The course of olfactory deficits in patients with Parkinson's disease--a study based on psychophysical and electrophysiological measures.

OBJECTIVES

Patients with Parkinson's disease (PD) commonly show olfactory deficits in the early stages of the disease. These deficits can be verified psychophysically or electrophysiologically using olfactory event-related potentials (OERP). While psychophysical olfactory function in PD patients can improve over time, the course of OERPs in PD has not yet been investigated.

METHODS

Olfactory function was investigated twice in 19 patients at 5-year intervals. Psychophysical tests included the "Sniffin' Sticks" test battery. In addition, OERPs were recorded in response to two odors on each side (phenyl-ethyl-alcohol: 40% (v/v), H(2)S, 6ppm). OERPs were evaluated regarding existence (yes/no). Average disease duration at follow-up was 9.0 years and the average Hoehn and Yahr score (disease stage) was 2.2.

RESULTS

Psychophysically, 1 patient was normosmic, 14 were hyposmic, and 4 were functionally anosmic at the initial visit. Re-examination revealed 1 normosmic, 9 hyposmic, and 8 functionally anosmic patients. Mean olfactory function decreased significantly in all patients. OERPs were initially existent in 3 out of 19 patients. At follow-up, OERPs were no longer present in these patients, but were detectable in 3 other patients.

CONCLUSIONS

Overall, mean olfactory function decreased, although improvements were observed at the individual level. We confirmed previous findings regarding psychophysical follow-up results. Electrophysiological measures showed a pattern of fluctuation in olfactory function comparable to that of the psychophysical results. These fluctuations do not seem to predict the course of the disease.