Delusional disorder is a mental illness in which patients have delusions for different periods of time. Delusions are bizarre and they cannot be diagnosed easily until someone touches there delusional themes. Delusions are varied and patients are classified according to them.
“Delusional disorder is a mental illness in which the patient presents with delusions, but with no accompanying prominent hallucinations, thought disorder, mood disorder, or significant flattening of effect. Delusions are a specific symptom of psychosis. Delusions can be “bizarre” or “non-bizarre” in content; non-bizarre delusions are fixed false beliefs that involve situations that could potentially occur in real life, such as being followed or poisoned. Apart from their delusions, people with the delusional disorder may continue to socialize and function in a normal manner and their behavior does not necessarily generally seem odd. However, the preoccupation with delusional ideas can be disruptive to their overall lives.
For the diagnosis to be made, auditory and visual hallucinations cannot be prominent, though olfactory or tactile hallucinations related to the content of the delusion may be present. The delusions cannot be due to the effects of a drug, medication, or general medical condition, and delusional disorder cannot be diagnosed in an individual previously properly diagnosed with schizophrenia. A person with delusional disorder may be high functioning in daily life. Recent and comprehensive meta-analysis of scientific studies points to an association between a deterioration in aspects of IQin psychotic patients, in particular, perceptual reasoning.
According to German psychiatrist Emil Kraepelin, patients with delusional disorder remain coherent, sensible and reasonable. The Diagnostic and Statistical Manual of Mental Disorders (DSM) defines six subtypes of the disorder characterized as erotomanic (believes that someone is in love with them), grandiose (believes that they are the greatest, strongest, fastest, richest, or most intelligent person ever), jealous (believes that the love partner is cheating on them), persecutory (delusions that the person or someone to whom the person is close is being malevolently treated in some way), somatic (believes that they have a disease or medical condition), and mixed, i.e., having features of more than one subtype. Delusions also occur as symptoms of many other mental disorders, especially the other psychotic disorders.” https://en.wikipedia.org/wiki/Delusional_disorder