GAD1 and type 1 diabetes mellitus: Anti-Glutamic Acid Decarboxylase (GAD) encephalitis: Anti-GAD antibodies are not typically associated with malignancy but associated with other non-neoplastic autoimmune conditions such as type 1 diabetes mellitus. Classic temporal lobe lesions on magnetic resonance (MR) imaging with the expected clinical findings of limbic encephalitis plus additional features of stiff person syndrome