A 55-year-old man has Parkinson's disease treated with levodopa-carbidopa for 6 years. He now develops involuntary writhing movements of his limbs occurring 60–90 minutes after each dose. These represent:

• A Wearing-off phenomenon (end-of-dose deterioration)
• B Peak-dose dyskinesias (choreiform movements at maximum plasma levodopa level) ✓
• C Diphasic dyskinesias occurring at the onset and offset of the dose effect
• D Off-state dystonia occurring in the early morning

Explanation

Peak-dose dyskinesias are involuntary choreiform or dystonic movements occurring when plasma levodopa concentrations are at their highest (approximately 60–90 minutes post-dose), corresponding to maximum dopamine receptor stimulation. They are managed by reducing individual levodopa dose (while increasing dose frequency or adding amantadine, which has anti-dyskinetic properties by blocking NMDA receptors). Wearing-off occurs near the end of each dose interval when levodopa levels fall. Diphasic dyskinesias occur at both the beginning and end of the dose response.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.