From the Guidelines
For patients with a low suspicion of cauda equina syndrome, a combination of thorough neurological examination, post-void residual bladder volume measurement, and serial examinations over time can be used to rule out the condition, with MRI remaining the gold standard for diagnosis if suspicion increases. When evaluating patients with low back pain and suspected cauda equina syndrome, it is crucial to consider the rarity of CES and its potential causes, including lumbar disc herniation, neoplasm, infection/inflammation, spinal stenosis, and hemorrhage 1. A thorough neurological examination is essential, focusing on symptoms such as lower extremity strength, sensation in the perineal region, anal tone, and reflexes, as these can indicate the presence of CES 1.
In terms of alternative exams, the following can be considered:
- Post-void residual bladder volume measurement using ultrasound, with volumes less than 100-150 mL typically arguing against CES
- Plain radiographs to identify obvious structural abnormalities, although these cannot definitively exclude CES
- Laboratory tests, including complete blood count, C-reactive protein, and erythrocyte sedimentation rate, to help identify inflammatory causes of symptoms
- Serial examinations over several hours, which can be particularly useful in low-risk patients, as stable or improving neurological findings suggest against evolving CES
It is also important to note that CT lumbar spine without IV contrast can answer the question of whether or not cauda equina compression is present, and CT myelography of the lumbar spine can assess the patency of the spinal canal/thecal sac and of the subarticular recesses and neural foramen 1. However, MRI lumbar spine without IV contrast remains the most useful initial study for evaluating suspected CES, multifocal deficit, or progressive neurologic deficit, due to its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency 1.
From the Research
Alternative Exams to Rule Out Cauda Equina Syndrome
To rule out cauda equina syndrome in patients with a low suspicion of the condition, several alternative exams can be utilized, including imaging, laboratory tests, and physical examination tests. The following are some of the alternatives:
- Imaging Tests:
- MRI scans: Although MRI is considered the gold standard for diagnosing cauda equina syndrome, studies have shown that other imaging modalities can be used to rule out the condition 2, 3.
- CT scans: CT scans can be used to detect significant spinal stenosis and cauda equina impingement, with high sensitivity and negative predictive value 3.
- MR neurography: This imaging modality can be used to evaluate the lumbosacral spine and detect nerve root damage in patients with suspected chronic cauda equina syndrome 4.
- Physical Examination Tests:
- Bulbocavernosus reflex (BCR): This reflex has been shown to have high sensitivity and specificity for diagnosing cauda equina syndrome 5.
- Rectal tone: This examination finding has been shown to have moderate sensitivity and specificity for diagnosing cauda equina syndrome 5.
- Postvoid residual bladder: This test can be used to evaluate urinary retention and has been shown to have moderate sensitivity and specificity for diagnosing cauda equina syndrome 5.
- Perianal sensation: This examination finding has been shown to have moderate sensitivity and specificity for diagnosing cauda equina syndrome 5.
- Laboratory Tests:
- No specific laboratory tests have been identified as alternative exams to rule out cauda equina syndrome. However, laboratory tests may be used to rule out other conditions that may present with similar symptoms.
Reducing Waiting Times for MRI Scans
To reduce waiting times for MRI scans, the presence of an orthopaedic doctor in the emergency department can be beneficial 6. This can lead to more efficient management of patients with suspected cauda equina syndrome, reducing waiting times for MRI scans and unnecessary inpatient stays.