A 48-year-old woman presented to the emergency department with a 3-week history of bilateral lower extremity paresthesias, weakness, and progressive dyspnea. Her symptoms began with numbness in her feet and gradually progressed proximally to involve her knees and hands. Eventually, progressive weakness developed in the same distribution. She had difficulty climbing stairs and going from a seated to a standing position. Her most recent symptoms included exertional dyspnea, now present at rest. She had not experienced diplopia, slurred speech, dysphagia, difficulty holding her head, or back pain.