Q. What are the differences between paranoid personality disorder, paranoia or delusional disorder and paranoid schizophrenia. Specifically, what is the difference in the causes of each? Do they all involve a chemical imbalance or is that just in schizophrenia?

A. Not to be flippant, but if I knew the answers to these questions, I might be up for a Nobel Prize! Unfortunately, we really do not know the ultimate causes of any of the conditions you are asking about. We do have quite a bit of evidence that schizophrenia is powerfully driven by biogenetic factors, and that abnormalities in the brain chemical dopamine are strongly implicated.

As for delusional disorder (paranoia) and paranoid personality disorder, we have a very rudimentary understanding of their causes. Much less research has focused on these conditions, since we do not see them nearly as frequently as we see schizophrenia. But maybe I can at least explain the differences between these diagnoses. In delusional disorder (DD)--which can occur in a variety of types-the individual has a specific, circumscribed loss of reality testing. That is, the person with DD has a particular delusional belief-such as "The FBI is out to get me", or "Clint Eastwood is in love with me"--without any other major disturbance in thinking, mood, behavior, intellectual function, or beliefs.

The individual with DD typically does not experience auditory or other hallucinations, and usually has relatively normal thought processes. DD generally begins later in life than does schizophrenia. A person with DD, for example, might behave relatively normally in an office setting, so long as his or her particular delusional belief did not come up. In contrast, the individual with schizophrenia shows profound impairments in social, vocational, and usually cognitive function.It is a pervasive disorder that affects nearly all aspects of life.

The individual with schizophrenia typically shows abnormalities in speech, thought process, emotional expressiveness, and behavior--as well as experiencing delusions and hallucinations. Some studies have shown a higher than expected prevalence of DD among the relatives of individuals with schizophrenia, while other studies have found no familial relationship between DD and schizophrenia.

Paranoid personality disorder (PDD) differs from both these disorders in important ways. In PPD, there is no frank delusion present, nor does the individual experience hallucinations (except, perhaps, transiently, during periods of extreme stress). PPD individuals tend to fall under the suspicious loner type. Some secretly entertain grandiose fantasies, such as being the world's greatest writer or inventor. These individuals are often argumentative, litigious, mistrustful, and negativistic about most things in life--for example, if you brought a PPD individual a birthday cake, he would probably wonder what your real motive was. (In contrast, the individual with paranoid schizophrenia, or delusional disorder (persecutory type), might instantly conclude you were trying to poison him).

In some cases, PPD seems to be a precursor to either Delusional Disorder or schizophrenia, and some studies show a higher prevalence of PPD in relatives of individuals with schizophrenia or DD. This might indicate some biochemical similarities among these conditions, but, as I indicated above, very little is known about the underlying biochemical problems in DD or PPD. For much more information about the biogenetic aspects of schizophrenia, you might try contacting the National Alliance for Research on Schizophrenia and Depresssion (516-829-0091).

March 2001

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