Delusions are beliefs that are held by an individual with strong conviction, despite evidence presented to the contrary. A very rare psychological condition, delusional disorder sees patients obsessed with delusions, without any accompanying hallucinations or other symptoms. Individuals diagnosed with delusional disorder are often able to lead somewhat normal lives, although their continuing delusional beliefs can become disruptive.
According to the Diagnostic and Statistical Manual of Disorders (DSM), there are seven different types of delusional disorders. Erotomania is the delusion that another person is in love with the delusional individual. Grandiose type involves the individual having an inflated sense of self, such as being a famous person. Jealous type involves believing one's partner to be unfaithful, often involving invasive actions. Persecutory types believe that they are being unfairly treated and may seek legal redress. Somatic type delusions involve a perceived physical defect or medical condition. There are also mixed and unspecified types of delusional disorder.
There is no known cause for delusional disorder, although there may be imbalances in the brain's neurotransmitters. Similar to schizophrenia, individuals with delusional disorder have less invasive symptoms and are better able to function in society.