Schizophrenia (from the Greek schizo - "split", phren - "mind, soul") is a progressive (progredient) endogenous mental disease, characterised by loss of integrity of mental functions, impaired thinking, impoverishment of their emotional sphere (immobility of emotions, according to E. Bleuler) and growing weakening of mental activity (weakening of the energy of their mental life, according to S. Korsakoff, drop of the energetic potential, according to K. Conrad). In addition to these main symptoms, without the presence of which the diagnosis is doubtful, supplementary symptoms also emerge: obsessions, senestopathies, hysterical, hypochondriac symptoms; delusional, hallucinatory, pseudohallucinatory disorders, depressive, manic, catatonic, and oneiric-catatonic manifestations. Supplementary symptoms, as E. Bleuler has called them, can or cannot exist while the main symptoms are present in all cases. Memory and previously acquired knowledge are kept, so the intellect proper does not suffer from schizophrenia.
In the ICD-10, schizophrenia is coded under heading F2. As an independent nosological form, this mental disease was distinguished by the famous German psychiatrist Emil Kraepelin in 1896 and was called "early imbecility" (dementia praecox). Having conducted long-term observations of various patients who experienced acute psychosis with the clinical picture of delusional, hallucinatory-delusional disorders, amentia, confusion, acute depressive delusional or manic-delusional disorders and catatonia, he noted that the final stages of the disease after 10, 15 or 20 years were characterised by their common property. This is manifested as an impoverishment of the entire mental life of patients, loss of their interest in life, and growing general stupidity (Verblödung, which in German means "growing stupidity"). This fatal imbecility final in quite young people was considered by E. Kraepelin to be the main property of the disease; from this, it follows the term "early imbecility". The term "schizophrenia" was offered by the prominent Swiss psychiatrist E. Bleuler in 1911. He considered that schizophrenia was a group of diseases of endogenous origin united by a common psychological symptom that is the splitting of the holistic psyche, loss of integrity of thinking processes, emotions, and affects with the decline in activity.