What are the criteria to diagnose psychosis in a patient of any age with a history of psychiatric conditions, substance abuse, or neurological disorders, presenting with symptoms such as hallucinations, delusions, and disorganized thinking?

Diagnostic Criteria for Psychosis

Psychosis is diagnosed when at least two of the following symptoms are present for a significant period during a 1-month period: delusions, hallucinations, disorganized speech, grossly disorganized or catatonic behavior, and negative symptoms 1. However, only one symptom is required if delusions are bizarre, hallucinations include a running commentary, or two or more voices are conversing 1.

Core Symptom Requirements

The diagnosis requires:

• Duration: Symptoms must persist for at least 6 months, including an active phase with or without prodromal/residual phases 1
• Functional decline: Marked deterioration in functioning below the level achieved before onset, including failure to achieve age-appropriate interpersonal, academic, or occupational development in children and adolescents 1
• Consciousness: Unlike delirium, awareness and level of consciousness remain intact in psychosis—this is a critical distinguishing feature 2, 3, 1

Essential Exclusion Criteria Before Diagnosis

You must systematically rule out secondary causes before diagnosing a primary psychotic disorder 4:

Medical Conditions to Exclude

• Delirium (most common cause in elderly): characterized by inattention, fluctuating consciousness, and acute onset over hours to days 2
• CNS lesions: brain tumors, congenital malformations, head trauma 4
• Seizure disorders: including nonconvulsive status epilepticus and postictal states 4, 2
• Neurodegenerative disorders: Huntington's chorea, lipid storage disorders 4
• Metabolic disorders: endocrinopathies, Wilson's disease 4, 2
• Infectious diseases: encephalitis, meningitis, HIV-related syndromes 4, 2
• Autoimmune diseases: autoimmune encephalitis 2
• Cerebrovascular disease: stroke may present with psychotic symptoms, particularly in elderly 2

Substance-Related Causes to Exclude

• Toxic encephalopathies: amphetamines, cocaine, hallucinogens, phencyclidine, alcohol, marijuana, solvents 4
• Medication-induced: stimulants, corticosteroids, anticholinergic agents 4
• Withdrawal states: require immediate benzodiazepine treatment to prevent seizures 2
• If psychotic symptoms persist longer than one week despite documented detoxification, consider primary psychotic disorder rather than substance-induced psychosis 4

Psychiatric Conditions to Exclude

• Schizoaffective disorder 1
• Mood disorders with psychotic features: bipolar disorder with psychosis presents with marked euphoria, grandiosity, irritability, racing thoughts, increased psychomotor activity, mood lability, and marked sleep disturbance 3. In adolescents, mania frequently presents with florid psychosis including hallucinations, delusions, and thought disorder 4, 3
• Psychotic depression: may present with mood-congruent or incongruent psychotic features 4

Required Diagnostic Workup

History and Physical Examination

• Collateral history from family: essential for establishing presentation and course of illness 5
• Recent head injury or trauma, seizures, cerebrovascular disease, new or worsening headaches 5
• Substance use history: comorbid substance abuse occurs in up to 50% of adolescents with schizophrenia 4
• Family psychiatric history: helpful differentiating factor, though increased family history of depression also found in schizophrenic youth 4
• Complete neurologic and mental status assessments 5
• Vital signs: tachycardia or severe hypertension may indicate drug toxicity or thyrotoxicosis; fever may suggest encephalitis or porphyria 5

Laboratory Testing

Basic medical evaluation should include 4:

• Complete blood count
• Serum chemistry studies
• Thyroid function analyses
• Urinalysis
• Toxicology screens
• HIV testing if risk factors present 4
• Additional tests to consider: parathyroid hormone, calcium, vitamin B12, folate, niacin 5
• Chromosomal analysis if clinical features suggest developmental syndrome (e.g., velocardiofacial syndrome) 4

Neuroimaging Indications

Neuroimaging with CT or MRI is indicated when 2:

• Focal neurological deficits present
• History of head trauma
• Atypical features
• New-onset psychosis in elderly patients
• First episode psychosis with neurological signs
• Evidence of neurological dysfunction warrants consideration of neuroimaging studies, electroencephalogram, and/or neurology consultation 4

Critical Clinical Pitfalls

• Missing delirium doubles mortality: Always evaluate for fluctuating consciousness, disorientation, and inattention (delirium) versus intact awareness (psychosis) 2
• Misdiagnosis between bipolar disorder and schizophrenia: Historically, approximately one-half of adolescents with bipolar disorder were originally misdiagnosed as having schizophrenia 4. Bipolar disorder tends to have a cyclical course, which helps differentiate it from schizophrenia 3
• Overlooking withdrawal states: These require immediate benzodiazepine treatment to prevent seizures 2
• Nonpsychotic youth misdiagnosed with psychosis: Youth with conduct and other nonpsychotic emotional disorders may report psychotic-like symptoms but have lower rates of negative symptoms, bizarre behavior, and thought disorder compared to truly psychotic children 4
• Longitudinal reassessment is essential: Discriminating among various disorders may be difficult at initial presentation, and periodic diagnostic reassessments are always indicated 4

Age-Specific Considerations

Children and Adolescents

• Symptom presentations vary from classic adult descriptions 3
• Irritability, belligerence, and mixed manic-depressive features are more common than euphoria in children 3
• Peer or romantic conflicts may be precipitants of psychotic symptoms 2
• Negative symptoms may be mistaken for depression 4

Elderly Patients

• Delirium is the most common cause of psychotic symptoms in elderly presenting to emergency departments, with infection being a common precipitating factor 2
• Dementia-related psychosis represents a distinct clinical entity 2