OLFACTORY TESTING DIFFERENTIATES BETWEEN PROGRESSIVE SUPRANUCLEAR PALSY AND IDIOPATHIC PARKINSONS-DISEASE

Olfactory dysfunction occurs in most patients with idiopathic Parkinso n's disease (PD). In this study, we sought to determine whether such d ysfunction is also present in progressive supranuclear palsy (PSP), a condition which shares a number of motor symptoms with PD and is commo nly misdiagnosed as PD. We administered the University of Pennsylvania Smell Identification Test, a standardized test of odor identification ability, to 21 PSP patients; 17 also received a forced-choice odor de tection threshold test. We compared the olfactory test scores to those obtained from PD patients and normal controls matched to the PSP pati ents on the basis of age, sex, and smoking habits. Overall, the olfact ory function of the PSP patients was markedly superior to that of the PD patients and did not differ significantly from that of the normal c ontrols. There was no association in either the PSP or PD patient grou ps between (1) the olfactory test scores and (2) measures of motor sym ptom severity, disease stage, and medication usage. These findings dem onstrate that patients with PSP and PD differ markedly in their abilit y to smell and suggest that olfactory testing may be useful in their d ifferential diagnosis.