A 27-year-old man is brought to the emergency department by his sister due to increasingly… — USMLE Step 2 CK

A $27$ -year-old man is brought to the emergency department by his sister due to increasingly bizarre behavior over the past $6$ weeks. The sister reports that he has been barring the doors to their apartment, claiming that intelligence agencies have placed listening devices in the walls. He has also been talking to himself and appears to be responding to unseen stimuli. Over the past three days, he has not slept. He has no prior psychiatric history. His temperature is $37.7^\circ\text{C}$ ( $99.9^\circ\text{F}$ ), pulse is $118/\text{min}$ , and blood pressure is $152/94\text{ mm Hg}$ . Physical examination reveals a thin, disheveled man. He is diaphoretic and has prominent dental caries along with multiple healing excoriations on his bilateral forearms and face. He is hypervigilant and frequently paces the room. Which of the following is the most likely diagnosis?

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

Answer

Substance-induced psychotic disorder

The correct answer accurately identifies that this patient's psychosis is a direct physiological consequence of substance abuse. Although the patient's severe paranoia and auditory hallucinations represent a psychotic state, the physical examination provides critical clues pointing to an underlying etiology. The combination of marked sympathetic hyperactivity (tachycardia, hypertension, diaphoresis), severe dental caries ('meth mouth' due to bruxism and decreased saliva production), and healing skin excoriations (resulting from delusional parasitosis, or 'meth bugs') is highly characteristic of chronic methamphetamine abuse. According to diagnostic criteria, a primary psychiatric diagnosis can only be made if the condition is not attributable to the physiological effects of a substance.

Step-by-Step Solution

Identify the primary psychiatric syndrome.

The patient presents with auditory hallucinations, delusions of persecution, and severe agitation, establishing a psychotic state.

Characterizing the core symptoms focuses the differential diagnosis on primary psychotic disorders versus secondary etiologies.

Evaluate the timeline of the symptoms.

The symptoms have been present for

6

weeks.

In the absence of secondary causes, a

6

-week duration of psychosis points toward schizophreniform disorder (which spans

1

6

months).

Analyze the physical examination and vital signs for secondary causes.

The patient has marked sympathetic overactivity (tachycardia, hypertension, diaphoresis), decreased need for sleep, extensive dental caries, and skin excoriations.

These physical findings strongly indicate chronic methamphetamine intoxication (meth mouth, tactile hallucinations leading to excoriations).

Synthesize the diagnostic criteria.

Because the psychotic symptoms occur in the context of physiological evidence of substance abuse, primary psychiatric diagnoses are excluded.

DSM-5 diagnostic criteria for primary psychotic disorders strictly require that symptoms are not attributable to the physiological effects of a substance.

Key Concept

Differentiating primary psychotic disorders from substance-induced psychotic disorders based on physical examination findings.

Estimated Time:1m 30s

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