An 82-year-old man arrives at the emergency department accompanied by his daughter due to … — USMLE Step 2 CK

An 82-year-old man arrives at the emergency department accompanied by his daughter due to severe agitation, disorientation, and visual hallucinations that began acutely $48$ hours ago. He repeatedly points to the corner of the room, claiming that intruders are hiding there. His daughter notes that over the past $3$ years, he has developed mild forgetfulness, such as occasionally misplacing his keys, but he has always remained independent in his daily activities. His medical history includes hypertension, osteoarthritis, and major depressive disorder. His daily medications include lisinopril and fluoxetine. Two weeks ago, he was prescribed tramadol for worsening knee pain. Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure of $130/80\text{ mmHg}$ , and a heart rate of $82\text{/min}$ . Physical examination reveals no focal neurologic deficits, normal muscle tone, and absent clonus. He is unable to recite the months of the year backward. Laboratory testing reveals a thyroid-stimulating hormone (TSH) level of $2.1\text{ }\mu\text{U/mL}$ (normal: $0.5-5.0\text{ }\mu\text{U/mL}$ ) and free thyroxine (T4) of $1.2\text{ ng/dL}$ (normal: $0.9-2.4\text{ ng/dL}$ ). Urinalysis is positive for leukocyte esterase, nitrites, and numerous leukocytes. What is the most accurate diagnosis for this patient's current presentation?

A
Serotonin syndrome
B
Brief psychotic disorder
Delirium due to another medical conditionAnswer
D
Substance/medication-induced bipolar and related disorder
E
Psychotic disorder due to hypothyroidism

Answer

The most accurate diagnosis is delirium due to another medical condition.

The patient presents with an acute onset of fluctuating attention, disorientation, and visual hallucinations. In an elderly patient with a history of mild underlying cognitive decline, these findings are hallmark features of delirium. The positive urinalysis indicates a urinary tract infection, which is a highly common precipitant of delirium in this age group. The inability to recite the months of the year backward demonstrates the core deficit of inattention.

Step-by-Step Solution

Identify the core clinical syndrome based on the time course and mental status examination.

The patient has an acute onset (

48

hours) of fluctuating attention (inability to recite months backward), disorientation, and visual hallucinations.

Establishing the primary syndrome narrows the differential diagnosis to acute neurocognitive disorders (delirium) versus primary psychiatric illnesses.

Evaluate the medical context and diagnostic test results to identify an underlying etiology.

The patient has a positive urinalysis indicative of a urinary tract infection (UTI) and normal vital signs without neuromuscular hyperreactivity.

Identifying an underlying systemic illness (UTI) explains the acute cognitive changes, confirming a diagnosis of delirium and ruling out medication-induced toxidromes like serotonin syndrome.

Key Concept

Delirium is an acute, fluctuating neurocognitive disorder characterized by inattention and disorganized thinking or altered level of arousal, most commonly triggered by an underlying medical condition such as an infection in elderly patients.

Estimated Time:1m 30s

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