Progressive encephalomyelitis with rigidity and myoclonus in an 81-year-old patient.

We present the case of an 81-year-old female with severe rigidity, stiffness and superimposed muscle spasms that represents the oldest reported patient with progressive encephalomyelitis with rigidity and myoclonus. Two associated autoimmune disorders (diabetes mellitus and Hashimoto's thyoiditis) were recently diagnosed. A paraneoplastic origin was excluded. The spectrum of differential diagnoses including classic Stiff-Person syndrome and paraneoplastic Stiff-Person syndrome is discussed.