Objective: In this study, we aim to investigate whether Type 2 diabetes (T2DM) influences the phenotype of Parkinson’s disease (PD).

Background: In PD, T2DM may serve as both a risk factor and a determinant of disease progression. Some studies suggest that concurrent T2DM could lead to accelerated motor and cognitive decline in PD patients compared to those without T2DM. There is evidence not only of common biological mechanisms and genetic links between these diseases but also that T2DM may contribute to neurodegeneration through indirect mechanisms such as chronic systemic inflammation and hyperglycemia.

Method: For this study, demographic and clinical data from 247 PD patients who were drug-naïve states were collected. We defined individuals who are taking diabetes medications or have a hemoglobin A1c (HbA1c) level of 6.5% or higher as the PD with DM group, those with an HbA1c level ranging from 5.7% to 6.4% as the PD with prediabetes group, and those with an HbA1c level below 5.7% as the PD without DM group. A motor asymmetry index (AI) was calculated as the absolute value of the difference between the right and left scores from the UPDRS-III score. In other words, a higher AI indicates greater asymmetry, while a lower AI indicates a more symmetric motor symptom.

Results: A total of 57 patients of PD with DM, 74 patients of PD with prediabetes, and 135 patients of PD without DM were enrolled. The PD with DM group had an average age that was 4 years older compared to the other two groups, but there were no differences in gender composition and disease duration among the three groups. Although there were no statistically significant differences, the PD with DM group tended to show higher UPDRS scores and poorer cognition compared to the other two groups. The PD with DM group exhibited lower AI values compared to the other two groups (0.19 vs 0.30 vs 0.29, p = 0.021). In addition, PD with DM group revealed significantly higher two inflammatory indexes (neutrophil to high-density lipoprotein cholesterol [HDL] ratio and monocyte to HDL ratio levels) compared to the other two groups (p = 0.002 and p = 0.007, respectively).

Conclusion: Our study indicates that T2DM may influence the phenotype of PD, as evidenced by poorer cognition, lower motor asymmetry, and elevated inflammatory indexes compared to those without diabetes or prediabetes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effect-of-diabetes-mellitus-on-the-phenotype-of-parkinsons-disease/