Assessment of neuropathy subtypes in type 1 diabetes.

Introduction: Diabetic polyneuropathy (DPN), a common complication of diabetes, can manifest as small, large, or mixed fiber neuropathy (SFN, LFN, and MFN, respectively), depending on the type of fibers involved. Despite evidence indicating small fiber involvement prior to large fiber involvement in type 1 diabetes mellitus (T1DM)-associated DPN, no evidence has been produced to determine the more prevalent subtype. We aim to determine the more prevalent type of nerve fiber damage-SFN, LFN, and MFN-in T1DM-associated DPN, both with and without pain.

Research design and methods: In this cross-sectional study, participants (n=216) were divided into controls; T1DM; T1DM with non-painful DPN (NP-DPN); and T1DM with painful DPN (P-DPN). DPN was further subgrouped based on neuropathy severity. The more prevalent type of fiber damage was determined applying small and large fiber-specific tests and three diagnostic models: model 1 (≥1 abnormal test); model 2 (≥2 abnormal tests); and model 3 (≥3 abnormal tests).

Results: MFN showed the highest prevalence in T1DM-associated DPN. No differences in neuropathy subtype were found between NP-DPN and P-DPN. DPN, with prevalent SFN plateaus between models 2 and 3. All models showed increased prevalence of MFN according to DPN severity. Model 3 showed increased DPN with prevalent LFN in early neuropathy. DPN with prevalent SFN demonstrated a similar, but non-significant pattern.

Conclusions: DPN primarily manifests as MFN in T1DM, with no differentiation between NP-DPN and P-DPN. Additionally, we propose model 2 as an initial criterion for diagnosing DPN with a more prevalent SFN subtype in T1DM. Lastly, the study suggests that in mild stages of DPN, one type of nerve fiber (either small or large) is more susceptible to damage.