Autoantibodies in sporadic Creutzfeldt-Jakob disease.

IMPORTANCE: The diagnosis of autoimmune and neurodegenerative conditions can be unclear. Treatments such as removing the associated tumor, if present, and immunosuppression can halt or often reverse the progression of autoimmune conditions, but there is no curative treatment for neurodegenerative conditions. The presence of autoantibodies can sometimes be misleading. This report illustrates potential difficulties in differentiating autoimmune encephalopathies from sporadic Creutzfeldt-Jakob disease. OBSERVATIONS: In a clinical follow-up of an older man with rapidly evolving encephalopathy at a neuroscience center, unsuccessful treatment with immunosuppression based on the incorrect presumptive diagnosis of Morvan syndrome was followed by the correct histological diagnosis of sporadic Creutzfeldt-Jakob disease. CONCLUSIONS AND RELEVANCE: Autoimmune encephalopathies raise important treatment options and potential for recovery. However, since neuronal antibodies may be positive in prion disease, interpretation can be complex and must be rooted in the clinical picture.