Olfactory disturbances in Parkinson’s disease

Abstract Studies in Parkinson's disease (PD) reported an increased number of dopaminergic neurons within the olfactory bulb (OB), possibly resulting in a deficiency of the olfactory processing. It is hypothesized that such an increase in periglomerular neurons could elicit a massive inhibition of mitral cells in particular. Furthermore, the association of the substantia nigra pars compacta (SNpc) with PD olfactory disturbance has been demonstrated according to the description of a direct pathway from the SNpc to the OB. In addition, deficits of other neurotransmitter systems such as serotonergic, noradrenergic, and cholinergic projections to the OB are potentially associated with olfactory dysfunctions in PD. Moreover, the pronounced olfactory deficits in PD are associated with a higher risk for developing dementia, which strengthens the use of odor tests as possible early diagnostic methods. In addition, nonsteroidal antiinflammatory drugs potentially improve olfaction; hence, they may constitute potential candidates for the treatment of olfactory disorders in PD.