Differentials
Schizophrenia
SIGNS / SYMPTOMS
Mood symptoms are either of shorter duration relative to the total duration of the episode of illness, limited to the prodromal phase or residual phases, or fail to satisfy the criteria for a mood episode.[1]
INVESTIGATIONS
No differentiating tests.
Substance-induced psychotic disorder
SIGNS / SYMPTOMS
Delusions are not crystallized, and the patient may have auditory hallucinations and a high level of suspiciousness.
Substance-related disorders are great imitators of psychopathology. In order to prescribe appropriate treatment, accurate diagnosis is necessary. Any substance use evaluation needs to include historical assessment of duration and frequency of use, dose, and time since last use.[37]
INVESTIGATIONS
Urine drug screen, although this is not diagnostic.
Dementia with psychosis
SIGNS / SYMPTOMS
Delusions may be similar to those in schizoaffective disorder, but usually there has been no history of psychosis before the onset of dementia. The age of the patient should be taken into account, and a gradual cognitive decline in patients with dementia. There may also be a family history of dementia.
INVESTIGATIONS
Screening cognitive assessments such as the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MOCA).
Mood disorders with psychosis
SIGNS / SYMPTOMS
The history often provides sufficient information to help differentiate between schizoaffective disorder and mood disorders with psychosis. In mood disorder with psychosis, the mood disorder usually precedes the psychosis, and the psychosis normally begins as the mood symptoms increase and psychosis remits when mood symptoms decrease.
INVESTIGATIONS
No differentiating tests.
Malingering and factitious disorders
SIGNS / SYMPTOMS
In malingering, there is an identifiable material secondary gain. In factitious illness, patients may need constant reassurance and attention and, as a result, consciously or unconsciously feign symptoms of illness. In the initial diagnostic interview, particular attention needs to be paid to inconsistency in the history provided to atypical presentations and to evasiveness on the part of the patient when asked for details of particular symptoms.
INVESTIGATIONS
No differentiating tests.
Delusional disorder
SIGNS / SYMPTOMS
A condition that presents with circumscribed delusions in the absence of hallucinations, thought disorders, or affective flattening. If mood episodes occur they are relatively brief, and patients do not meet diagnostic criteria for schizoaffective disorder.[1]
INVESTIGATIONS
No differentiating tests.
Brief psychotic disorder
SIGNS / SYMPTOMS
Short duration of psychosis (<1 month) not accompanied by functional deterioration of 6 months or more.
INVESTIGATIONS
No differentiating tests.
Medical and neurologic conditions
SIGNS / SYMPTOMS
Numerous conditions can mimic psychiatric symptoms. Some of the conditions that can affect the brain and cause psychosis are: epilepsy, tumors (not only brain tumors), HIV, neurosyphilis, pellagra, vitamin B12 deficiency, herpes encephalitis, and Wilson disease.
INVESTIGATIONS
Laboratory studies help to differentiate, such as rapid plasma reagin (RPR), HIV tests, herpes simplex virus polymerase chain reaction (HSV-PCR) in cerebrospinal fluid, copper urine levels, ceruloplasmin in blood, and vitamin B12 levels.
Heavy metal poisoning
SIGNS / SYMPTOMS
Short duration: psychosis due to heavy metals (e.g., bromide, mercury) appears days or weeks after exposure.
A careful history should be taken, looking for possible toxic exposure. Psychosis may present suddenly, and when exposure is treated, symptoms will remit.
INVESTIGATIONS
Toxic screen for bromide or mercury level may be performed in the emergency department. A serum bromide test >50 mg/dL is positive for bromide toxicity. A mercury level >20 micrograms/L is considered toxic.
Medication-induced psychosis
SIGNS / SYMPTOMS
Some patients are more susceptible than others to develop psychosis and confusion with prescribed medications. Review of patient's medications, including over-the-counter products, is mandatory.
Steroids, anticholinergic agents, disulfiram, digitalis, and L-dopa are the most notorious for causing psychosis in predisposed patients.
INVESTIGATIONS
Quantitative levels of medication (e.g., digitalis) should be measured if available.
Carbon monoxide poisoning
SIGNS / SYMPTOMS
Psychosis due to carbon monoxide usually occurs within days to weeks of exposure. A careful history should be taken, looking for possible toxic exposure.
INVESTIGATIONS
Toxic screen for carboxyhemoglobin may be performed in the emergency department.
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