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Difficulty: MediumPhysical Examination Findings

A 64-year-old man is brought to the outpatient clinic by his daughter due to worsening confusion, inverted sleep-wake cycles, and forgetfulness over the past week. His medical history is notable for compensated cirrhosis secondary to chronic hepatitis C viral infection. His vital signs are within normal limits. During the physical examination, the physician asks the patient to extend his arms forward with his wrists dorsiflexed and fingers spread apart. After a few seconds, the patient exhibits brief, rapid, arrhythmic, downward lapses of both hands, followed by a quick return to the original extended position. Which of the following is the most accurate clinical interpretation of this specific physical examination finding?

  1. It represents a failure to maintain sustained motor posture secondary to a metabolic encephalopathy.Answer
  2. B
    Its severity can be reliably calculated by interpreting isolated elevations in venous ammonia levels.
  3. C
    It is a focal upper motor neuron sign that necessitates immediate magnetic resonance imaging of the brain.
  4. D
    It confirms a primary neurodegenerative resting tremor, making further investigation of his altered mentation unnecessary.
  5. E
    It indicates a central nervous system infection, requiring an invasive lumbar puncture before non-invasive metabolic testing.

Answer

The described physical finding is asterixis, which indicates a failure to maintain sustained motor posture and is a classic sign of metabolic encephalopathy.
The patient exhibits asterixis, which is defined as negative myoclonus—a brief, arrhythmic loss of sustained muscle tone. When the wrists are actively dorsiflexed, this presents as a 'flapping' motion. In a patient with cirrhosis, altered sleep-wake cycles, and confusion, this specific physical examination finding strongly points to hepatic encephalopathy, a type of metabolic encephalopathy.

Step-by-Step Solution

1
Identify the physical examination finding described in the vignette.
The rapid, arrhythmic downward lapses of dorsiflexed wrists is known as asterixis or a 'flapping tremor'.
Recognizing the physical sign is the first step to determining its underlying pathophysiology and clinical significance.
2
Correlate asterixis with the patient's underlying medical history and acute presentation.
The patient has a history of cirrhosis and new-onset confusion, which strongly points toward hepatic encephalopathy.
Asterixis is a hallmark physical finding of metabolic encephalopathies, most commonly hepatic, uremic, or hypercapnic in origin.
3
Evaluate the options based on the established pathophysiology of the physical sign.
Asterixis is a form of negative myoclonus (brief loss of muscle tone) caused by metabolic disturbances, rather than a focal structural lesion, an infectious process, or a primary neurodegenerative disease.
This confirms that the finding represents a failure of sustained motor posture secondary to metabolic encephalopathy.

Key Concept

Asterixis is a clinical sign of metabolic encephalopathy characterized by an inability to maintain a sustained motor posture (negative myoclonus), often seen in hepatic encephalopathy, uremia, and hypercapnia.
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Physical Examination Findings

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