Loss of olfaction in de novo and treated Parkinson's disease: Possible implications for early diagnosis

Olfactory dysfunction is a common finding in patients with Parkinson's dise ase (PD). As most studies reported on odor identification in more advanced and treated PD, we administered an odor detection, discrimination, and iden tification test to a heterogeneous. partly de novo, group of patients. Fort y-one non-demented PD patients, 24 of whom had untreated early PD, and 18 h ealthy controls, were examined. Odor identification and discrimination data were corrected for odor detection scores. PD patients scored significantly lower on all olfactory tests. interestingly, the subgroup of de novo patie nts with early PD also showed significant olfactory disturbances compared w ith healthy subjects. Within the PD group, using multiple regression analys is, we found a significant, negative correlation between odor discriminatio n measures and disease severity. The present study is the first to describe decreased performance of PD pati ents on odor discrimination, in addition to the already well-established de ficits in odor detection and identification. Furthermore, odor discriminati on measures were related to disease severity, possibly indicating that at l east some aspects of olfactory dysfunction in PD may be secondary to ongoin g degenerative processes in PD. As significant olfactory impairments were f ound in early, de novo PD, olfactory tests may be useful in the early diagn osis of PD.