Supplemental data at Neurology.org

Tonic eye deviation in stiff-person syndrome PEARLS 1. Stiff-person syndrome (SPS) is an autoimmune disease characterized by muscle rigidity, episodic muscle spasms, as well as continuous cocontrac-tion of agonist and antagonist muscles. 2. Although a criterion for diagnosis of SPS, anti– glutamic acid decarboxylase (anti-GAD) antibod-ies can be negative in up to 40 % of patients. In absence of antibodies, characteristic EMG find-ings of continuous motor unit activity and decrease in this activity with diazepam are helpful in diagnosis. OY-STER