Traumatic brain injury preceding clinically diagnosed α-synucleinopathies: A case-control study

ObjectiveTo determine the association between traumatic brain injury (TBI) and any clinically diagnosed alpha -synucleinopathy including Parkinson disease (PD), dementia with Lewy bodies (DLB), PD dementia (PDD), and multiple system atrophy (MSA).MethodsUsing the medical records-linkage system of the Rochester Epidemiology Project, we identified incident cases of alpha -synucleinopathies in Olmsted County, Minnesota, from 1991 to 2010, matching by age (1 year) at symptom onset and sex to controls. We reviewed records of cases and controls to detect TBI prior to clinical-motor onset of any alpha -synucleinopathies. We based severity (possible, probable, and definite) upon the Mayo Classification System for TBI Severity. Using conditional-logistic regression, we calculated the odds ratio (OR) of all alpha -synucleinopathies and type, adjusting for coffee intake and smoking.ResultsTBI frequency was lower among cases (7.0%) than controls (8.2%). No association was found between TBI and all alpha -synucleinopathies in multivariable analyses (OR 0.90, 95% confidence interval [CI] 0.54-1.52). No association presented when examining the number of TBIs, TBI severity, time between TBI exposure and index date, age at index date, or sex. When stratifying by each individual alpha -synucleinopathy, we did not identify any associations between TBI and PD, DLB, or PDD. Among the MSA group, 1 (6.4%) and 0 controls experienced a TBI (OR could not be estimated).ConclusionsIn this nested case-control population-based analysis, TBI was not associated with subsequent alpha -synucleinopathies in general or any individual alpha -synucleinopathy. This did not change based on the temporality or the severity of the TBI. Our findings may be limited by the study power.