This disorder is characterized by the presence of non-bizarre delusions which have persisted for at least one month. Non-bizarre delusions typically are beliefs of something occurring in a person's life which is not out of the realm of possibility. For example, the person may believe their significant other is cheating on them, that someone close to them is about to die, a friend is really a government agent, etc. All of these situations could be true or possible, but the person suffering from this disorder knows them not to be (e.g., through fact-checking, third-person confirmation, etc.).
People who have this disorder generally don't experience a marked impairment in their daily functioning in a social, occupational or other important setting. Outward behavior is not noticeably bizarre or objectively characterized as out-of-the-ordinary.
The delusions can not be better accounted for by another disorder, such as schizophrenia, which is also characterized by delusions (which are bizarre). The delusions also cannot be better accounted for by a mood disorder, if the mood disturbances have been relatively brief.
The delusion may manifest itself as any of the following types:
Persecutory type in which the individual believes he or she is being threatened or mistreated my others.
Grandiose type, in which victims of the disorder believe that they are extraordinarily important people or are possessed of extraordinary power, knowledge or ability.
Jealous type, in which the delusion centers on the suspected unfaithfulness of a spouse or sexual partner. This delusion is more common than others.
Eroticmatic type, in which individuals convince themselves some person of eminence, often a movie star or well-known political figure (often whom they have never met but to whom they have written frequently) is in love with them.
Somatic type, in which the false belief focuses on a delusional physical abnormality or disorder.
One extremely rare instance of this disease is called folie à deux. It results from a close relationship with someone else who already has a delusional disorder, often under a closed environment. Both persons then share the delusion, such as the situation in the movie "Nell," where the main character is raised away from society with only her sister to associate with.
It is important to note the distinguishment between this disorder and paranoid schizophrenia, which is that in this disorder, the symptoms of hallucination, incoherence, and loosened association are not present.
This disorder occurs in middle-aged to older persons, however it is free from further deterioration or any type of remission. Typical is the diseased's unwillingess to participate in treatment or associate casually.
It is generally believe that this the delusional disorder stems not from genetic or physical means, but rather from pathological early life experiences.