Differentiating Psychotic Disorders

Psychosis means out of touch with reality. Reality is defined by the consensus of the majority.  Insaniety has been differentiated from genius in that insane people are said to lack the 'marketting agent' associated with 'genius'.  The actual psychosis may range from paranoid and isolative to grandiose and innappropriately inclusive.
Delirium is distinguished from psychosis in that with delirium the person's cognitive function is impaired, clearly so, and the persons' comprehension and orientation are severely disturbed. A person with delirium appears to shift in and out of awareness. Deliriums are acute processes of hours or days whereas dementias which mostly impair memory, orientation and awareness tend to persist.. These are there fore distinct from psychosis where the persons sense of time and place and awareness and memory may well be in tact.
The 'monosymptomatic delusional' person is a particularly interesting psychosis. This person appears to all and sundry perfectly normal.  They commonly hold successful positions in the community, often have senior positions and families.  Their psychosis indeed only appears if one triggers it with a statement or question.  An example was an individual who believed Jews were controlling the world.  He worked as a beaurocrat and was perfectly normal unless you mentioned jews. At which point he'd go off into a paranoid diatribe with increasingly bizarre ideation.  Change the subject to the weather and he's normal again.
Psychosis is defined first by 'time'.  Brief Psychotic Reaction refers to a limitted psychotic experience lasting less than 6 months, often only hours or days.
Psychosis are associated with delusions. Eg of delusions are paranoid - feeling people are following one or out to get one without any concrete evidence to support this. (Faced with the Nazi Freud said "sometimes the paranoids are right")
Another psychosis is 'pathological jealousy' in which the person believes a partner is cheating on them.  It's most commonly associated with alcoholism.
Ideas of reference refer to the idea of thinking people are talking about you when they aren't.  Thought insertion is having the sense that people are putting their thoughts or alien thoughts into your head.  Thought broadcasting is the belief that your own thoughts can be heard by others.
Hallucinations are common with psychosis. The most common are auditory hallucinations. Auditory hallucinations may be a voice heard outside the head or two voices or more heard outside. Commonly the voices refer to the person.  Visual hallucinations are more commonly associated with drug abuse, brain injury, or delirium.
In contrast to Brief Psychotic Episodes,  Schizophrenia is a psychotic disorder which may be stabilized by drugs but without treatment may become a permanent psychotic state.  One example is a person who believes the CIA are watching them from pebbles on the street.
Schizophrenia presents in a variety of forms with the best prognosis and most common being 'paranoid'. Hebephrenic Schizophrenia is the bizarre presentation with alot of unusual disconnected thought content.  Undifferentiated and chronic is the most common seen in institutions.  It's a mix of presentions with a lower level and often more repeititive quality.  It is thought that the more acute paranoid without treatment 'burns' out to the 'chronic undifferentiated schizophrenia. The focus of treatment and success of medication treatment is that patients with schizophrenia are mostly treated  in the community where once they lived their lives in institutions.
Schizaffective disorder is a psychotic disorder which is differentiated from schizophrenia by it's  more 'emotional' component. Like schizophrenia it is a life long condiition but has a better prognosis.
Bipolar I disorder, the historic Manic Depression of Kraeplin (not the ubiquitous Bipolar II of the non Kraeplin set) is associated commonly with psychosis. In Mania the psychosis is grandiose with superhuman qualities.  Patients who have had cocaine addiction or amphetamine addiction and bipolar I have described their Mania as being like being on Cocaine or Amphetamine without the drugs.  Cocaine and Amphetamine were studied as drugs that mimicked psychosis.
Bipolar I depressive psychosis or Major Depression with Psychosis is associated with completely negative themes to their experience.  The auditory hallucinations heard by these individuals would be condemning and talking negatively about the patient.  In contrast a purely schizophrenic patient described their auditory hallucinations without emotions 'like listening to the radio'.  Indeed the latter complained of the medication taking away their 'company' and making them 'more lonely'.  Bipolar psychotic depressions have greater 'narcissistic' qualities than a melancholic or unipolar depression with psychosis.  The 'flavour' of uniqueness is noted commonly in both the manic and depressive phases of the Manic Depressive Disorder.
In Schizoaffective disorder and Bipolar Disorder and Depression with psychosis there is still this quality of altered sense of interpersonal humanity which can be absent in the purer Schizophrenic forms where there's a detachment and an alien quality once described as 'pane of glass' though this never stood the test 'diagnostically'.  Psychiatrists still talk of the 'flavour' in lieu of better words.
Drug abuse can mimick psychosis as well as cause psychosis and chronic drug abuse can cause a mild psychotic tendency to become a full blown chronic illness resistant to treatment.
All of the psychosis can be treated medically.  Psychosis that don't respond to standard approaches are now being treated in special 'treatment resistant' services for chronic psychosis. Further there are early intervention units where the thinking is that early treatment may result essentially in 'cure'.  The longer a person is in a psychotic state the greater likelihood that the prognosis can be worse.
There has been abuse of the diagnosis of psychosis.  Psychiatrists Against the Political Abuse of Psychiatry was just one organization that developped to address the tendency of state and individuals to take unfair advantage of individuals with mental illness.  The Canadian Civil Liberties and Canadian Mental Health Association can cite incidences of abuse.  Many grass roots 'ex patient' movements have developed attesting to the potential for abuse.
That said, psychosis is a mental illness that causes individuals great distress. The majority of patients do appreciate and respond to the medications and therapies that relieve them of suffering. The modern psychiatric treatments have served to restore the life and freedom to many who might not have lived beyond the development of their psychosis.  Psychosis is associated with a higher incidence of suicide and risk taking behaviour.
The reason for the need to differentiate the various psychosis is because different psychosis require different treatments.  Further the prognosis is obviously different for the different psychotic illness.  Further the potential for abuse is probably greatest for those 'labelled' with chronic psychosis.  The stigma against psychiatry and psychiatric patients falls most on the patients with psychosis.
Psychotic patients deserve great care and concern including physical examination, neurological examination and complete psychiatric work up including especially drug abuse including marijuania.