The term paranoia is confusing since different psychiatric traditions have used it to describe different constructs. Originally, paranoia (Greek for “beside the mind”) was simply a general term for madness. In the 19th century, Kraepelin and others used paranoia to designate a specific type of psychiatric illness, characterized by a delusional process that results in a clinical syndrome with delusion that would eventually engulf a person’s whole experience and actions. Such systematized and entrenched delusions (i.e., everything gets fitted into the paranoid frame of mind) are notoriously difficult to challenge and change. The person’s personality outside the delusions remained intact, in contrast to schizophrenia with its negative symptoms and formal thought disorder.
Paranoia as used in descriptive psychopathology is not restricted to persecutory delusions but refers to any delusion that results from the postulated delusional process. Understanding the moderators and predisposing factors that lead to the development of (usually) understandable delusions was a major effort of 19th and 20th century psychopathology and continues to be of great interest (e.g., how do social cognitions form; the role of trauma in delusion formation; the cognitive perspective of delusion formation).
Called paranoia in DSM-III, this term for the clinical syndrome was eventually dropped and replaced by Delusional Disorder in DSM-IV. Notably, paranoia is also no longer used to describe symptoms of schizophrenia or to indicate a subtype of schizophrenia. In the older psychiatric literature, the paranoid subtype of schizophrenia was recognized as a type with predominance of paranoia – in the broad sense of delusions (and not limited to persecutory delusions although those are very common). Paranoid Personality Disorder still contains the term paranoid, indicating a style of thinking and interpreting the world through a lens of distrust and suspiciousness. Themes of exploitation, fear of harm and deceit are typical. Paranoid patients look for hidden meaning in utterances, misinterpret innocent mistakes as intentional, and take everything personally; grudges are held tenaciously, particularly if loyalty is questioned and betrayal suspected. As a personality disorder, paranoid indicates a habitual style of thinking and not the presence of delusions.
Kendler KS. The clinical features of paranoia in the 20th century and their representation in diagnostic criteria from DSM-III through DSM-5. Schizophrenia Bulletin. 2017;43(2):332-343.