The present study showed that high-risk subjects identified by a questionnaire survey on core prodromal symptoms (dysautonomia, hyposmia, and RBD) of health checkup examinees had mild changes in motor and cognitive scales with a higher prevalence of imaging abnormalities on DaT-SPECT than normal subjects without prodromal symptoms. In addition, those high-risk subjects also had worse scores on other questionnaires about depression and daytime sleepiness, indicating that they had multiple non-motor symptoms similar to patients with LBD. The high rate of LBD-related neurological and imaging defects in the high-risk subjects confirms the utility of a questionnaire on prodromal symptoms as a method of screening individuals at high risk of developing LBD.
Regarding the relationship between functional and imaging features, we found that DaT-SPECT abnormalities were associated with motor impairment, while MIBG scintigraphy abnormalities were associated with olfactory impairment. These findings were in line with the two major pathological development patterns of PD (brain-first and body-first) proposed based on chronological changes in imaging biomarkers.14 In the present study, the presence of DaT-SPECT abnormalities and absence of MIBG abnormalities seemed to correspond to brain-first PD, wherein patients develop dopaminergic degeneration prior to myocardial sympathetic denervation. In contrast, a decreased uptake of MIBG without DaT abnormalities was likely indicative of body-first PD, wherein the disease is initiated by non-motor features, such as myocardial sympathetic denervation, olfactory dysfunction, or RBD.15 In addition, the high-risk group with both DaT and MIBG defects were characterized by an old age and motor, cognitive, and olfactory impairment, suggesting that LBD-related pathological changes developed more extensively in such subjects and possibly closer to the onset of LBD than in other groups. Taken together, our results appear to support the different patterns of pathological development during a prodromal phase of LBD.
In the present study, the high-risk subjects with normal DaT and MIBG findings still had more minor motor and cognitive impairment and milder reductions in DaT-SPECT SBR values, albeit still within the normal range, than low-risk subjects. This result suggests that the presence of prodromal symptoms without overt imaging defects is still associated with early pathological changes of LBD. Given that these high-risk subjects’ ages were about three years younger than the groups with defects in either DaT-SPECT or MIBG scintigraphy, a longitudinal study is needed to determine if imaging abnormalities of DaT or MIBG appear within the next few years in high-risk subjects with normal imaging. We are currently performing a prospective longitudinal study, the results of which are expected to provide insight into the progression of LBD at a very early stage.
In our study, both the high-risk and low-risk subjects were identified through a questionnaire survey linked to a health checkup. This enabled us to investigate the changes in anthropometric and blood markers in the high-risk subjects of our cohort. Our results demonstrated that female high-risk subjects had decreased hematocrit with normal hemoglobin values compared with female subjects without prodromal symptoms, a pattern indicating a mild iron defect. Although not significant, similar findings were shown for the male high-risk subjects in the present study. These results were in line with literature indicating iron deficiency anemia as associated with a risk of PD onset16 but were not identical to our previous finding that male (but not female) subjects at risk of LBD had decreased hematocrit values.13 The discrepancy between the previous and present studies may stem from the size and age of the population examined, but further studies will be necessary to clarify the systemic changes in the prodromal stage of LBD.
The present study was associated with several limitations. First, this study had a small sample size of high-risk and low-risk subjects, and the data were limited to Asians. We therefore plan to increase the number of institutes in our cohort study to expand the sample size. Second, in the present study, RBD was assessed only with the RBDSQ questionnaire and not with polysomnography. Although a previous study showed that RBD can be diagnosed with an RBDSQ cut-off value of 5, as was used in our study, with a sensitivity of 88.5% and specificity of 96.9% in Japanese subjects,17 it is necessary to confirm the findings of REM sleep without atonia on polysomnography to make a definitive diagnosis of RBD. Third, only the baseline findings were available in the present study, and it is important to determine the natural history of neurological imaging indices as well as the incidence of LBD conversion in these high-risk individuals through further longitudinal analyses, which are now underway.
In summary, our study demonstrates that high-risk subjects for LBD identified in a questionnaire survey on prodromal symptoms had low SBR of DaT-SPECT. A decreased uptake in DaT-SPECT was associated with motor impairment, and a reduced MIBG uptake was associated with olfactory dysfunction. A longitudinal evaluation of both the high-risk and low-risk groups is warranted to determine the natural history of prodromal LBD.