Olfactory bulb in multiple system atrophy.

Olfactory dysfunction is a characteristic clinical sign in Parkinson's disease (PD); it is also present in multiple system atrophy (MSA). The pathological basis of hyposmia or anosmia in PD is well known: the olfactory bulb (OB) contains numerous Lewy bodies and severe neuronal loss is present in the anterior olfactory nucleus (AON). We established that glial cytoplasmic inclusions (GCIs) are present in all the OBs from MSA cases. Their presence in the OB is diagnostic for MSA. Additionally, neuronal loss is present in the AON in MSA. These pathological changes might be responsible for the olfactory dysfunction seen in MSA.