medwireNews: Mixed fiber neuropathy (MFN) is the most common subtype of diabetic polyneuropathy (DPN) affecting people with type 1 diabetes, Danish researchers report.
The findings are in line with previous studies indicating that “DPN predominantly manifests as MFN, with affected individuals exhibiting symptoms related to both small and large nerve fibers,” write Pall Karlsson (Aarhus University) and co-authors in BMJ Open Diabetes Research & Care.
However, they point out that these studies were based on people with type 2 diabetes, and it was therefore unclear whether type 1 diabetes-associated DPN mirrors the clinical manifestations observed in type 2 diabetes.
The current study included 67 individuals with type 1 diabetes and non-painful DPN, 50 with painful DPN, and 48 with no DPN, as well as 51 healthy controls without diabetes or DPN. All participants with diabetes were aged 30–75 years and had a diabetes duration of at least 5 years.
Karlsson and colleagues developed three different models to investigate the optimal combination of DPN diagnostic tests to identify the most prevalent DPN subtype of DPN based on the type of nerve fibers affected.
Small fiber involvement was determined using intra-epidermal nerve fiber density analysis, electrochemical skin conductance in the feet, pinprick, and temperature sensation tests, while large fiber involvement was determined based on the measures of biothesiometry, DPNCheck, ankle reflexes, and 10 g monofilament.
Model 1 was based on a requirement for at least one abnormal result in any of the above tests for either small fiber neuropathy (SFN) or large fiber neuropathy (LFN) with no abnormal results for the opposing subtype (ie LFN or SNF) to diagnose either subtype. MFN was defined as at least one abnormal result in the tests for both SFN and LFN.
Model 2 required at least two abnormal SFN test results with one or fewer LFN test results to diagnose SFN, and the opposite to diagnose LFN. For MFN, at least two abnormal results were needed in both the SFN and LFN tests.
In model 3, a diagnosis of DPN with more prevalent SFN required three abnormal results in the small fiber measures and two or fewer abnormal results in the large fiber measures. Conversely, a diagnosis of DPN with more prevalent LFN required at least three abnormal results in the large fiber measures and two or fewer abnormal results in the small fiber measures, while MFN was defined as three or more abnormal results in both sets of tests.
The results showed that, for all participants with DPN combined, MFN was the predominant neuropathy subtype. However, as the diagnostic models became more stringent, the proportion with MFN decreased and the prevalence both SFN and LFN increased.
More specifically, MFN prevalence was 91.5% for all patients with DPN using model 1, decreasing to 66.7% with model 2 and 37.6% with model 3. The corresponding rates for SFN were 3.4%, 12.8%, and 10.3%, and for LFN they were 5.1%, 11.1%, and 19.7%. Non-classifiable neuropathy (NCN) was diagnosed in the remaining participants (0.0, 9.4 and 32.5%, respectively).
There were no significant differences in subtype prevalence between participants with painful and non-painful DPN, but the researchers note that, in model 3, NCN was the most common subtype among people with non-painful DPN, with a prevalence of 34.3% compared with 32.8% for MFN. For those with painful DPN, MFN was the most common subtype in model 3, accounting for 44.0% of cases, compared with a rate of 30.0% for NCN.
The researchers also investigated the distribution of neuropathy subtypes according to DPN severity. They found that MFN prevalence increased with DPN severity in all three models. In addition, DPN with a more prevalent SFN or LFN subtype decreased with increasing neuropathy severity in models 1 and 2. In model 3, the prevalence of SFN and LFN increased between no neuropathy and mild neuropathy, and then decreased between mild neuropathy and the more severe neuropathy subgroups.
“This might suggest that in mild/early stages of neuropathy, one fiber type (small or large) is more susceptible to damage,” Karlsson et al remark.
They conclude that their findings “identified a standardized diagnostic model that could be integrated into clinical practice for early subtyping of DPN in [type 1 diabetes].
“This could potentially influence treatment strategies and improve patient outcomes by targeting specific neuropathy subtypes.”
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