Summary

We present a rare case of N-methyl-D-aspartate receptor (NMDAR) encephalitis in a 41-year-old Caucasian woman, who initially presented with prominent neuropsychiatric symptoms on the background of pre-existing multiple sclerosis. Here, the authors navigate the muddy water between neurology and psychiatry, describing the caveats of antibody testing with a misdiagnosed case of acute and transient psychotic episode. NMDAR encephalitis in MS is a rare condition, which can be easily confused with a new onset psychotic episode. This case report can be helpful in recognition and diagnosis of this rare condition. Making the right diagnosis is important since it can prevent an unnecessary radical treatment and long-term neuropsychiatric complications.