Striatal dopamine transporter degeneration in right-handed REM sleep behavior disorder patients progresses faster in the left hemisphere.

OBJECTIVE

In right-handed patients with idiopathic rapid eye movement sleep behavior disorder (IRBD) or Parkinson's disease (PD), dopamine transporter (DAT) single-photon emission computed tomography (SPECT) shows a predominant nigrostriatal deficit in the left striatum. To confirm this hypothesis, we longitudinally investigated whether the nigrostriatal function is asymmetric in Japanese patients with IRBD.

METHODS

In 91 polysomnography-confirmed IRBD patients, which included 87 right-handed IRBD patients who underwent 33 repeat DAT-SPECT scans, we retrospectively examined the striatal dopaminergic terminals in each hemisphere using DAT-SPECT. We calculated the values of interhemispheric laterality index for the right and left sides.

RESULTS

The proportion of IRBD patients with lower SBR in the striatum was different between the left (n = 60, 69.0%) and right (n = 27, 31.0%) hemispheres. In the repeat DAT-SPECT scan (n = 33), the rate of decline in the striatum was greater on the left than on the right side, and the proportion of patients with lower decline rates in the left striatum (n = 25, 73.5%) was greater than the that in the right striatum (n = 3, 8.8%). The proportion of lower SBR side at baseline did not predict the development of PD or DLB.

CONCLUSION

Right-handed IRBD patients have asymmetric nigrostriatal dopaminergic function, as evidenced by the faster estimated rate of decline for the left striatum than the right striatum. The left-right hemispheric striatal predominance of the nigrostriatal deficit in the right-handed prodromal PD or DLB patients represents a difference in the early pathological process of the disease.