Unilateral asterixis associated with a mesencephalic syndrome

Area of Science:

• Neurology
• Neuroscience
• Clinical Electrophysiology

Background:

• Asterixis, characterized by sudden, brief, irregular muscle jerks, is typically associated with metabolic encephalopathies.
• Focal brain lesions causing unilateral asterixis are exceptionally rare in clinical practice.

Observation:

• A patient presented with acute asterixis exclusively affecting the left upper extremity.
• The asterixis occurred alongside signs of acute midbrain dysfunction.
• Crucially, the patient exhibited no alterations in mental status or electroencephalogram (EEG) findings, and no metabolic or toxic disturbances were identified.

Findings:

• Electromyography (EMG) revealed electrophysiological characteristics consistent with asterixis typically seen in metabolic etiologies.
• Despite the EMG findings, the clinical presentation pointed towards a focal structural lesion in the brain, specifically the midbrain.

Implications:

• This case challenges the conventional understanding of asterixis as solely a marker of metabolic disturbances.
• It underscores the importance of considering focal brain lesions, particularly in the midbrain, as a potential cause of unilateral asterixis.
• The findings suggest that EMG alone may not be sufficient to differentiate metabolic from structural causes of asterixis in all instances.