A 68-year-old man is brought to the emergency department by his wife due to severe muscle … — USMLE Step 2 CK

A $68$ -year-old man is brought to the emergency department by his wife due to severe muscle stiffness, fever, and marked confusion over the past $48$ hours. Over the past $14$ months, the patient has experienced progressive cognitive decline, prominent day-to-day fluctuations in alertness, and vivid, recurrent visual hallucinations of people in his house. His wife notes that he often thrashes and punches his pillows while asleep. His past medical history is significant for major depressive disorder. Current medications include a daily multivitamin and citalopram. Three days ago, a covering physician prescribed haloperidol to manage the patient's distressing hallucinations. On examination, his temperature is $39.4^\circ\text{C}$ ( $102.9^\circ\text{F}$ ), pulse is $118\text{ /min}$ , and blood pressure is $168/102\text{ mm Hg}$ . He is diaphoretic and disoriented. Neurologic examination reveals profound "lead-pipe" muscle rigidity in all extremities. Deep tendon reflexes are $1+$ bilaterally, and there is no clonus. Laboratory studies show a creatine kinase of $4,500\text{ U/L}$ , a TSH of $3.5\text{ mU/L}$ (normal: $0.5-5.0\text{ mU/L}$ ), and a free T4 of $1.2\text{ ng/dL}$ (normal: $0.9-1.7\text{ ng/dL}$ ). Which of the following is the most likely cause of this patient's acute presentation?

A
Toxic accumulation of intrasynaptic serotonin
Extreme sensitivity to dopamine antagonismAnswer
C
Late-onset primary psychotic disorder
D
Unrecognized primary hypothyroidism
E
Antidepressant-induced manic switch

Answer

Extreme sensitivity to dopamine antagonism

The patient's 14-month history of fluctuating cognition, recurrent visual hallucinations, and REM sleep behavior disorder is the classic triad for Major Neurocognitive Disorder with Lewy Bodies (LBD). A key clinical feature of LBD is severe sensitivity to dopamine antagonists (particularly typical antipsychotics like haloperidol). Administering these medications to a patient with LBD can rapidly precipitate Neuroleptic Malignant Syndrome (NMS). NMS is a life-threatening neurologic emergency characterized by the tetrad of altered mental status, autonomic instability (fever, tachycardia, hypertension), 'lead-pipe' muscle rigidity, and elevated creatine kinase. Therefore, extreme sensitivity to dopamine antagonism is the underlying cause of this patient's acute deterioration.

Step-by-Step Solution

Diagnose the underlying neurocognitive disorder based on the 14-month history.

The combination of progressive cognitive decline, fluctuating alertness, visual hallucinations, and REM sleep behavior disorder strongly points to Major Neurocognitive Disorder with Lewy Bodies (LBD).

Establishing the correct type of dementia is crucial for understanding medication contraindications.

Analyze the recent medication change and its interaction with the underlying disease.

The patient was recently prescribed haloperidol, a typical antipsychotic (dopamine antagonist).

Patients with LBD have a well-documented, severe sensitivity to neuroleptic medications.

Evaluate the acute clinical signs and laboratory findings.

Fever, tachycardia, hypertension, diaphoresis, extreme 'lead-pipe' rigidity, normal/decreased reflexes, and significantly elevated creatine kinase indicate Neuroleptic Malignant Syndrome (NMS).

The clinical picture perfectly matches NMS, which was precipitated by the administration of a dopamine antagonist in a highly susceptible LBD patient.

Key Concept

Patients with Lewy Body Dementia exhibit severe sensitivity to typical antipsychotics (dopamine antagonists), which can rapidly precipitate potentially fatal Neuroleptic Malignant Syndrome (NMS).

Estimated Time:1m 30s

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