Clinical Reasoning: A 64-year-old man with progressive paraspinal muscle weakness

A 64-year-old man was referred with a 5-month history of progressive muscle weakness. He first noted a stooped posture and gait difficulties, followed by difficulty climbing and descending stairs and lifting dishes up onto high shelves. The progressive severity of his weakness led him to require a wheelchair by the time of his presentation. He was unable to sit unaided, presumably because of axial weakness. In addition, he had recently started to experience bulbar symptoms, including dysphagia and voice changes, along with shortness of breath on exertion or when lying flat. He denied visual symptoms, ptosis, and facial weakness. There was no diurnal fluctuation of symptoms. He had no sensory symptoms or sphincter disturbance. There was no family history of muscle disease. However, his family history was positive for a child with chronic inflammatory demyelinating polyneuropathy, starting at age 16, with good response to periodic IV immunoglobulin (IVIg), and another child with acute inflammatory demyelinating polyneuropathy, who recovered fully.