A 62-year-old man comes to the emergency department due to acute-onset constipation. His last bowel movement was 4 days ago; before that time, his stools were always regular. Review of systems is positive for dry cough, increasing low back pain, a 9-kg (20-lb) weight loss in the past month, and increasing difficulty with urination. He has smoked 2 packs of cigarettes daily for 30 years. Vital signs are within normal limits. Point tenderness is elicited with palpation over the lower spine. Bilateral lower extremity weakness is present, and sensation is impaired in the perineal region. Chest x-ray reveals a right lung mass. Dysfunction of which of the following nerves best explains this patient's constipation?

Question

A 62-year-old man comes to the emergency department due to acute-onset constipation.  His last bowel movement was 4 days ago; before that time, his stools were always regular.  Review of systems is positive for dry cough, increasing low back pain, a 9-kg (20-lb) weight loss in the past month, and increasing difficulty with urination.  He has smoked 2 packs of cigarettes daily for 30 years.  Vital signs are within normal limits.  Point tenderness is elicited with palpation over the lower spine.  Bilateral lower extremity weakness is present, and sensation is impaired in the perineal region.  Chest x-ray reveals a right lung mass.  Dysfunction of which of the following nerves best explains this patient's constipation?

Quizplus · Accepted Answer

This patient with a lung mass has progressive low back pain, bilateral lower extremity weakness, bowel/bladder dysfunction, and impaired perineal sensation; this presentation is highly concerning for cauda equina syndrome. The cauda equina is formed from lumbosacral nerve roots which can be compressed by epidural metastasis (most commonly from lung cancer), trauma, or disc herniation. The symptoms of cauda equina syndrome result from disruption of nerve roots to the sciatic nerve (eg, lower extremity weakness, radicular low back pain), pudendal nerve (eg, saddle anesthesia), and/or pelvic splanchnic nerves. The pelvic splanchnic nerves (S2-S4) provide parasympathetic innervation to the hindgut, bladder, and urinary sphincters that promotes peristalsis, bladder emptying, and pelvic floor relaxation during defecation. Constipation and difficulty urinating are prominent symptoms in cauda equina syndrome due to loss of parasympathetic input to the bowel and bladder. (Choices A and C) The greater splanchnic nerve (T5-T10) and lesser splanchnic nerve (T9-T12) provide sympathetic innervation to the foregut and midgut, respectively. In contrast to the parasympathetic nervous system, the sympathetic nervous system inhibits the gastrointestinal tract by slowing peristalsis. Disruption of these nerves can lead to increased gut motility, not constipation. (Choice B) The ilioinguinal nerve (L1) provides sensation to the superior medial thigh and part of the genitals, as well as motor innervation to the transverse abdominus and oblique abdominal musculature. Although it can be affected in cauda equina syndrome, it does not provide sympathetic or parasympathetic innervation to the gastrointestinal system. (Choice E) The vagus nerve (CN X) originates in the medulla and provides parasympathetic innervation to the proximal gastrointestinal tract, ending at the level of the splenic flexure. Impairment of the vagus nerve is more likely to cause delayed gastric emptying and would not be caused by a lumbosacral spinal cord lesion. Educational objective: The pelvic splanchnic nerves (S2-S4) provide parasympathetic innervation to the bowel and bladder, and their impairment in cauda equina syndrome can cause constipation and difficulty urinating. Other signs of cauda equina syndrome include radicular low back pain and leg weakness (sciatic nerve) as well as saddle anesthesia (pudendal, ilioinguinal nerves). __________ References: Constipation in neurological diseases. (http://www.ncbi.nlm.nih.gov/pubmed/12486259)

A 62-Year-Old Man Comes to the Emergency Department Due to Acute-Onset