Dysosmia in PD (Parkinson’s Disease) may result from changes in the olfactory apparatus or in structures involved in olfactory perception. Previous work1,2 has suggested that deep brain stimulation (DBS) pa-tients have improved odor discrimination in stimulation-on/medication-off state in comparison to their own scores in a stimulation-off/medication-off state. What remains unclear is whether it is the ON state itself or an effect of stimulation that leads to improved olfaction. In this study we evaluate dysosmia in two PD cohorts in the ON state, those treated with medication alone and those treated with medication and DBS.

A prospective study geared at improving predictive value of olfactory testing with a battery of psychological tests enrolled 45 PD patients and 44 controls. Of the PD patients, 9 had bilateral STN (subthalamic nucleus) DBS and 36 were medically treated. Subset analysis of PD patients with and without DBS placement revealed no difference in apathy or depression. DBS patients had better olfaction on UPSIT (Univ of Pennsylvania Smell Identification Test) (p

This study provides further data that DBS patients have improved ol-faction. It also provides preliminary evidence that DBS with medica-tion improves dysosmia to a greater extent than medication alone. This may result from indirect stimulation of olfactory processing cen-ters or changes in olfactory circuitry metabolism.