ABSTRACT
As noted in the previous chapter, the ability to smell is decreased in many, but not all, neurodegenerative diseases. Moreover, the proportion of affected individuals typically varies from disease to disease, as does the severity of the affliction. What are the reasons for such selective differences? While in the case of multiple sclerosis (MS), active plaques in olfaction-related central nervous system regions are known to correlate highly with olfactory deficits (Doty et al., 1997), such clear-cut causal associations have not been made in other neurodegenerative disorders. Furthermore, the problem is compounded by the observation that smell loss occurs early in the progression of several neurological disorders, long before rampant neuronal death or other measurable events of later-stage disease appear.
