Open Access research article:
Multiple system atrophy pathology is associated with primary Sjögren's syndrome
pubmed.ncbi.nlm.nih.gov/326...
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Among possible relationships to consider is the possibility of a common risk factor such as solvent exposure.
Another possible connection - loss of saliva in Sjogrens can lead to low B12; low B12 levels are associated with shorter survival time from diagnosis in MSA.