In Europe, in the late 19th century and the first half of the 20th century, new nosologic categories were formulated that could not be framed within Manic-Depressive Psycosis or Kraeplins' Demencia Praecox: Bouffée delirante by the French, Cycloid Psychosis by the German, Reactive and Schizophreniform Psychosis by the Scandinavians. These are concepts that are currently classified in the ICD-10 under Acute and Transitory Psychotic Disorders.

Cycloid Psychosis are characterized by an abrupt onset and polimorfic symptomatology namely delusions, hallucinations in every sensory modality, confusion, akinesia or hyperkinesia, feelings of ecstasy, which can vary with time. They have a recurring course, rapid remission followed by the reinstatement of the premorbid personality.

We present a case study of a female, 26 year old patient. The first psychotic episode occurred 2 years ago and was followed by complete recovery. Recently, there was a recrudescence of the symptomatology. She presented with a polimorfic symptoms, alternating between mutism and psychomotor agitation, disorientation, incoherent speech and almost total insomnia. There was an absence of response to antipsychotic medication. Therefore, the patient was submitted to electroconvulsive therapy with an overall improvement of symptoms, maintaining some puerility. The aim of this case study was to draw attention to the diagnosis of Cycloid Psychosis, and it confirms the efficacy of electroconvulsive therapy in its treatment.