Declining Incidence Rates of Distal Symmetric Polyneuropathy in People With Type 1 and Type 2 Diabetes in Denmark, With Indications of Distinct Patterns in Type 1 Diabetes

<bold>Objective: </bold>It is not known if incidence rates for diabetic distal symmetric polyneuropathy (DSPN) are decreasing, as they are for other diabetic complications. Here, we investigated incidence rates of DSPN in type 1 and type 2 diabetes in a large population-based study. <bold>Research design and methods: </bold>In the period 1996 to 2018, 19,342 individuals were identified at a Danish tertiary diabetes center. Vibration perception threshold was assessed by biothesiometry and repeated throughout the study. Exclusion of prevalent DSPN cases or missing data left data on 9,473 individuals for analysis of DSPN using a cutoff of >25 V and on 2,783 individuals for analysis using an age-, sex-, and height-specific cutoff. Poisson regression analysis was used to model incidence rates of DSPN for both cutoff types and separately for diabetes types. Covariates were sex, age, diabetes duration, and calendar time. <bold>Results: </bold>Incidence rates (95% CI) of DSPN decreased from 1996 to 2018 (e.g., from 4.78 [3.60-6.33]/100 person-years [PY] to 1.15 [0.91-1.47]/100 PY for 40-year-old men with type 1 diabetes and from 16.54 [11.80-23.18]/100 PY to 8.02 [6.63-9.69]/100 PY for 60-year-old men with type 2 diabetes, when using >25 V as the cutoff value). Analyses using age-, sex-, and height-specific cutoff values demonstrated similar incidence patterns by calendar time without sex differences. For type 1 diabetes, decreasing incidence rates were seen with older age. <bold>Conclusions: </bold>Incidence rates for DSPN are declining in type 1 and type 2 diabetes, possibly due to improved diabetes treatment. This causality remains to be explored. Distinct age-related patterns indicate that the pathophysiology of DSPN may differ between diabetes types.