A 21-year-old man is brought to the emergency department by his roommates because he has b… — USMLE Step 2 CK

A $21$ -year-old man is brought to the emergency department by his roommates because he has been acting increasingly erratic and paranoid over the last $48$ hours. He barricaded himself in his bedroom, claiming that foreign spies are broadcasting signals into his brain through the smoke detector. His roommates report that he has no prior psychiatric history but has been staying awake for the past three nights studying for final exams, consuming large amounts of a "study aid" powder he bought from an unverified website. On examination, the patient is highly agitated, pacing the room, and sweating profusely. Vital signs are temperature $37.8^\circ \text{C}$ ( $100.0^\circ \text{F}$ ), blood pressure $162/98$ mmHg, pulse $124$ /min, and respirations $20$ /min. Pupillary examination reveals bilateral mydriasis. Which of the following is the most likely diagnosis?

Substance-induced psychotic disorderAnswer
B
Brief psychotic disorder
C
Schizophreniform disorder
D
Schizophrenia
E
Delusional disorder

Answer

Substance-induced psychotic disorder

The patient's presentation of acute-onset paranoia, delusions, and severe agitation following the consumption of an unknown 'study aid' powder is highly characteristic of stimulant intoxication (e.g., amphetamines, synthetic cathinones). This diagnosis is strongly supported by the physical examination findings of sympathetic hyperactivity, including tachycardia, hypertension, diaphoresis, and mydriasis. Because the psychotic symptoms emerged during or shortly after the substance intoxication, and the physical exam confirms the intoxication state, the most appropriate diagnosis is substance-induced psychotic disorder. Diagnosing any primary psychotic condition requires ensuring the symptoms are not due to the physiological effects of an exogenous substance.

Step-by-Step Solution

Analyze the patient's psychiatric symptoms and their onset.

The patient has acute onset of paranoia and delusions beginning over the last 48 hours.

Establishing the timeline of psychiatric symptoms is crucial for differentiating primary psychotic disorders from secondary causes.

Evaluate the patient's physical examination and vital signs.

The patient demonstrates a sympathomimetic toxidrome, including tachycardia, hypertension, diaphoresis, and mydriasis, alongside severe insomnia.

Physical findings provide objective evidence of acute substance intoxication (e.g., stimulants like amphetamines or synthetic cathinones).

Synthesize the findings to determine the correct diagnosis.

The combination of acute psychosis and a sympathomimetic state following the ingestion of a powder points to a substance etiology rather than a primary psychiatric illness.

A primary psychiatric diagnosis can only be made when the symptoms are not directly attributable to the physiological effects of a substance or another medical condition.

Key Concept

Substance-induced psychotic disorder occurs when prominent hallucinations or delusions arise during or soon after substance intoxication or withdrawal, and the clinical picture is supported by physical signs of that intoxication.

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