Medical Student (MS3) Neurosurgery, Baylor College of Medicine Houston, TX, US
Introduction: DBS is an effective therapy for treatment-resistant obsessive compulsive disorder (trOCD), achieving a success rate of 66%. Here, we document instances of phantosmia in patients receiving DBS targeting the ventral capsule/ventral striatum (VC/VS) region and explore potential underlying mechanisms.
Methods: We conducted a review of intraoperative and subsequent programming records of 23 patients who received DBS for trOCD between 2018 and 2024 at our institution. We interviewed those with a history of phantosmia to obtain insights into these phenomena. We reconstructed electrode placements in MNI152 space to investigate their proximity to nearby olfactory structures, namely the primary olfactory cortex (OC) and the anterior commissure (AC). We compared distance to those structures between patients with and without a history of phantosmia. Finally, we calculated the volumes of tissue activated (VTAs) during documented instances of phantosmia and investigated their overlap with the OC and AC.
Results: Five patients reported phantosmia during intraoperative and/or follow-up programming sessions. These experiences were transient and arose after DBS parameter changes. Olfactory experiences included smelling “burning cinnamon”, an “organic chemistry lab”, “medical gas”, and “bad smell”. Contact points associated with olfactory phenomena were significantly closer to the anterior commissure than nonolfactory contacts (p=0.01), but not the olfactory cortex (p=0.07). Additionally, VTAs consistently overlapped with the AC during phantosmia, but not the olfactory cortex.
Conclusion : The AC is known to carry olfactory fibers from the olfactory bulb and cortex to the contralateral hemisphere. Our retrospective study documents transient phantosmia as a side effect arising from stimulation adjustments and suggests a potential mechanism: via stimulation of olfactory fibers in the AC.
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