From the Guidelines
Diagnosing cauda equina and conus medullaris syndromes requires a systematic approach beginning with a thorough history and physical examination, with urgent magnetic resonance imaging (MRI) of the lumbosacral spine being the gold standard imaging modality. Clinicians should inquire about saddle anesthesia, bowel or bladder dysfunction, bilateral leg weakness or numbness, and recent back pain or trauma. The physical examination should assess lower extremity strength, sensation (particularly in the perianal region), deep tendon reflexes, and rectal tone. A digital rectal examination is essential to evaluate anal sphincter tone and voluntary contraction. Postvoid residual bladder volume should be measured, with volumes exceeding 100-200 mL suggesting urinary retention.
Some key points to consider in the diagnosis of cauda equina and conus medullaris syndromes include:
- The most common cause of cauda equina syndrome is lumbar disc herniation at the L4-L5 and L5-S1 levels, as noted in the study by Fairbank et al 1.
- MRI lumbar spine without IV contrast is most useful in the evaluation of suspected cauda equina syndrome, multifocal deficit, or progressive neurologic deficit because of its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency, as recommended by Bell et al 1.
- Although MRI is superior in soft-tissue contrast and characterizing the etiology of cauda equina syndrome, CT lumbar spine without IV contrast can answer the question of whether or not cauda equina compression is present, as shown in a recent retrospective review of 151 patients with clinically suspected cauda equina syndrome 1.
- CT myelography of the lumbar spine assesses the patency of the spinal canal/thecal sac and of the subarticular recesses and neural foramen, and can be useful for surgical planning in patients with cauda equina syndrome and in patients with significant spinal stenosis on CT lumbar spine without IV contrast, as noted in the study by Bell et al 1.
These syndromes constitute medical emergencies requiring prompt diagnosis, as surgical decompression within 48 hours of symptom onset offers the best chance for neurological recovery, particularly for compressive lesions like disc herniations or tumors. Laboratory tests including complete blood count, inflammatory markers, and urinalysis may help identify infectious causes.
In terms of specific diagnostic steps, the following should be considered:
- A thorough history and physical examination to identify symptoms and signs of cauda equina or conus medullaris syndrome
- Urgent MRI of the lumbosacral spine to visualize the conus medullaris, cauda equina, and potential compressive lesions
- Measurement of postvoid residual bladder volume to assess for urinary retention
- Digital rectal examination to evaluate anal sphincter tone and voluntary contraction
- Laboratory tests to identify infectious causes, as recommended by the American College of Physicians and the American Pain Society 1.
From the Research
Diagnostic Steps for Cauda Equina and Conus Medullaris Syndromes
The diagnostic steps for cauda equina and conus medullaris syndromes involve a combination of clinical evaluation, imaging studies, and sometimes, urgent surgical intervention. The key symptoms to look out for include:
- Back pain
- Unilateral or bilateral leg pain
- Paresthesias and weakness
- Perineum or saddle anesthesia
- Rectal and/or urinary incontinence or dysfunction 2
Clinical Evaluation
A thorough history and physical exam are crucial in diagnosing cauda equina syndrome (CES) and conus medullaris syndrome (CMS) 3. The clinical examination may not be sensitive enough to exclude CES, emphasizing the need for urgent imaging studies in suspected cases 4.
Imaging Studies
Magnetic resonance imaging (MRI) is the preferred imaging modality for diagnosing CES and CMS 4, 3. Computed tomography (CT) myelogram can also be used to aid in diagnosis and treatment 3. MRI findings may include compression of the nerve roots at the spinal cord's terminus, and in some cases, enhancement of nerve roots may indicate a breakdown of the blood-nerve barrier, as seen in Guillain-Barré syndrome 5.
Classification and Treatment
The Lavy et al classification system can be used to categorize different types of CES 4. Surgical decompression is the definitive treatment for CES and CMS, with recommendations for urgent surgery within 48 hours, preferably within less than 24 hours 4. However, the timing of decompression remains debated, with some studies reporting no significant difference in outcomes between decompression within 24 hours vs. 48 hours 6.
Importance of Early Diagnosis and Treatment
Early diagnosis and treatment are crucial for optimal outcomes in CES and CMS 3, 6. Delayed diagnosis can lead to significant morbidity and potential legal implications for physicians 6. Therefore, it is essential for healthcare providers to be aware of the severity of these conditions and to prioritize timely diagnosis and treatment.