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Personality profile and its association with conversion to neurodegenerative disorders in idiopathic REM sleep behavior disorder


Cross-sectional case-control study

Demographics and personality traits of all subjects at baseline

A total of 185 patients with iRBD and 91 controls were recruited at baseline (Fig. 1: flowchart of the study). Demographic characteristics and personality traits of all subjects were shown in Table 1. The baseline age and sex were comparable between iRBD patients and controls (median [interquartile range, IQR] of age: 64.0 [12.0] vs. 66.0 [13.0] years, Z score = −0.74, p = 0.46, r = 0.045; male sex: 70.3% vs. 65.9%, χ2 = 0.54, p = 0.47, ϕ = 0.044). Although iRBD patients had a marginally higher level of education (20.0% vs. 10.2%, χ2 = 4.1, p = 0.044, Padjusted = 0.087, ϕ = 0.12), they had a relatively lower score of education-adjusted Hong Kong Montreal Cognitive Assessment (HK-MoCA) than controls (median [IQR]: 25.0 [3.0] vs. 26.0 [3.0], Z score = −2.6, p = 0.011, Padjusted = 0.037, r = 0.15). The total scores of the short form of the Beck Depression Inventory (BDI-13) (median [IQR]: 5.0 [8.0] vs. 3.0 [7.0], Z score = −3.7, p < 0.001, Padjusted = 0.002, r = 0.23) and RBD Questionnaire-Hong Kong (RBDQ-HK) (median [IQR]: 43.0 [24.0] vs. 5.0 [10.0], Z score = −12.9, p < 0.001, Padjusted < 0.001, r = 0.78) were higher in iRBD patients when compared with controls. In addition, iRBD patients had a higher percentage of current smokers (15.3% vs. 4.5%, χ2 = 6.7, p = 0.009, Padjusted = 0.036, ϕ = 0.16), marginally lower percentages of non-smokers (74.9% vs. 85.4%, χ2 = 3.9, p = 0.048, Padjusted = 0.087, ϕ = −0.12) and non-alcohol drinkers (53.0% vs. 65.9%, χ2 = 4.0, p = 0.045, Padjusted = 0.087, ϕ = −0.12), and marginally higher percentage of lifetime or current psychiatric disorders than controls (39.5% vs. 26.4%, χ2 = 4.6, p = 0.032, Padjusted = 0.083, ϕ = 0.13) (Table 1).

Fig. 1: Flowchart of study.
figure 1

DLB, Dementia with Lewy bodies; iRBD, idiopathic rapid eye movement sleep behavior disorder; MCI, mild cognitive impairment; MSA, multiple system atrophy; PD, Parkinson’s disease.

Table 1 Demographic characteristics, clinical features, and personality traits of iRBD patients and controls at baseline.

When compared with controls, iRBD patients had a higher score in neuroticism (median [IQR]: 21.0 [10.0] vs. 17.0 [10.0], Z score = −3.2, p = 0.001, Padjusted = 0.007, r = 0.19), a lower score of extraversion (mean ± standard deviation (SD): 23.2 ± 5.8 vs. 25.3 ± 5.7, t value = 2.8, degree of freedom (df) = 274, p = 0.006, Padjusted = 0.03, Hedge’s g = 0.36), and a marginally lower score of conscientiousness (median [IQR]: 31.0 [6.0] vs. 32.0 [6.6], Z score = −2.1, p = 0.033, Padjusted = 0.083, r = 0.13). The scores of openness and agreeableness were comparable between iRBD patients and controls (Table 1).

Correlations between iRBD and personality traits

iRBD was positively correlated with the score in neuroticism (β = 0.20; t = 3.3, B, 0.42; 95% CI, 0.17 to 0.66; p = 0.001; Padjusted = 0.01; post hoc power = 0.91) and negatively correlated with the score in extraversion (β = −0.17; t = 2.8; B, −0.35; 95% CI, −0.60 to −0.10; p = 0.006; Padjusted = 0.03; post hoc power = 0.79) in the unadjusted model. In addition, iRBD was marginally negatively correlated with the score in conscientiousness (β = −0.13; t = −2.2; B, −0.28; 95% CI, −0.53 to −0.03; p = 0.031; Padjusted = 0.10; post hoc power = 0.58). There was no significant correlation between iRBD and other two personality traits in the unadjusted model. In the adjusted model, iRBD was only marginally negatively correlated with the score of extraversion (β = −0.13; t = −2.0; B, −0.28; 95% CI, −0.55 to -0.001; p = 0.049; Padjusted = 0.12; post hoc power = 0.50). There was no significant correlation of iRBD with other four personality traits in the adjusted models (Table 2).

Table 2 Correlations between iRBD and personality traits.

Follow-up study

A total of 171 patients were successfully followed up with a median of 5.9 years. Among them, 47 iRBD patients (27.5%) developed neurodegenerative disorders (convertors), including 21 PD, 19 probable DLB, 4 MSA, and 3 mild cognitive impairment (MCI) (Table 3).

Table 3 Demographics, neurodegenerative biomarkers, and personality traits between non-convertors and convertors at baseline.

Table 3 shows the baseline clinical features and personality traits of iRBD patients. Convertors were older at baseline (mean ± SD: 69.6 ± 6.8 vs. 62.4 ± 9.9 years, t value = 4.6, df = 169, p < 0.001, Padjusted < 0.001, Hedge’s g = 0.79), had later onset age of RBD symptoms (median [IQR]: 61.5 [9.0] vs. 58.0 [11.0] years, Z score = −3.0, p = 0.003, Padjusted = 0.02, r = 0.23), and had a shorter follow-up duration (median [IQR]: 4.9 [5.5] vs. 6.3 [4.5] years, Z score = −3.3, p = 0.001, Padjusted = 0.009, r = 0.25) compared with non-convertors (neurodegenerative disease-free patients during follow-up). Convertors had a marginally higher percentage of former smokers (17.8% vs. 7.3%, χ2 = 4.0, p = 0.044, Padjusted = 0.14, ϕ = 0.16), but a marginally lower percentage of current alcohol drinkers (22.2% vs. 40.2%, χ2 = 4.6, p = 0.031, Padjusted = 0.13, ϕ = −0.17) and current smokers (6.7% vs. 20.2%, χ2 = 4.4, p = 0.037, Padjusted = 0.14, ϕ = −0.16) when compared with non-convertors. In addition, Convertors had a lower percentage of comorbidity of psychiatric disorders than non-convertors (17.0% vs. 47.6%, χ2 = 13.4, p < 0.001, Padjusted = 0.003, ϕ = −0.28). There was a marginally lower score of olfactory identification test in convertors as compared with non-convertors (1.0 [2.0] vs. 2.0 [3.0], Z score = −2.2, p = 0.026, Padjusted = 0.13, ϕ = 0.18). There was no statistically significant difference in sex, duration of RBD, education level, phasic and tonic electromyography (EMG) level, scores of the RBDQ-HK, BDI-13, Epworth Sleepiness Scale, Unified Parkinson’s Disease Rating Scale-part III, education-adjusted HK-MoCA, and personality traits between the two groups.

Correlations of personality traits with conversion risk in iRBD patients

In the unadjusted Cox regression model, openness was a marginally significant predictor of conversion (hazard ratio (HR) = 0.73; 95% CI = 0.54 to 0.98; p = 0.035; Padjusted = 0.12; post hoc power = 0.54). In the adjusted Cox regression models, both neuroticism and extraversion were statistically significant predictors of conversion. An increase of one SD score from mean in neuroticism was associated with an 100% increased risk of conversion (adjusted HR, 2.0; 95% CI, 1.3 to 3.1; p = 0.002; Padjusted = 0.01; post hoc power = 0.86), while an increase of one SD score from mean in extraversion was associated with a 47% decreased risk (adjusted HR, 0.53; 95% CI, 0.36 to 0.77; p < 0.001; Padjusted = 0.009; post hoc power = 0.79) (Table 4).

Table 4 Risk of neurodegenerative disorders by personality traits in iRBD patients.



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