The Relationship between Polyneuropathy and Cognitive Functions in Type 2 Diabetes Mellitus Patients

Type 2 Diabetes Mellitus (DM) is a risk factor for mild cognitive impairment (MCI), Alzheimer's disease and vascular dementia. However, it is not known which pathophysiological mechanisms lead to impairment in cognitive functions in Type 2 DM. This study aims to compare the cognitive functions of diabetic patients with and without polyneuropathy using standardized Mini-Mental Test (MMSE) and the Montreal Cognitive Assessment Scale (MoCA) and to assess whether the presence of polyneuropathy is a predictive factor for the development of cognitive impairment.

Patients with DM who underwent our EMG laboratory for polyneuropathy between January 2014 and January 2015 were included in this study. Patients who underwent electrophysiological examinations were evaluated for polyneuropathy. Patients with polyneuropathy were classified as a patient group and other patients as a control group. In all cases, MMSE and MoCA were administered. The demographic data and educational status of the patients were recorded. Hypertension, coronary artery disease, smoking and alcohol use were questioned. Their complaints, duration of illness and the treatment they were receiving were questioned. Glycosylated hemoglobin (HBA1C) values in the last three months and physical examination findings of patients were recorded. Patients with and without polyneuropathy were compared with statistical methods.

Polyneuropathy was detected in 34 (42%) of the 81 patients who participated in our study. The age, disease duration and HBA1C levels were statistically higher in the polyneuropathy group than in the control group (p=0.024, p=0.000, p=0.016). However, there was no statistically significant difference between MMSE and MoCA scores of these groups. In both groups, there were no patients scoring below the MMSE cut-off value of 24. Seventeen of the 34 patients (50%) in the polyneuropathic group and 19 (40,4%) of the 47 patients in the control group had scores below the MoCA cut-off value 21. However, there was no statistically significant difference between the two groups. We also found that the mean MoCA value of all DM patients was 21, which was the MoCA cut-off value. Also, factors affecting cognitive functions in all Type 2 DM patients were evaluated by logistic regression analysis, and it was found that duration of education was an independent factor affecting cognitive impairment (OR=8.167; p=0.001).

In our study, we did not observe significant differences between MMSE and MoCA scores of Type 2 DM patients with and without polyneuropathy. However, the cross-sectional nature of our study makes it impossible to comment on this issue. To clarify whether the presence of polyneuropathy is a predictive factor in the development of cognitive impairment in Type 2 DM, there is a need for a larger sample group and long-term follow-up studies. It has also been shown that patients with Type 2 DM may have low scores according to the MOBID cut-off value even though peripheral neurologic involvement findings are not observed. In the Type 2 DM population, it has also been shown that MoCA may be affected by education level.