The Nosologic Validity of Paranoia (Simple Delusional Disorder)

The diagnostic status of paranoia (renamed simple delusional disorder SDD) has been debated since the time of Kraepelin. Three main views have emerged that consider paranoia (1) a subtype of schizophrenia, (2) a subtype of affective illness, or (3) a distinct nosologic entity. The literature pertinent to the diagnostic validity of a SDD is examined. Although the methodology of a number of the studies reviewed would not be considered rigorous by today's standards, certain tentative conclusions can nonetheless be reached. The available data do not suggest that SDD is a subtype of affective illness. The evidence reviewed also does not strongly support the hypothesis that SDD is a subtype of schizophrenia. Although some of the data is consistent with the view that SDD is a "mild" form of schizophrenia, the bulk of the evidence suggests that SDD and schizophrenia are distinct syndromes.