Objective: Traumatic brain injury (TBI) and REM behavioural disorder (RBD) are risk factors for Parkinson’s disease (PD). Dopaminergic abnormalities are often seen after TBI, but patients usually lack parkinsonian features. We test whether TBI, PD and RBD have distinct striatal dopamine abnormalities using dopamine transporter imaging.
Methods: 123I-ioflupane SPECT scans were used in a cross-sectional study to measure dopamine transporter (DaT) levels in moderate/severe TBI, healthy controls, early PD and RBD patients. Caudate and putamen DaT, putamen-to-caudate ratios and left-right symmetry of DaT were compared.
Results: 108 participants (43 TBI, 26 PD, 8 RBD, 31 controls) were assessed. Early PD patients scored significantly higher on the UPDRS motor subscale than other groups. TBI and PD patients had reduced DaT levels in the caudate (12.2% and 18.7% respectively) and putamen (9.0% and 42.6% respectively) compared to controls. RBD patients had reduced DaT levels in the putamen (12.8%) but not in the caudate compared to controls. PD and TBI patients showed distinct patterns of DaT reduction, with PD patients showing a lower putamen-to-caudate ratio. DaT asymmetry was greater in the PD group than other groups.
Conclusions: The results show that early PD and TBI patients have distinct patterns of striatal dopamine abnormalities. Early PD and moderate/severe TBI patients showed similar reductions in caudate DaT binding, but PD patients showed a greater reduction in putamen DaT and a lower putamen-to-caudate ratio. The results suggest that parkinsonian motor signs are absent in these TBI patients because of relatively intact putaminal dopamine levels.