An 80-year-old man with a history of moderate Alzheimer disease and benign prostatic hyper… — USMLE Step 2 CK

An $80$ -year-old man with a history of moderate Alzheimer disease and benign prostatic hyperplasia is brought to the emergency department by his daughter, who is his legally appointed healthcare proxy. Over the past $48$ hours, he has become acutely agitated, disoriented, and has been grasping at invisible objects. Two days ago, he started taking an over-the-counter diphenhydramine preparation for insomnia. The patient's visiting son arrived today and insists the patient be transferred immediately to a psychiatric facility. A recent outpatient urine culture grew $>10^5 \text{ CFU/mL}$ of Escherichia coli sensitive to nitrofurantoin and cephalexin. Recent thyroid tests showed a serum thyroid-stimulating hormone of $1.5 \ \mu\text{U/mL}$ (normal: $0.4-4.0 \ \mu\text{U/mL}$ ) and a free thyroxine of $0.5 \text{ ng/dL}$ (normal: $0.9-2.4 \text{ ng/dL}$ ). Vital signs show a temperature of $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure $135/85 \text{ mm Hg}$ , pulse $108\text{/min}$ , and respirations $16\text{/min}$ . Physical examination reveals dry oral mucosa, flushed skin, and a palpably distended bladder. Which of the following is the most appropriate initial management for this patient?

A
Administration of intravenous piperacillin-tazobactam for the urinary tract infection
B
Initiation of levothyroxine therapy for primary hypothyroidism
Insertion of a urethral catheter and discontinuation of the sleep aidAnswer
D
Initiation of an atypical antipsychotic for schizophreniform disorder
E
Transfer to the psychiatric unit as requested by the patient's son

Answer

The most appropriate initial management is the insertion of a urethral catheter and discontinuation of the sleep aid.

The patient is experiencing acute delirium secondary to anticholinergic toxicity, directly precipitated by the recent use of over-the-counter diphenhydramine. Patients with pre-existing neurocognitive disorders, such as Alzheimer disease, have diminished cognitive reserves and are exquisitely sensitive to the central effects of anticholinergic medications. The patient's clinical picture is a textbook presentation of the anticholinergic toxidrome, which includes altered mental status and hallucinations ('mad as a hatter'), dry mucous membranes ('dry as a bone'), cutaneous vasodilation ('red as a beet'), tachycardia, and urinary retention ('full as a flask'). The urinary retention is further exacerbated by his underlying benign prostatic hyperplasia. The most appropriate initial management is to physically address the acute urinary retention via bladder catheterization and to immediately discontinue the offending pharmacological agent.

Step-by-Step Solution

Analyze the acute clinical presentation.

The patient exhibits acute agitation, visual hallucinations, tachycardia, dry mucosa, flushed skin, and a distended bladder developing over 48 hours.

Identifying the symptom cluster is required to recognize a specific toxicological or medical syndrome.

Correlate symptoms with the recent history.

The symptoms align perfectly with anticholinergic toxicity ('mad as a hatter, dry as a bone, red as a beet, full as a flask') triggered by the initiation of over-the-counter diphenhydramine.

Elderly patients with underlying neurocognitive disorders like Alzheimer disease are highly susceptible to the side effects of anticholinergic medications.

Determine the most immediate medical intervention required.

The palpable bladder indicates acute urinary retention, exacerbated by benign prostatic hyperplasia and the anticholinergic load. This must be relieved immediately.

Acute urinary retention causes severe agitation in cognitively impaired patients and can lead to renal injury if left untreated.

Evaluate and rule out the distracting information.

The psychiatric symptoms are secondary to delirium, not primary psychosis. The UTI is known to be sensitive to narrow-spectrum agents. The thyroid labs indicate central (secondary) hypothyroidism. The son has no legal authority over the appointed proxy.

Ensures the chosen management directly addresses the acute, life-threatening issue without committing clinical or ethical errors.

Key Concept

Diagnosis and management of delirium superimposed on a major neurocognitive disorder due to anticholinergic toxicity and acute urinary retention.

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