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Difficulty: EasyFormulating a Differential Diagnosis

A 78-year-old female is evaluated on the inpatient medical ward for acute-onset confusion and agitation. She was admitted two days ago for a mild exacerbation of chronic obstructive pulmonary disease (COPD) and has been receiving nebulized albuterol, systemic corticosteroids, and supplemental oxygen. Last night, she reported insomnia and was administered a dose of over-the-counter oral diphenhydramine. This morning, she is disoriented to place and time, exhibits fluctuating attention, and claims to see insects crawling on her blanket. Her temperature is 37.0°C (98.6°F), blood pressure is 128/78 mm Hg, heart rate is 88/min, and oxygen saturation is 96% on room air. A comprehensive metabolic panel reveals a serum sodium of 134 mEq/L. Urinalysis shows trace bacteriuria but is negative for leukocyte esterase and nitrites. Which of the following should be prioritized at the top of the differential diagnosis for this patient's acute mental status change?

  1. A
    Hyponatremic encephalopathy
  2. Medication-induced deliriumAnswer
  3. C
    Urinary tract infection
  4. D
    Hypoxic encephalopathy
  5. E
    Acute ischemic stroke

Answer

Medication-induced delirium is the most likely diagnosis due to the recent administration of diphenhydramine in an elderly patient.
The correct answer is medication-induced delirium. Diphenhydramine is a first-generation antihistamine with potent anticholinergic properties. In older adults, the clearance of these medications is reduced, and the central nervous system is more sensitive to anticholinergic effects. This frequently leads to acute delirium, classically characterized by disorientation, fluctuating attention, and visual hallucinations (often described as seeing insects or animals). Recognizing this common iatrogenic cause is a critical step in formulating a differential diagnosis for acute mental status changes in hospitalized patients.

Step-by-Step Solution

1
Analyze the patient's presenting symptoms and timeline.
The patient developed acute-onset confusion, fluctuating attention, and visual hallucinations the morning after receiving an oral dose of diphenhydramine.
Establishing the acute nature and timeline of the mental status change helps differentiate delirium from dementia and identifies potential pharmacological triggers.
2
Evaluate the patient's laboratory findings and vital signs.
Vital signs are stable with normal oxygenation. Serum sodium is mildly low (134 mEq/L) and urinalysis shows asymptomatic bacteriuria without inflammation.
To rule out metabolic (hyponatremia), infectious (UTI), and hypoxic etiologies of delirium.
3
Formulate the most likely differential diagnosis based on the synthesis of data.
Medication-induced delirium is prioritized over other causes.
Diphenhydramine is a first-generation antihistamine with strong anticholinergic properties that frequently causes acute delirium in the elderly population.

Key Concept

Older adults are highly susceptible to the anticholinergic adverse effects of medications like diphenhydramine, which frequently manifest as acute delirium with visual hallucinations.
Estimated Time:1m 0s
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Topics

Formulating a Differential Diagnosis

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