A 62-year-old man with Parkinson disease on levodopa monotherapy for 4 years presents with motor fluctuations and "on-off" phenomena. His morning dose provides only 2 hours of benefit, and he experiences severe bradykinesia in the afternoon. Cognitive function and blood pressure are normal. What is the most appropriate next step in management?

Explanation

## Management of Motor Fluctuations in Parkinson Disease ### Clinical Context This patient has developed **wearing-off** (end-of-dose deterioration) after 4 years on levodopa monotherapy—a predictable complication of long-term dopaminergic therapy. The key is to optimize dopaminergic delivery before considering invasive interventions. ### Stepwise Approach to Motor Fluctuations **Key Point:** Motor fluctuations in PD follow a predictable timeline: initial stable response → wearing-off → on-off dyskinesias. Management escalates through pharmacological optimization before surgery. | Stage | Clinical Feature | Management Strategy | |-------|------------------|---------------------| | Early | Stable 4–6 hr benefit | Monotherapy sufficient | | Intermediate | Wearing-off (2–3 hr benefit) | Increase frequency/dose; add COMT-I or MAO-B-I | | Advanced | Unpredictable on-off; dyskinesias | Consider DBS if cognitive/motor criteria met | ### Rationale for Correct Answer 1. **Increase levodopa dose and frequency** → Extends the duration of each dose's benefit by achieving higher peak plasma levels and reducing the time below therapeutic threshold. 2. **Add a COMT inhibitor** (entacapone, tolcapone) → Blocks peripheral catechol-O-methyltransferase, prolonging levodopa half-life from ~90 min to ~150 min, effectively extending the "on" period by 1–2 hours. 3. **Why not MAO-B inhibitors alone?** Selegiline/rasagiline provide modest symptomatic benefit (~20% improvement) but are insufficient as monotherapy for established wearing-off; they are better used as adjuncts or in early disease. **Clinical Pearl:** COMT inhibitors are the evidence-based choice for wearing-off in patients already on levodopa, as they directly prolong levodopa availability without introducing a new drug class. ### Why DBS Is Premature DBS is reserved for: - Failure of optimal medical therapy (≥5 medication trials) - Cognitive impairment absent (MMSE >24) - Disease duration >4 years AND motor complications present This patient has not yet exhausted pharmacological options and has normal cognition, so surgery is not the next step. **High-Yield:** The sequence is: optimize levodopa dose → add COMT-I or MAO-B-I → consider DBS only after medical failure. [cite:Harrison 21e Ch 428]