Objective: To report a unique case of phantosmia/olfactory hallucinations (OfH) emerging as a non-motor fluctuation after initiation of foslevodopa/foscarbidopa (LDp/CDp) infusion at a lower levodopa equivalent daily dose (LEDD) than prior oral levodopa in Parkinson disease (PD).

Background: Continuous dopaminergic therapies generally improve motor fluctuations in advanced PD; however, non-motor fluctuations, including hallucinations, may be unmasked or altered with continuous stimulation. OfH are a rare non-motor symptom in PD, and their emergence during infusion therapy at a reduced LEDD has not, to our knowledge, been described previously. The relationship between continuous dopaminergic stimulation, reduced LEDD, and the emergence of OfH is poorly defined.

Method: N/A

Results: A 49-year-old man with a 10-year history of akinetic-rigid PD developed disabling motor fluctuations and dyskinesias on oral levodopa/carbidopa and amantadine despite multiple medication adjustments for optimization. He had normal brain imaging and negative comprehensive genetic testing. He declined deep brain stimulation and transitioned to LDp/CDp infusion therapy, delivering a significantly lower LEDD than his prior oral therapy. Shortly after initiating LDp/CDp, he developed episodes of phantosmia involving a pleasant “sweet” smell occurring only during motor fluctuations, particularly when moving from “off” to “on” or into dyskinesia. The episodes last 1–5 minutes and resolve spontaneously. He denies visual, auditory, or tactile hallucinations or baseline anosmia. Following pump titration, he achieved improved motor control (Hoehn & Yahr stage 2 to stage 1) and markedly reduced dyskinesia severity, but the OfH persisted with motor fluctuations.

Conclusion: This case highlights a rare instance of transient OfH linked to motor state transitions after initiation of pLD/pCD therapy at a reduced LEDD. The phenomenon suggests that continuous dopaminergic delivery, rather than absolute dose, may provoke non-visual hallucinosis by altering the striato‑limbic or olfactory networks. Recognition of such dopaminergic state-dependent sensory fluctuations expands our understanding of the non-motor spectrum in advanced PD and highlights the importance of individualized infusion titration, patient counseling, and further research.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-sweet-smell-of-on-phantosmia-during-motor-fluctuations-after-initiation-of-foslevodopa-foscarbidopa-infusion-therapy/