Delusional disorder is characterized by firmly held false beliefs (delusions) that persist for at least 1 month, without other symptoms of psychosis.

Delusions are distinguished from mistaken beliefs in that delusional beliefs remain unchanged in the face of clear, reasonable evidence to the contrary; this distinction is sometimes difficult to make when the beliefs are more plausible (eg, that a spouse is unfaithful).

Delusional disorder is distinguished from schizophrenia by the presence of delusions without any other symptoms of psychosis (eg, hallucinations, disorganized speech or behaviour, negative symptoms). The delusions may be

• Nonbizarre: They involve situations that could occur, such as being followed, poisoned, infected, loved at a distance, or deceived by one’s spouse or lover.
• Bizarre: They involve implausible situations such as believing that someone removed their internal organs without leaving a scar.

In contrast to schizophrenia, delusional disorder is relatively uncommon. Onset is generally involutional, occurring in middle or late adult life. Psychosocial functioning is not as impaired as it is in schizophrenia, and impairments usually arise directly from the delusional belief.

When delusional disorder occurs in older patients, it is sometimes called paraphrenia. It may coexist with mild dementia. The physician must be careful to distinguish delusions from elder abuse being reported by a mildly demented older patient.

• Symptoms and Sign of Delusional Disorder

Delusional disorder may arise from a preexisting paranoid personality disorder. In such people, a pervasive distrust and suspiciousness of others and their motives begin in early adulthood and extend throughout life.

Early symptoms may include the feeling of being exploited, preoccupation with the loyalty or trustworthiness of friends, a tendency to read threatening meanings into benign remarks or events, persistent bearing of grudges, and a readiness to respond to perceived slights.

Several subtypes of delusional disorder are recognized:

• Erotomaniac: Patients believe that another person is in love with them. Efforts to contact the object of the delusion through telephone calls, letters, surveillance, or stalking are common. People with this subtype may have conflicts with the law related to this behaviour.
• Grandiose: Patients believe they have a great talent or have made an important discovery.
• Jealous: Patients believe that their spouse or lover is unfaithful. This belief is based on incorrect inferences supported by dubious evidence. They may resort to physical assault.
• Persecutory: Patients believe that they are being plotted against, spied on, maligned, or harassed. They may repeatedly attempt to obtain justice through appeals to courts and other government agencies and may resort to violence in retaliation for the imagined persecution.
• Somatic: The delusion relates to a bodily function, eg, patients believe they have a physical deformity, odor, or parasite.

Patients' behaviour is not obviously bizarre or odd, and apart from the possible consequences of their delusions (eg, social isolation or stigmatization, marital or work difficulties), patients' functioning is not markedly impaired.

• Diagnosis of Delusional Disorder
• Clinical evaluation

Diagnosis depends largely on making a clinical assessment, obtaining a thorough history, and ruling out other specific conditions associated with delusions (eg, substance use, Alzheimer disease, epilepsy, obsessive-compulsive disorder, delirium, other schizophrenia spectrum disorders).

Assessment of potential dangerousness, especially the extent to which patients are willing to act on their delusion, is very important.

• The prognosis for Delusional Disorder

A delusional disorder does not usually lead to severe impairment or change in personality, but delusional concerns may gradually progress. Most patients can remain employed as long as their work does not involve things related to their delusions.

• Treatment of Delusional Disorder
• Establishment of an effective physician-patient relationship
• Management of complications
• Sometimes antipsychotics

Treatment aims to establish an effective physician-patient relationship and manage complications. A substantial lack of insight is a challenge to treatment.

If patients are assessed to be dangerous, hospitalization may be required.

Insufficient data are available to support the use of any particular drug, although antipsychotics sometimes suppress symptoms.

A long-term treatment goal of shifting the patient’s major area of concern away from the delusional locus to a more constructive and gratifying area is difficult but reasonable.