Delusional disorder is sometimes confused with schizophrenia as both share delusions as a characteristic. What distinguishes delusional disorder is the presence of plausible delusions, as opposed to the more bizarre delusions that may accompany schizophrenia. Delusions are generally thought of as fixed false beliefs. The 'fixed' element refers to the fact that even in the face of evidence to the contrary, the delusion remains. In delusional disorder there is evidence to suggest that with proper treatment delusions may not always be fixed.
People with delusional disorder are usually in their 40s and may not realise they have a problem until it is pointed out to them by a friend or relative. The lack of feedback may be one of the reasons why some people develop, maintain and possibly act on their delusion. Studies of people with the disorder have revealed that they are often socially isolated and many may have a physical problem such as deafness or visual impairment.
The most common delusions are subtyped into the following categories:
Erotomania: more common in females, erotomania refers to the firm belief that someone (often of a higher status) is in love with them. The nature of the love is all-consuming, but pure and romantic rather than sexual in nature.
Grandiosity: some people have a firm belief that they have a great talent or ability that is being ignored or overlooked. This would be typical of a grandiose form of delusion. Grandiosity may also take the form of a particularly significant relationship with someone that others do not share.
Jealousy: as the category suggests, jealousy relates to the firm belief that one's partner or spouse is being unfaithful.
Persecutory: the belief that some plot or conspiracy is being hatched to do the person harm or discredit them.
Somatic: the belief that the person has some infection, has an unpleasant body odor, is disfigured or perhaps infested with lice or other creatures.
Other: there are other forms of delusion that do fit into the main categories. For example, Capgras syndrome refers to the belief that a familiar person has been replaced by an imposter. Fregoli syndrome refers to the belief that a familiar person is disguised as someone else. Cotard syndrome refers to the belief that the person has lost everything, including their internal organs, their strength and their possessions. Cotard syndrome is rare and tends to be thought of as a precursor to a depressive or schizophrenic episode.
Nothing is really know about the cause of the disorder and because the person's life is generally otherwise unaffected many individuals may never even be recognized as having a problem. The exceptions are often those who come to the attention of the law and/or the media resulting from actions they have taken stemming from the delusion. Examples could be stalking or revenge attacks or assault.
Cognitive therapy has been shown to have some beneficial effects. The therapist helps the person to identify dysfunctional thought processes and replace these with more adaptive beliefs. Antipsychotic medication also helps although the available research in this area is limited and varied. Munro & Mok (1995) reviewed 1000 treatments between 1965-1985 and concluded that roughly half had a good prognosis if treated appropriately.
Guryanova, Irene (2006, June, 15). Delusional Disorder. eMedicine, Retrieved 04/24/2008, from http://www.emedicine.com/med/topic3351.htm
Munro, A, Mok H (1995) An overview of treatment in paranoia/delusional disorder. Canadian Journal of Psychiatry, 40(10): 616-22