Mrs. O. is a 57 years old secretary. Her past medical history is unremarkable relative to psychiatric disorders or other diseases. She came to the ER because of sudden and severe depressive symptoms, including thoughts of death. Moreover, at times she had brief episodes of confusion during which she displayed depersonalization and short periods of spatial and temporal disorientation.

She was hospitalized in the psychiatric ward and underwent routine blood tests, neurological exams and a MR brain scan, without showing any significant abnormalities. Notably, she presented a maculopapular rash compatible with herpes zoster. Thirteen days later, she was feeling much better and was sent home, with an indication of a psychiatric follow-up. A week later Mrs. O. returned to the ER, since she presented a mixed episode, again with psychotic symptoms. During this second period of hospitalization, Mrs. O. presented persistent mild fever, and more apparent brief moments of spatio-temporal disorientation were noted, accompanied by psychomotor slowness. The impression of an underlying process was further confirmed and a neurological consultation was asked for again. Suspecting viral encephalitis, the patient was admitted to the neurological department and started on acyclovir, demonstrating an initial improvement of the psychiatric symptoms. The follow-up MR brain scan was normal. A suspicion of acute inflammatory demyelinating polyradiculoneuropathy (AIDP) was formulated. Thirty days later Mrs. O.’s deficits in strength were improving steadily and she was transferred to the rehabilitation ward. The psychiatric symptoms had completely receded.