Diabetic polyneuropathy: Progress in diagnostic strategy and novel target discovery, but stagnation in drug development

Polyneuropathy in Parkinson's Disease is Highly Prevalent and Not Related to Treatment

PURPOSE

An increased prevalence of peripheral polyneuropathy (PN) in Parkinson's disease (PD) associated with greater functional impairment has previously been reported. A possible cause has been suggested as levodopa therapy. The aim of this real-world study was to assess the prevalence and the characteristics of PN in PD and to investigate the putative association between PN and oral levodopa.

METHODS

A cohort of 692 consecutive patients with idiopathic PD had routine clinical, laboratory, and lower limb clinical neurophysiology assessment when attending the certified tertiary Parkinson center, Schön Klinik Neustadt, Neustadt in Holstein, Germany, between 2016 and 2019. Patients were sent by general neurologists for the medication adjustment, physiotherapy, ergotherapy, and logopaedic treatment. A retrospective cross-sectional review of the data was performed.

FINDINGS

The mean age of the cohort was 72.6 (8.44) years (range, 44-90 years) and 60% were male. The age of the first PD manifestation was 65.22 (10.09) years (range, 31-88 years). Of 692 patients with PD, 507 (73.27%) had clinical signs of neuropathy and PN was first diagnosed 6.3 (5.7) years after the PD onset. Of these 507 patients, 446 (87.96%) underwent the electrophysiological investigations with PN confirmed in 396 patients (88.79% out of 446 electrophysiologically investigated patients with PD). Peripheral polyneuropathy was ruled out in 50 patients (11.21% of 446 electrophysiologically investigated patients with PD). The half of patients had moderate and severe sensory axonal PN (201 patients or 53.03% of all 396 with confirmed PN). The mean motor examination part of the Movement Disorders Society's Unified PD Rating Scale score in patients with PN was significantly higher (off, 30.48 [11.60] points; on, 19.92 [10.27] points), than in patients without PN (off, 27.17 [14.57] points; on, 17.14 [11.98] points), with P < 0.01 in the both off and on states. The mean levodopa daily dosage was similar in patients with PN and without PN (565 mg vs 556 mg, P = nonsignificant). No difference between other dopaminergic medication in PN and non-PN group was found.

IMPLICATIONS

PN is highly prevalent in patients with PD. There was no association between oral levodopa or other dopaminergic medication and PN. More awareness of PN in PD clinics and further understanding of the pathophysiology, which leads to the development of an axonal polyneuropathy in PD, are required.

Association of Nerve Conduction Study Variables with Hematologic Tests in Patients with Type 2 Diabetes Mellitus

Background and Objective: Diabetic peripheral neuropathy (DPN) is a prevalent complication of type 2 diabetes mellitus (T2DM), with nerve conduction studies (NCSs) serving as the diagnostic gold standard. Early diagnosis is critical for effective management, yet many cases are detected late due to the gradual onset of symptoms. This study explores the relationship between hematological tests and NCS outcomes in T2DM patients to improve the early detection of DPN. Material and Methods: This retrospective study involved T2DM patients exhibiting neuropathic symptoms, and patients were divided based on NCS findings into groups with normal and abnormal results to assess the diagnostic value of various hematological markers, clinical, and demographic data for DPN. Results: Among 400 participants, 57% (n = 228) had abnormal NCS results indicative of DPN. Significant differences were observed in the abnormal-NCS group, including older age, longer diabetes duration, higher levels of fasting plasma glucose, HbA1c, and apolipoprotein B, along with lower eGFR, HDL-C, and Apo A-I levels. Notably, negative correlations were found between HDL-C, Apo A-I, vitamin B12, and specific NCS measurements, while positive correlations existed with sural sensory nerve amplitudes. Multivariate analysis highlighted the importance of age, diabetes duration, hyperglycemia, and specific hematologic markers in predicting DPN. Conclusions: The findings confirm that NCSs, combined with hematologic testing, can effectively identify DPN in T2DM patients. Consistent with prior research, prolonged hyperglycemia and nephropathy progression are strongly linked to DPN development. Additionally, lower levels of HDL-C, Apo A-I, and vitamin B12 are associated with the condition, suggesting their potential utility in early diagnostic protocols.

Troponin T Is Negatively Associated With 3 Tesla Magnetic Resonance Peripheral Nerve Perfusion in Type 2 Diabetes

OBJECTIVE

The pathogenesis of diabetic polyneuropathy (DN) is poorly understood and given the increasing prevalence of DN, there is a need for clinical or imaging biomarkers that quantify structural and functional nerve damage. While clinical studies have found evidence of an association between elevated levels of troponin T (hsTNT) and N-terminal pro brain natriuretic peptide (proBNP) with microvascular compromise in type 2 diabetes (T2D), their implication in mirroring DN nerve perfusion changes remains unclear. The objective of this study was, therefore, to investigate whether hsTNT and proBNP assays are associated with MRI nerve perfusion in T2D.

METHODS

In this prospective cross-sectional single-center case-control study, 56 participants (44 with T2D, 12 healthy control subjects) consented to undergo magnetic resonance neurography (MRN) including dynamic contrast-enhanced (DCE) perfusion imaging of the right leg. Using the extended Tofts model, primary outcome parameters that were quantified are the sciatic nerve's microvascular permeability (K^trans), the extravascular extracellular volume fraction (v_e), and the plasma volume fraction (v_p), as well as hsTNT and proBNP values from serological workup. Further secondary outcomes were clinical, serological, and electrophysiological findings.

RESULTS

In T2D patients, hsTNT was negatively correlated with K^trans (r=-0.38; p=0.012) and v_e (r=-0.30; p=0.048) but not with v_p (r=-0.16; p=0.294). HsTNT, K^trans, and v_e were correlated with peroneal nerve conduction velocities (NCVs; r=-0.44; p=0.006, r=0.42; p=0.008, r=0.39; p=0.014), and tibial NCVs (r=-0.38;p=0.022, r=0.33; p=0.048, r=0.37; p=0.025). No such correlations were found for proBNP.

CONCLUSIONS

This study is the first to find that hsTNT is correlated with a decrease of microvascular permeability and a reduced extravascular extracellular volume fraction of nerves in patients with T2D. The results indicate that hsTNT may serve as a potential marker for the assessment of nerve perfusion in future studies on DN.