duration, frequency, and progression of the bilateral radicular pain.[15]
Ensure that all such patients are advised to return for immediate re-assessment if any of their symptoms worsen or any new CES symptom develops.[14] If this occurs, emergency referral for an immediate MRI (day or night) is warranted.[1][15]
Provide safety-netting advice, in patient-appropriate language, highlighting the importance of seeking immediate hospital assessment for possible CES if the patient develops any one or more of the following while waiting for the urgent referral appointment:
Loss of feeling or pins and needles affecting the inner thighs or genitals
Numbness in or around the back passage or buttocks
Altered sensations when using toilet paper
Difficulty trying to urinate or trying to stop or control the flow of urine
Loss of sensation when passing urine
Not knowing whether the bladder is full or empty
Inability to stop a bowel movement happening, or leaking of faeces
Loss of sensation when passing a bowel motion
Loss of genital sensation during sexual intercourse
Practical tip
Warning cards and videos aimed at patients are available for safety-netting. Examples include a video and card (available in multiple languages) produced by the UK Musculoskeletal Association of Chartered Physiotherapists. NHS/MACP: cauda equina syndrome Opens in new window
Practical tip
Most patients who have unilateral radicular pain without any red-flag features of CES do not require MRI. The natural history of most cases of nerve root pain is gradual improvement with time.[23]
Taking a thorough history is critical to the early diagnosis of CES.[30]
A cohort study of 621 UK patients with CES found that the most frequent presenting symptoms were back pain (96%), sciatica (93%), bladder dysfunction (83%), and saddle numbness (81%). Bowel dysfunction (39%) and sexual dysfunction (38%) were less commonly reported.[22]
If a patient presents with acute or deteriorating radicular pain (i.e., sciatica-type pain that radiates from the lower back to the buttock and leg) and/or back pain, assess for the possibility of CES.[14]
Confirm whether any radicular pain is unilateral or bilateral and stable or progressive.[14]
Bilateral sciatica on its own is a common presentation in primary care and is not necessarily a trigger to suspect CES.[14] More concerning presentations are sudden-onset bilateral sciatica or unilateral sciatica that progresses to become bilateral; as long as there are no red flags for CES that should trigger emergency magnetic resonance imaging (MRI), these patients require urgent referral (to be seen within 2 weeks) by the musculoskeletal medicine service.[14][15] However, the evidence base in this area is limited and of poor quality.[14] It is vital to provide safety-netting advice on CES symptoms to any patient who presents with either acute or chronic bilateral sciatica without any red-flag symptoms.[14]
As part of your assessment for possible CES, ask specifically about the following red-flag symptoms in any patient who presents with sciatica or low back pain:[14][15]
Any changes in perianal, perineal, or genital sensation.
Any change in bladder or bowel function, however minor.[1] In particular, check for any difficulty initiating a flow of urine, impaired sensation of urinary flow or bladder fullness, or loss of sensation of rectal fullness. Note that urinary or faecal incontinence are symptoms of late-stage or severe CES and associated with a worse prognosis.[4]
Any changes in sexual function or sensation. Estimates of the prevalence of sexual dysfunction vary; this is partly because it is often poorly documented.[31][32]
Practical tip
When patients have acute leg pain and/or back pain, they often emphasise this and overlook subtle symptoms of CES such as perineal numbness or early bladder symptoms (e.g., mild changes in urinary sensation, flow, and/or frequency).[4][25]
It is therefore vital to ask very specific, direct questions about the presence or absence of each red-flag symptom, using language the patient understands.
Explain why you are asking these questions as patients are usually not aware of the possible link between back pain and urinary or bowel symptoms.
Practical tip
Urinary dysfunction is very common in older people, making it challenging to distinguish possible CES from other age-related symptoms. Impaired sensation is a strong pointer to consider the possibility of CES. Good discriminatory questions to ask the patient are:
Do you know when you need to pass urine?
Can you stop and start the flow of urine without trouble?
Does it feel normal when you pass urine?
Practical tip
Low back pain with sexual dysfunction as the only other feature is unlikely to be due to CES.[15]
Document the time of onset of each symptom as this may influence the urgency for MRI and the prognosis following spinal surgery.[14][15]
Also record the duration, frequency, and progression of any relevant symptoms.[14]
Be aware of common causes of, and risk factors for, CES:
The most common cause of CES is a large lumbar disc prolapse that compresses the roots of the cauda equina in the lower lumbar spinal canal.[4]
Rarer causes include haematoma, spinal trauma, recent spinal surgery, spinal epidural abscess, and spinal or epidural anaesthetic.[2][6][12][15] For information on malignant causes, see Malignant spinal cord compression.
Risk factors for CES include age <50 years; anticoagulation therapy (which increases the risk of haematoma); and known spinal stenosis (the most common cause of thecal sac compression in older people).[6][14]
Note that CES can occur in patients with long-standing conditions such as lumbar canal stenosis.[7][33][34]
In such patients, it is important to ensure that appropriate attention is paid to any new red-flag symptoms, however subtle, that raise suspicion of CES.
The same criteria can be used as for other patient groups to determine the urgency of referral for imaging.
If CES is suspected in a patient presenting in the community or in hospital, conduct a careful neurological examination with a focus on the legs. Assess:[1][15][23][25]
Reflex changes (ankle, knee, plantar). There may be diminished reflexes depending on the nerve root affected. Bilateral loss of a reflex may indicate compression of nerve roots on both sides.[35]
Tone and presence or absence of clonus.
For any lower limb myotomal weakness.
For any numbness or sensory loss to soft touch or pinprick.
Provocative tests (straight leg raise and femoral nerve stretch test).
For any changes in gait.
Also assess for any soft touch or pinprick sensory loss in the perianal, perineal, and genital areas and the posterior thigh.[1][4][14]
If this is not carried out, document the reason (e.g., no chaperone available).[14]
A cohort study of 621 UK patients with CES found that light-touch saddle sensory examination was normal in 33%, unilaterally abnormal in 32%, and bilaterally abnormal in 37%.[22] Pinprick sensation was normal in 33%, unilaterally abnormal in 35%, and bilaterally abnormal in 32%.
Palpation may reveal a full bladder due to urinary retention, which is a sign of late-stage CES.
A digital rectal examination (DRE) is not necessary for a community-based presentation of suspected CES.[15]
It is important, however, to document the patient's subjective assessment of perianal sensation.
In the hospital setting, a DRE can be considered for assessment of anal tone and presence of voluntary anal contraction, but it is not essential.[14]
The value of DRE in the acute diagnosis of CES has been questioned, and it is not required to meet the index of suspicion that justifies an emergency request for magnetic resonance imaging (MRI).[14][23]
A meta-analysis of six studies involving 741 patients found that the use of DRE had low diagnostic accuracy for detecting CES but did carry a high risk of false reassurance.[36] DRE also has poor inter-observer reliability.[1]
Remember that a normal physical examination does not obviate the need for emergency MRI if the patient has red-flag symptoms for CES.[14][15][23]
Imaging
Emergency imaging is vital for any patient with suspected CES, to ensure minimal delay if decompression surgery is needed. Magnetic resonance imaging (MRI) is the recommended modality for almost all patients, with computed tomography (CT) reserved for individuals with contraindications to MRI.[1][15][16][17]
MRI is the preferred imaging investigation because of its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency.[1][37]
MRI scanning
Arrange an emergency MRI of the lumbosacral spine as the first-line investigation for any patient who presents at or is referred to hospital with red-flag symptoms for suspected CES.[1][6][15][16][18][24][37]
Under the NHS England national pathway for suspected CES:[15]
MRI should be performed as soon as possible and certainly within 4 hours of the request.[15][18]
There is no requirement to discuss the patient with the spinal surgery service prior to the MRI as this may lead to unwarranted delay.[15][16] However, a discussion with a senior decision-maker (ST4 or equivalent or above) is recommended.[15]
If a radiologist is unavailable to report on the scan out of hours, the on-call surgical team can be asked to review it to avoid delay.[15] The UK Royal College of Radiologists' service standards for CES state that the MRI report should be issued within 1 hour of the scan.[18]
A single sagittal T2 weighted sequence is the recommended MRI protocol to screen for cauda equina (CE) compression.[15][18]
If CE compression is identified, additional sequences (axial T2 weighted and sagittal T1 weighted) may be needed to inform the surgical approach.[15][18]
MRI can be used for pregnant patients with suspected CES as long as a critical risk-benefit analysis justifies it, and national safety guidelines are followed to minimise risk to the patient and fetus.[18][38]
The majority of MRI scans for individuals with red flag symptoms and signs are negative for CE compression.[17] It is advisable to make the patient aware of this before they have the scan, as this can help to manage expectations around the likelihood of identifying a specific cause for their symptoms.
One literature review found that rates of positive MRI findings in patients with suspected CES range from 14% to 33%.[1] This is because red-flag symptoms and signs have low specificity for CES and symptoms such as back pain and urinary dysfunction are very common in the general population.[1][22][24] No symptom or sign can reliably diagnose or exclude CES prior to the stage where the lesion is severe and the neurological damage is irreversible.[17] It is therefore vital to maintain a low threshold for requesting emergency scanning despite the low likelihood that it will confirm the diagnosis.[17][25]
Conversely, positive MRI findings must always be interpreted in the context of the full clinical picture. If there is a discrepancy between the physical examination or symptoms versus MRI findings, it is important to remember that the sensitivity of MRI in relation to CES means that it is used to 'rule in' rather than 'rule out' the diagnosis.
Computed tomography (CT)
If there is an absolute contraindication to MRI (e.g., presence of an MR-unsafe implant), request a CT scan or CT myelogram.[15][18] It may be appropriate to consult the spinal surgery team in these circumstances.[16]
CT can delineate whether CE compression is present but is less precise than MRI at characterising the aetiology of CES.[37] Thecal sac effacement of ≥50% has been proposed as a criterion for identifying CES on CT.[39]
CT modalities have poor soft-tissue contrast compared with MRI and so might not reveal disc protrusions in older patients with degenerative spinal conditions.[18]
CT myelography can be used to assess the patency of the spinal canal/thecal sac, and can be useful for surgical planning.[37]
Pre- and post-void bladder scan
A pre- and post-void bladder scan can be a useful adjunct to MRI in assessment of urinary retention and completeness of bladder emptying in a patient with suspected CES.[15][40] It can be undertaken while the patient is waiting for MRI scanning but it must not delay MRI scanning or surgery.[15]
Do not use the results of bladder scanning in isolation to determine whether an MRI is indicated.[15] Every patient with suspected CES requires an emergency MRI, regardless of the findings of a bladder scan.[15][22]
If the patient is able to void, document the pre-void volume and the post-void residual volume (PVR).[15]
PVR ≥200 mL makes CES significantly more likely.[15] A prospective study of 260 patients with suspected CES found that a PVR ≥200 mL had 94% sensitivity and 67% specificity for identifying MRI-positive CES.[20]
PVR <200 mL makes CES less likely but does not exclude it.[15][21] A multi-centre cohort study of 621 UK adults with CES found that 59% of those who had a bladder scan documented had a PVR <200 mL.[22]
If PVR is >600 mL, catheterise the patient. Perform a catheter tug to check whether the patient has sensation.
If imaging confirms cauda equina compression:
Make an immediate referral (day or night) for emergency spinal decompression surgery.[15][16][17]
If this requires transfer to another hospital, the NHS England national pathway for CES recommends transfer via a category 2 blue-light ambulance.[15]
Keep the patient nil by mouth in preparation for surgery.[15]
As soon as a decision to operate has been made, catheterise the patient (if catheter is not already in place).[15]
If there is no CE compression but imaging indicates the presence of neural compression that explains the patient's radicular pain:[15][16]
Provide safety-netting advice about the importance of seeking immediate help should any symptoms of CES develop.
Make a referral to the community musculoskeletal medicine team.
The extent of the patient's neurological deficit at presentation has a significant impact on the prognosis as it reflects the degree of damage to the cauda equina nerves.[1][4][15] It may also be a factor informing the precise urgency of emergency surgery.[23]
It is important to document the degree of neurological deficit: in particular, whether the patient has painless urinary retention and overflow incontinence (which is sometimes referred to as CESR).
Patients who retain some executive control over bladder function (sometimes referred to as incomplete CES or CESI) have a better prognosis than those with painless urinary retention (CESR). Patients with CESI may have altered urinary sensation, a loss of the desire to void, a poor urinary stream, and a need to strain in order to urinate, but voluntary voiding remains possible even if difficult.
Although the prognosis is less positive for patients with CESR, evidence suggests that a significant proportion of this group will benefit from at least some recovery of bladder function following decompression surgery.[22]
It is generally agreed that patients who present with complete CES have a poor prognosis for recovery. Complete CES is characterised by loss of all CE function, absent perineal sensation, a paralysed and insensate bladder and bowel, no perineal or perianal sensation, and a patulous anus.[4]
However, classifying individual patients into subcategories of CES severity is unreliable and requires great caution in clinical practice.[5]
Several groups have proposed that it is important to subcategorise CES patients according to their degree of neurological deficit (for example, suspected CES, early CES, incomplete CES, CES with painless urinary retention, or complete CES).[1]
However, research shows that there is very poor inter-observer agreement between clinicians when asked to determine the most appropriate subcategory of CES for 100 individual patient vignettes.[5]
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