Psychosis is often defined as "impaired reality testing" - whatever "reality" means.
A psychotic person experiences the world differently from others around them, making it difficult to function.
Psychosis includes experiences such as hallucinations, unusual beliefs and disorganized thoughts and behavior.
Clinical features
Psychosis typically strikes early in adulthood and often leads to significant impairment. The hallmark features of psychotic disorders are delusions and hallucinations, but disorganization of thought, bizarre behavior, and a withdrawal from social contact are equally impairing, if not more so.
The various forms of psychotic disorders differ in their clinical presentation and with regard to course and outcome.
Psychotic patients need to be carefully examined for a variety of medical or neurological conditions as well as the recent use of various drugs, since these conditions deserve proper intervention, possibly leading to complete resolution of psychosis.
Schizophrenia is the most severe psychotic disorder and affects close to 1% of us.
An additional 2% are being diagnosed with other psychotic disorders, which are less severe or are of shorter duration.
Mechanism
The mechanism of psychosis remains obscure.
Schizophrenia is one of the most heritable psychiatric disorders, but unraveling the molecular mechanism has been slow. Recently, several risk genes have been identified, but they do not determine the illness. In addition, several environmental risk factors (including traumatic life events and early consumption of marijuana) play a small, but significant, role.
Much research has focused on structural brain changes in schizophrenia. Slight decreases of brain volume are often seen, but they cannot be used to make the diagnosis. The complex and often changing abnormalities of behavior have been associated with abnormal brain function, but they are not a consistent finding and do not define psychosis.
Treatment
We have seen great progress in the treatment of psychotic disorders. Before the 1950s, we had mostly ineffective treatments.
Antipsychotic medications were discovered in the 1950s. They block dopamine receptors in the brain and treat delusions, hallucinations and disorganization.
In the last 20 years, we have seen the development of a new generation of antipsychotic medication and successful psychotherapeutic treatment.
Outcome
The course and outcome of psychotic disorders can vary tremendously. Recovery from symptoms should always be the goal.
Some patients will do well in the long run, even without treatment. Many patients will continue to experience symptoms and benefit from treatment. Some patients require close clinical attention and need financial assistance and help with housing.
Some interesting postings on the topic of psychosis:
Answers by attendees of the ISPS conference in Liverpool, UK, in 2017
A thoughtful TEDx talk by psychiatrist-neuroscientist Paul Fletcher