Stimulation induced hypogeusia in thalamic deep brain stimulation for tremor: an underestimated yet common side effect

Recently, stimulation-induced hypogeusia in thalamic deep brain stimulation (DBS) for essential tremor has been described in two case reports,1 ,2 suggesting an exceptional occurrence. Surprisingly, an inquiry among 16 patients with thalamic DBS revealed that half of them suffered from stimulation-induced hypogeusia. We hypothesise that the distance between the volume of activated tissue (VAT) and the assumed course of gustatory fibres determines the manifestation of this side effect. We expect to observe shorter distances or even an overlap in patients with stimulation-induced hypogeusia, and a correlation between these distances and the gustometry performance. Informed consent was obtained from the 16 patients, who suffered from essential tremor (11), tremor-dominant Parkinson’s disease (3) or dystonic head tremor (2), respectively. Two patients with a tremor-dominant Parkinson’s disease had received a unilateral DBS-system. None of the patients reported taste disturbances prior to DBS implantation. Six patients refused to take part in the gustometry. The medial lemniscus (ML) and dentato-rubro-thalamic tract (DRT) were determined tractographically in relation to effective electrode contact positions, and the surrounding electric field was visualised as VAT (figure 1A–C). For details regarding imaging, tractography and calculation of electric fields, please refer to our previous publication.3 The gustatory pathway is not traceable tractographically due to its small volume and curved course. However, the human gustatory tract between the nucleus of the solitary tract and the thalamic ventral posteromedial nucleus has been defined by lesion cases, suggesting a course adjacent to the medial margin of the ML at their entrance into the thalamus.4 Thus we used the position of the medial margin of the ML as a substitute measurement for the position of the gustatory tract in this …