Ophthalmoplegia and Downbeat Nystagmus in Stiff-Person Syndrome

Stiff-person syndrome (SPS) is a poorly understood condition with generalized stiffness and rigidity thought to be centrally mediated. Diagnosis is supported by the presence of glutamic acid decarboxylase antibodies (GADab). Abnormal eye movements are infrequently reported in SPS and were attributed to co-existent myasthenia in early cases. Recent reports suggest GADab as a direct cause. GADab have also been reported with downbeat nystagmus (DBN) with or without ataxia in the absence of SPS.