Paraphrenia is a group of psychotic illnesses distinct from paranoia and from schizophrenia. In patients suffering from this type of psychosis, personality decay is minimal, and emotional rapport is well retained. The onset occurs around age 40.
Furthermore, paraphrenia is characterized by the preoccupation with one or more semisystematized delusions. These delusions are not encapsulated from the rest of the personality as in delusional disorder. The affect is notably well-preserved and appropriate, as is the ability to maintain rapport with others. There is no intellectual deterioration, no flat nor grossly inappropriate affect. Disturbance of behavior is understandable in relation to the content of the delusions. The illness is associated with distress and agitation. Irrational behaviour may appear as delusions become more vivid and judgment lessens. Patients may accuse others of persecution and complain to the authorities.
The predisposing factors in the onset of the disease are associated with severe stressors such as social isolation, migrant status and deafness.
Paraphrenia was coined by Karl Ludwig Kahlbaum in 1863 not to name some specific disorder, but to draw attention that certain psychiatric disorders tend to develop at a certain age. Kahlbaum used for instance to distinguish between paraphrenia hebetica (the insanity of the adolescence) from paraphrenia senilis (the insanity of the elders).
In 1913 Emil Kraepelin revived the term to denote a comparatively small group of cases which he thought were sufficiently distinct from schizophrenia. Kraepelin distinguished paraphrenia from schizophrenia mainly by its course; according to him, patients with paraphrenia showed a "far sligheter development of the disorders of emotion and volition" compared to schizophrenia. Although Kraepelin did not give an explanation for his choice of terminology, clinical psychologist P. J. McKenna speculates that Kraepelin might have wished to emphasize a relation to paranoid schizophrenia on one hand, and with paranoia on the other. Kraepelin's paraphrenia concept however was controversial from the outset. One of his contemporaries, Wilhelm Mayer followed up a group of Krapelin's original paraphrenic patients and concluded that with, the passage of time, patients with paraphernia tend to merge into the pool of chronic schizophrenic patients.