Clinical reasoning: a 49-year-old woman with progressive motor deficit.

A previously healthy 49-year-old woman presented with progressive motor deficit. The complaints started the year before with weakness of the right arm. Over the subsequent months, she developed weakness in the left arm, followed by both legs, and, finally, difficulty speaking, with nasal voice, and swallowing. It was increasingly difficult to attend to her chores, and, by the time she sought medical attention, she needed help with all daily activities. In the last few weeks, she also complained of diffuse joint and muscle pain. Medical and family history were unremarkable.