Delusional disorder describes a psychiatric condition where the patient suffers from delusions, but does not suffer from hallucinations, thought disorders, mood disorders or a flat affect. The delusions can be either "bizzare" (could not occur in real life) or "non-bizzare" (could occur in real life).
Most patients with delusional disorder can function normally, but an increasing obsession over their delusions can often result in a disruption of their life.
It is largely a diagnosis of exclusion as all other possible conditions that could cause delusions have to be ruled out, including drugs and organic illnesses that cause delusions. This usually requires a full medical history, including interviews with the patient's friends, and an environmental scan.
The disorder generally presents with one or more of five sub-types - erotomaniac (believing someone is in love with them), grandiose, jealous, persecutory, and somatic (believes they are suffering from a medical disorder).
Treatment can be difficult as patients usually have no sense that their delusions are out of place. Drugs generally have no effect. In most cases, psychotherapy is the preferred course of action with the psychiatrist slowly questioning the patient's delusional beliefs to draw out their own rationality about them. Patients are also given supportive care and coping mechanisms.