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Difficulty: MediumNeurocognitive Disorders

A 74-year-old woman is brought to the emergency department from her home by her daughter due to severe confusion and agitation that began yesterday. The daughter reports that the patient was previously able to manage her daily activities but has been 'talking to people who aren't there' and pacing the house incessantly over the past 24 hours. The patient has a history of major depressive disorder and mild cognitive impairment. Two days ago, she developed a runny nose and began taking an over-the-counter cold and allergy medication. Her prescribed medications include daily citalopram. Routine laboratory results from a clinic visit one week ago showed a decreased free thyroxine (T4) level with a normal thyroid-stimulating hormone (TSH) level. On physical examination, her temperature is 37.8°C (100.0°F), pulse is 112/min, and blood pressure is 142/86 mm Hg. She is disoriented to place and time. Her skin is warm, flushed, and dry. Her pupils are 7 mm bilaterally and sluggishly reactive to light. Bladder ultrasound reveals 600 mL of retained urine. Which of the following is the most likely cause of this patient's acute presentation?

  1. A
    Excessive central serotonergic activity
  2. B
    Medication-induced manic episode
  3. C
    Acute primary psychotic episode
  4. Anticholinergic medication toxicityAnswer
  5. E
    Undiagnosed secondary hypothyroidism

Answer

Anticholinergic medication toxicity
The correct answer is anticholinergic medication toxicity. This patient is presenting with acute-onset delirium characterized by confusion, agitation, and visual hallucinations. When combined with her physical examination findings—tachycardia, hyperthermia, dry and flushed skin, mydriasis (dilated pupils), and urinary retention—the clinical picture perfectly matches the anticholinergic toxidrome ('mad as a hatter, blind as a bat, red as a beet, hot as a hare, dry as a bone, full as a flask'). Elderly patients, particularly those with underlying mild cognitive impairment or dementia, are extremely sensitive to the central effects of anticholinergic drugs. Over-the-counter cold and allergy medications frequently contain first-generation antihistamines (such as diphenhydramine or chlorpheniramine) which have potent antimuscarinic properties.

Step-by-Step Solution

1
Identify the primary clinical syndrome from the patient's history.
The patient presents with acute-onset confusion, agitation, and visual hallucinations.
Recognizing the acute, fluctuating nature of the cognitive decline establishes the diagnosis of delirium.
2
Analyze the physical examination findings to identify an underlying etiology.
The patient exhibits tachycardia, low-grade fever, dry and flushed skin, dilated and sluggish pupils, and urinary retention.
These findings represent a specific toxidrome that must be matched to a pharmacological or physiological cause.
3
Correlate the toxidrome with the patient's recent medication history.
The combination of delirium and these autonomic signs is the classic presentation of anticholinergic toxicity, likely triggered by the recent use of an over-the-counter cold and allergy medication (which typically contain first-generation antihistamines).
Elderly patients with baseline cognitive impairment are highly susceptible to the central nervous system effects of anticholinergic medications.

Key Concept

Anticholinergic toxicity presents with delirium, hyperthermia, tachycardia, dry flushed skin, mydriasis, and urinary retention, and is a common cause of acute neurocognitive decline in the elderly.
Estimated Time:1m 30s
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Topics

Neurocognitive Disorders

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