Review Question - QID 109003

A 69-year-old man presents to his primary care physician with hip and back pain. He states this weekend he had a barbecue. When he was lifting a heavy object, he suddenly felt pain in his lower back. He describes the pain as in his buttocks but states that at times it travels down his leg. He states that it feels electrical and burning in nature. The patient has a medical history of obesity, diabetes, depression, anxiety, diverticulosis, constipation, and a surgical repair of his anterior cruciate ligament. His current medications include metformin, insulin, lisinopril, fluoxetine, and sodium docusate. His temperature is 98.6°F (37°C), blood pressure is 131/82 mmHg, pulse is 82/min, and respirations are 14/min. On physical exam, he is found to have an intact motor and sensory function in his lower extremities bilaterally. No clonus or Babinski sign is appreciated. An exam of the cranial nerves is intact bilaterally. Which of the following is most likely to help confirm the diagnosis?