Chapter 2. Localization Signs in Neurology
A 38-year-old woman with no significant past medical history presents to the emergency department with acute-onset severe low-back pain that began 2 days ago. There was no antecedent history of trauma. She describes pain in the lower back that radiates to the sole of her right foot. She also recently noticed difficulty raising her right foot from the ground when walking. On further questioning she admits to having less frequent urination recently. Her motor examination revealed weakness in ankle plantar flexion and dorsiflexion on the right side. Knee jerks were normal, but ankle jerks were decreased on both sides. Sensation was intact in both lower extremities, but there was decreased sensation in her right perineum. What is the most likely localization?
(C) Bilateral medial frontal hemispheres
(D) The cauda equina is a combination of lumbar, sacral, and coccygeal nerve roots as they travel down to their respective exit foramina. Because it contains lumbar, sacral, and coccygeal nerve roots, its function includes mediating movement of the lower extremities, sensation to the lower extremities, bladder and external anal sphincter control, sensation to the external genitalia, and sensation overlying the coccyx. The hallmark of cauda equina syndrome is usually radiating low back pain, although it may also present with isolated deficits related to dysfunction of any of the nerve roots in the cauda equina. Other symptoms include urinary incontinence or retention, fecal incontinence or retention, loss of anal sphincter tone, sexual dysfunction, saddle anesthesia, or hypoesthesia. This patient presents with weakness and sensory and reflex changes involving the lower roots, suggesting lower lumbar/sacral involvement. Perineal numbness may be patchy, mild, or unilateral at onset of symptoms. The most common cause of cauda equina syndrome is compression by a herniated intervertebral disk.
In clinical practice, it may be challenging to distinguish between cauda equina syndrome and conus medullaris syndrome, because the presentation may overlap significantly. Because the conus medullaris is a part of the spinal cord, isolated conus medullaris syndrome typically presents with upper motor neuron findings. Patients may present with a constellation of symptoms indicating a combination of cauda equine and conus medullaris syndromes. Bilateral symptoms might be a helpful factor in distinguishing conus medullaris syndrome. The conus is a relatively small structure, and its compression is likely to give bilateral symptoms. Also, the presence of severe pain in this patient is more suggestive of a cauda equina than a conus medullaris syndrome. (Tarulli, 146–158; Marx, 1419–1427)
Tarulli A. Disorders of the cauda equina. Continuum. February 2015; 21:146–158.