A 22-year-old male university student is escorted to the urgent care clinic by campus secu… — USMLE Step 2 CK

A 22-year-old male university student is escorted to the urgent care clinic by campus security after he was observed shouting at pedestrians and claiming that invisible drones were tracking his movements. His roommate mentions that the patient attended a rave three days ago and has not slept since. The patient's past medical records show a diagnosis of major depressive disorder, for which he is prescribed daily fluoxetine. Vital signs include a heart rate of 128/min, respiratory rate of 20/min, and blood pressure of 162/98 mm Hg. Physical assessment reveals profuse sweating, bilateral mydriasis, and extensive scratch marks on both arms. The patient states he is trying to remove "parasites" from his skin. Assessment of his reflexes shows 2+ patellar responses bilaterally with no evidence of rigidity or clonus. Which of the following is the most likely diagnosis?

A
Brief psychotic disorder
B
Serotonin syndrome
Substance-induced psychotic disorderAnswer
D
Schizophreniform disorder
E
Bipolar I disorder, manic episode

Answer

Substance-induced psychotic disorder

The correct answer is substance-induced psychotic disorder. This patient's presentation of severe paranoia, delusions, and tactile hallucinations (feeling 'parasites' under the skin, leading to excoriations) combined with signs of profound sympathetic overactivity (tachycardia, hypertension, mydriasis, diaphoresis) and prolonged wakefulness strongly points to severe stimulant intoxication (e.g., methamphetamine, cocaine, or synthetic cathinones). The diagnosis of substance-induced psychotic disorder is applied when prominent hallucinations or delusions develop during or soon after substance intoxication, and the symptoms are not better explained by a primary psychotic or mood disorder.

Step-by-Step Solution

Analyze the patient's psychiatric symptoms and timeline.

The patient exhibits severe acute paranoia, visual and tactile hallucinations, and prolonged wakefulness starting three days ago after attending a rave.

Establishing the nature and duration of symptoms is crucial for differentiating primary psychotic disorders from substance-induced states.

Evaluate the physical examination findings and vital signs.

Findings show marked sympathetic overactivity (tachycardia, hypertension, diaphoresis, mydriasis) and skin excoriations from formication, with normal reflexes.

Physical signs help identify specific toxidromes and rule out interacting medication syndromes.

Synthesize the findings to form a diagnosis.

The combination of acute psychosis, tactile hallucinations ('parasites' under the skin), and sympathetic overactivity following a rave is classic for stimulant (e.g., methamphetamine or synthetic cathinones) intoxication, making substance-induced psychotic disorder the most likely diagnosis.

Substance-induced psychotic disorder is diagnosed when prominent hallucinations or delusions occur during or soon after intoxication, and are not better explained by a primary psychiatric disorder.

Rule out alternative diagnoses.

Serotonin syndrome is excluded by the lack of clonus or hyperreflexia. Primary psychotic disorders are excluded by the direct physiological link to the ingested substance.

Confirming the diagnosis requires ensuring alternative conditions are incompatible with the clinical picture.

Key Concept

Stimulant intoxication (e.g., methamphetamine, synthetic cathinones) typically presents with profound sympathetic overactivity, prolonged wakefulness, and can precipitate a substance-induced psychotic disorder characterized by intense paranoia and tactile hallucinations (formication).

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