It has been proposed that alpha-synuclein (αSyn) pathology in Parkinson's disease (PD) spreads in a predictable caudo-rostral way with the earliest changes seen in the dorsal motor nucleus of the vagus nerve (DMV). However, the reliability of this stereotypical spread of αSyn pathology has been questioned. In addition, the comparative occurrence of αSyn pathology in the spinal cord and brain has not been closely studied.Methods
In order to address these issues, we have examined 71 cases of PD from the UK Parkinson's Disease Society Tissue Bank at Imperial College, London. The incidence and topographic distribution of αSyn pathology in several brain regions and the spinal cord were assessed.Results
The most affected regions were the substantia nigra (SN; in 100% of cases) followed by the Nucleus Basalis of Meynert (NBM) in 98.5%. Fifty-three per cent of cases showed a distribution pattern of αSyn compatible with a caudo-rostral spread of αSyn through the PD brain. However, 47% of the cases did not fit the predicted spread of αSyn pathology and in 7% the DMV was not affected even though αSyn inclusions were found in SN and cortical regions. We also observed a high incidence of αSyn in the spinal cord with concomitant affection of the DMV and in a few cases in the absence of DMV involvement.Conclusions
Our results demonstrate a predominant involvement of the SN and NBM in PD but do not support the existence of a medullary induction site of αSyn pathology in all PD brains.