Table 2.

Differential diagnosis of primary and secondary psychosis

Primary psychosis	Organic (secondary psychosis)
Brief psychotic disorder: Brief Psychotic Disorder is a thought disorder in which a person will experience short term, gross deficits in reality testing, manifested with at least one of the following symptoms [98]:  Delusions—strange beliefs and ideas resistant to rational/logical dispute or contradiction from others;  Hallucinations—auditory, or visual;  Disorganised Speech—incoherence, or irrational content;  Disorganised or Catatonic behavior—repetitive, senseless movements, or adopting a pose which may be maintained for hours. The individual may be resistant to efforts to move into a different posture, or will assume a new posture they are placed in.  To fulfil the diagnostic criteria for Brief Psychotic Disorder, the symptoms must persist for at least one day, but resolve in less than one month. The psychotic episode cannot be attributed to substance use (ethanol withdrawal, cocaine abuse) or a medical condition (fever and delirium) and the person does not fit the diagnostic criteria for Major Depressive disorder with psychotic features, Bipolar disorder with psychotic features, or Schizophrenia [98]	Delirium: Defined if criteria A–E are fulfilled [98]:  A. Disturbance in attention (i.e., reduced ability to direct, focus, sustain, and shift attention) and awareness (reduced orientation to the environment). B. The disturbance develops over a short period of time (usually hours to a few days) represents a change from baseline attention and awareness, and tends to fluctuate in severity during the course of the day. C. An additional disturbance in cognition (e.g. memory deficit, disorientation, language, visuospatial ability, or perception). D. The disturbances in criteria A and C are not explained by another pre-existing, established, or evolving neurocognitive disorder, and do not occur in the context of a severely reduced level of arousal, such as coma. E. There is evidence from the history, physical examination, or laboratory findings that the disturbance is a direct physiologic consequence of another medical condition, substance intoxication or withdrawal (i.e. because of a drug of abuse medication), or exposure to a toxin, or is because of multiple aetiologies
Acute and transient psychotic disorders (ICD-10: F23 [99]) are with an acute onset and a duration of psychotic symptoms not exceeding 1–3 months. The syndrome develops fully within 2 weeks. It is characterised with psychotic and polymorphic symptoms	Acute encephalopathy [100]: Refers to a rapidly developing (over less than 4 weeks, but usually within hours to a few days) pathobiological process in the brain. It can lead to a clinical presentation of subsyndromal delirium, delirium, or in case of a severely decreased level of consciousness, coma; all representing a change from baseline cognitive status.
Short-lived psychosis triggered by stress: Patients may spontaneously recover normal functioning within 2 weeks. In some instances, individuals may remain in a state of full-blown psychosis for many years, or have attenuated psychotic symptoms (i.e. low intensity hallucinations) present at most times	Poststroke psychosis: Slightly more frequent among males. Neurological presentation is typical for stroke, with lesions present typically in right hemisphere, especially frontal, temporal and parietal regions, and the right caudate nucleus. The most common psychosis appears to be a delusional disorder, followed by schizophrenia-like psychosis and mood disorder with psychotic features. In general, poststroke psychosis is associated with poor functional outcomes and high mortality
Reactive psychosis	Psychosis due to a general medical condition or medication: Symptoms can occur with other medical conditions such as cerebrovascular accident or traumatic brain injury, Wilson’s disease, porphyria, or syphilis infection (also in HIV patients), as well as medications (e.g. steroids) and certain dietary supplements
Psychogenic psychosis: Evidence of incompatibility between the symptom and recognised neurological or medical conditions	Autoimmune psychosis [101]: Subacute onset (rapid progression of less than 3 months) of working memory deficits (short-term memory loss), altered mental status (to include lethargy, personality change, or cognitive deficits), or psychiatric symptoms. Also at least one of the following: new focal CNS findings; seizures not explained by a previously known seizure disorder; cerebrospinal fluid (CSF) pleocytosis (white blood cell count of > 5 cells/mm; MRI features suggestive of encephalitis. Reasonable exclusion of alternative causes