Detrimental effect of type 2 diabetes mellitus in a large case series of Parkinson's disease

Introduction: To investigate the effect of diabetes mellitus (DM) on the clinicoradiological features in patients with Parkinson's disease (PD). Methods: 671 patients with de novo PD were classified into two groups according to the presence of DM (106 with DM and 565 without). We performed inter-group comparative analyses of the striatal dopamine transporter (DAT) availability in all patients and level of cognitive performances in 312 patients (58 with DM and 254 without). Neuroimaging analyses of cortical thickness were performed in 42 patients with DM and 42 matched patients without DM. We assessed the longitudinal changes in the levodopa-equivalent dose (LED) across time in 549 patients who were treated for at least two years (86 with DM and 463 without) using a linear mixed model. Results: The PD patients with DM were older at the onset of parkinsonism and had more severely decreased baseline DAT availability in the caudate and ventral striatum than those without DM. The PD group with DM showed poorer performances in attention/working memory and frontal/executive function than the group without DM. Cortical thinning in the right inferomedial temporal lobe was observed in PD with DM group relative to PD without DM group. During follow-up, the PD patients with DM showed a more rapid longitudinal increase in LED than those without DM. Conclusion: Our results suggest that coexistent DM may have a detrimental effect on disease progression as well as baseline striatal dopamine loss, brain structural alterations, and cognitive performances in patients with PD.