Demographic characteristics
The demographic data of the two groups are shown in Table 1. There were 250 patients in the MSD group (168 males and 82 females) and 64 patients in the non-MSD group (40 males and 24 females). The average age was 64.3 ± 9.5 years in the MSD group and 62.3 ± 8.7 years in the non-MSD group. Student’s t-test analysis showed that there was no significant difference in the average age, age at PD onset, and duration of PD between the two groups (all P >0.05). The proportion of patients with a family history of PD was similar in both groups (P >0.05).
The Chi-squared test revealed that a higher percentage of patients engaged in manual labor in the MSD group (68.00%) than in the non-MSD group (53.13%; P = 0.026). More patients in the MSD group (84.00%) had a low level of education (lack of post-secondary education in university) than patients in the non-MSD group (59.37%; P <0.001). A higher percentage of patients were bilingual speakers in the MSD group (20.40%) than in the non-MSD group (9.38%; P=0.041). More patients in the MSD group (70.40%) had a low income (lower than 5500 yuan) compared to those in the non-MSD group (56.25%; P=0.031). However, there were no significant differences between these two groups in terms of gender, marital status, or leisure activities (P > 0.05 for all).
Clinical characteristics
Data on the clinical characteristics of the two groups are shown in Table 2. There were no significant differences between the two groups in terms of hypertension, hyperlipidemia, ischemic heart disease, or diabetes mellitus (P >0.05 for all).
The Chi-squared test revealed that there were higher incidence of frontal lobe lesions in the MSD group (78.00%) than in the non-MSD group (59.38%; P=0.002). Similarly, there were higher incidence of temporal lobe lesions in the MSD group (51.60%) than in the non-MSD group (35.94%; P =0.025). In addition, a higher percentage of patients had concurrent dysphagia in the MSD group (46.40%) than in the non-MSD group (31.25%; P = 0.029). However, no significant differences were found in terms of parietal lobe lesion, occipital lobe lesions, concurrence with other CNS diseases and tremor dominant forms between these two groups (P>0.05 for all).
Anti-PD drugs, such as Levodopa, selegiline, and amantadine, were prescribed more often in the MSD group, while dopamine agonists were prescribed more often in the non-MSD group. However, there were no significant differences in the medication frequency or Levodopa equivalent dose between the two groups (P >0.05 for all).
PD-associated evaluations
The differences in the PD-associated evaluations between the two groups are shown in Table 3. The Mann-Whitney U test revealed that the ADL score was lower in the MSD group than in the non-MSD group (P = 0.020). However, there was no significant difference in the Hoehn & Yahr stage score and duration of PD between the MSD group and non-MSD group (P = 0.095).
Regarding the UPDRS score, the MDS-UPDRS part III, UPDRS tremor score, and UPDRS PIGD scores were numerically, but not significantly, higher in the MSD group compared to the non-MSD group after the Mann-Whitney U test (P > 0.05 for all).
In the univariate analysis of the NMSS scores, the Mann-Whitney U test revealed that both NMSS domain 4 (perceptual problem) and NMSS domain 5 (attention/memory) scores were significantly higher in the MSD group than in the non-MSD group (P = 0.033 and P < 0.001, respectively). However, there were no significant differences in the other NMSS domain scores between the two groups (P > 0.05 for all).
Multivariate logistic regression
At first, 10 significant factors resulted from the t-tests, Mann-Whitney U tests and Chi-squared tests, including educational level, occupation, monthly income, speaking background, frontal lobe lesions, temporal lobe lesions, concurrent dysphagia, ADL score, NMSS domain 4 score (perceptual problems) and NMSS domain 5 score (attention/memory) were included for multivariate logistic regression analysis. To reduce the potential FWER attributable to t-tests and Mann-Whitney U tests, a Bonferroni correction of P-value (0.05/10=0.005) was reviewed to be a statistical significance. After the multivariate logistic regression analysis, 7 factors were excluded from the pool of independent risk factors. On the other hand, potential risk factors, including educational level, frontal lobe lesions, and NMSS domain 5 score (attention/memory), had a significant power to predict risk for MSD in PD (see Table 4).
The patients with a higher educational level [OR = 0.674, 95% CI (0.590, 0.808)] had a lower likelihood of PD-associated MSD. However, patients with a higher occurrence of frontal lobe lesions [OR = 5.145, 95% CI (2.018, 7.308)], or higher NMSS domain 5 scores (attention/memory) [OR = 10.458, 95% CI (6.164, 15.209)] had a higher likelihood of PD-associated MSD.