Proprioceptive Stimuli as a New Type of Trigger for Epilepsy in Stiff Person Syndrome.

A healthy 74-year-old woman was diagnosed with Stiff-Person (SP) syndrome (encephalopathy and stiff leg) with amphiphysin autoantibodies and T1N1M0 breast cancer (HER2+, PR-, ER-). She received immunotherapy (2 high-dose steroid cycles and 7 plasmapheresis sessions), followed by right mastectomy, axillary chain lymphadenectomy, and adjuvant chemotherapy (letrozole, trastuzumab, and cyclophosphamide), with poor clinical response (Eastern Cooperative Oncology Group 4). After discharge, she presented to the emergency department with seizures induced by knee flexion of the stiff leg (Video 1). EEG showed epileptic seizures initiating in the left temporal lobe (Figure). Reduced presynaptic GABAergic inhibition could be the underlying mechanism of the core signs of amphiphysin-SP, which might explain the presence of epilepsy in these patients.(1) However, no reflex proprioceptive seizures had been previously reported in SP.