Olfaction in Parkinson's disease.

It has become increasingly apparent that Parkinson's disease (PD) can no longer be considered purely a motor disease, as numerous sensory alterations accompany this disorder either before or early in its clinical progression. Most notable among such disturbances are decrements in smell function. Such anomalies have been documented in approximately 90% of patients with early-stage sporadic PD and appear to progress little, if at all, with the development of the more classic PD-related motor symptoms. In this paper, I briefly review the nature of the olfactory dysfunction observed in PD and current theories as to its pathological basis.