A 53-year-old man comes to the emergency department due to severe lower back pain. The patient's back pain started 2 weeks ago without any preceding trauma and has been keeping him awake at night. The pain has acutely worsened over the past 2 days and is not relieved with over-the-counter pain medications. His vital signs are within normal limits. Examination shows low back pain that is worse with back flexion and raising of the legs; it radiates into his left leg. Pinprick in the perianal area does not cause rapid contraction of the anal sphincter. The rest of the neurologic examination is normal. Which of the following nerve roots is most likely to be involved in this patient's condition?

Question

A 53-year-old man comes to the emergency department due to severe lower back pain.  The patient's back pain started 2 weeks ago without any preceding trauma and has been keeping him awake at night.  The pain has acutely worsened over the past 2 days and is not relieved with over-the-counter pain medications.  His vital signs are within normal limits.  Examination shows low back pain that is worse with back flexion and raising of the legs; it radiates into his left leg.  Pinprick in the perianal area does not cause rapid contraction of the anal sphincter.  The rest of the neurologic examination is normal.  Which of the following nerve roots is most likely to be involved in this patient's condition?

Quizplus · Accepted Answer

11ec160b_35a2_413d_9249_9d879a55f084_MD0001_00 This patient's worsening low back pain with a positive straight leg test is consistent with subacute lumbosacral radiculopathy, which most often occurs due to a herniated disk; less common causes include neoplasm, fracture, or epidural hematoma/abscess. Compression of the spinal cord and/or nerve roots can cause a wide range of deficits based on the level(s) involved. This patient's perianal anesthesia with loss of the anocutaneous reflex indicates involvement of the S2-S4 nerve roots. In an adult, the spinal cord terminates in a tapering fashion as the conus medullaris (T12-S4) at the L1-L2 vertebral level. The collection of spinal nerves below this point (eg, L3-S4) exit inferiorly through their respective intervertebral foramina and are referred to as the cauda equina (ie, horse's tail). Lesions at the L1-L5 vertebral levels can affect the conus medullaris and/or T12-S4 nerve roots, resulting in a characteristic constellation of symptoms: This pattern of neurologic deficits can occur with either conus medullaris syndrome (lesions around L1-L2 vertebrae) or cauda equina syndrome (lesions below L2 vertebra). Conus medullaris syndrome typically causes bilateral, symmetric lower extremity weakness with upper motor signs (eg, spasticity, hyperreflexia), while cauda equina syndrome tends to cause flaccid, asymmetrical lower extremity weakness. Due to the potential for further neurologic deterioration, affected patients require urgent evaluation including MRI of the spine. (Choice A) Compression of the T12 nerve roots would result in lower abdominal or groin pain. (Choices B and C) The L2-L4 spinal nerve roots contribute to the femoral nerve and mediate the quadriceps (ie, patellar) reflex. Lesions affecting these levels would cause loss of this reflex as well as anterior thigh sensory loss or paresthesia. (Choice D) Lesions affecting the L5 nerve root would cause sensory loss or paresthesia over the lateral thigh and anterior calf. (Choice E) The S1 nerve root supplies the Achilles reflex along with sensation to the posterior leg and posterolateral calf. Although the Achilles reflex can be affected in patients with lumbosacral radiculopathy, this patient does not have evidence of S1 nerve root involvement on examination. Educational objective: Compressive lesions (eg, disk herniation, tumors) affecting the L1-L5 vertebral levels can impinge upon the conus medullaris and/or T12-S4 nerve roots, causing radicular low back pain, changes in bowel/bladder function, saddle/perianal anesthesia (eg, loss of anocutaneous reflex), and lower extremity weakness. Perianal sensation is carried by the S2-S4 nerve roots. __________ References: Cauda equina syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/18664636) Definitions of traumatic conus medullaris and cauda equina syndrome: a systematic literature review (http://www.ncbi.nlm.nih.gov/pubmed/28534496)

A 53-Year-Old Man Comes to the Emergency Department Due to Severe