Yawning in Parkinson's disease

To the Editor: We read with interest the Clinical/Scientific Note by Drs. Goren and Friedman1 on levodopa-induced yawning in PD. They state that “yawning has not been associated with treated or untreated PD,” and they suggest that “if yawning is a dopamine-mediated phenomenon in humans it should be seen in PD patients treated with levodopa and dopamine agonists.”1 Indeed, this is the case. It is well known that apomorphine, a direct D1–D2 dopamine receptor agonist, frequently induces yawning just before the onset of the motor effect, both in experimental animals and in patients with PD.2 Yawning was clearly described since the early clinical trials with apomorphine in the 1950s.3,4 More recently this effect was confirmed in the larger clinical series that have marked the revival of this drug as an adjunct therapy for advanced PD, either as intermittent boluses or as a continuous subcutaneous infusion via portable minipumps.5 Interestingly, the widespread reintroduction of apomorphine in the therapeutic arsenal for PD is due to the observation that pretreatment with the peripheral dopamine receptor blocking agent domperidone could prevent apomorphine-induced nausea, drowsiness, and arterial hypotension, but not yawning.6 …