Axonal dysfunction prior to neuropathy onset in type 1 diabetes

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

Investigating the Neuroprotective Effect of Oral Omega-3 Fatty Acid Supplementation in Type 1 Diabetes (nPROOFS1): A Randomized Placebo-Controlled Trial

This randomized, double-masked, placebo-controlled trial evaluated the effects of oral omega-3 (n-3) fatty acid supplementation on peripheral nerves in type 1 diabetes. Participants with type 1 diabetes were assigned (1:1) to n-3 (1,800 mg/day fish oil) or placebo (600 mg/day olive oil) supplements for 180 days. The primary outcome was change from baseline in central corneal nerve fiber length (CNFL) at day 180. Secondary outcomes included change in other corneal nerve parameters, corneal sensitivity, peripheral small and large nerve fiber function, and ocular surface measures. Efficacy was analyzed according to the intention-to-treat principle. Safety assessments included diabetic retinopathy grade and adverse events. Between July 2017 and September 2019, 43 participants received n-3 (n = 21) or placebo (n = 22) supplements. All participants, except for two assigned to placebo, completed the trial. At day 180, the estimated increase in CNFL in the n-3 group, compared with placebo, was 2.70 mm/mm² (95% CI 1.64, 3.75). The Omega-3 Index increased relative to placebo (3.3% [95% CI 2.4, 4.2]). There were no differences in most small or large nerve fiber functional parameters. Adverse events were similar between groups. In conclusion, we found in this randomized controlled trial that long-chain n-3 supplements impart corneal neuroregenerative effects in type 1 diabetes, indicating a role in modulating peripheral nerve health.

Novel and Emerging Electrophysiological Biomarkers of Diabetic Neuropathy and Painful Diabetic Neuropathy

PURPOSE

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes. Small and large peripheral nerve fibers can be involved in DPN. Large nerve fiber damage causes paresthesia, sensory loss, and muscle weakness, and small nerve fiber damage is associated with pain, anesthesia, foot ulcer, and autonomic symptoms. Treatments for DPN and painful DPN (pDPN) pose considerable challenges due to the lack of effective therapies. To meet these challenges, there is a major need to develop biomarkers that can reliably diagnose and monitor progression of nerve damage and, for pDPN, facilitate personalized treatment based on underlying pain mechanisms.

METHODS

This study involved a comprehensive literature review, incorporating article searches in electronic databases (Google Scholar, PubMed, and OVID) and reference lists of relevant articles with the authors' substantial expertise in DPN. This review considered seminal and novel research and summarizes emerging biomarkers of DPN and pDPN that are based on neurophysiological methods.

FINDINGS

From the evidence gathered from 145 papers, this submission describes emerging clinical neurophysiological methods with potential to act as biomarkers for the diagnosis and monitoring of DPN as well as putative future roles as predictors of response to antineuropathic pain medication in pDPN. Nerve conduction studies only detect large fiber damage and do not capture pathology or dysfunction of small fibers. Because small nerve fiber damage is prominent in DPN, additional biomarkers of small nerve fiber function are needed. Activation of peripheral nociceptor fibers using laser, heat, or targeted electrical stimuli can generate pain-related evoked potentials, which are an objective neurophysiological measure of damage along the small fiber pathways. Assessment of nerve excitability, which provides a surrogate of axonal properties, may detect alterations in function before abnormalities are detected by nerve conduction studies. Microneurography and rate-dependent depression of the Hoffmann-reflex can be used to dissect underlying pain-generating mechanisms arising from the periphery and spinal cord, respectively. Their role in informing mechanistic-based treatment of pDPN as well as facilitating clinical trials design is discussed.

IMPLICATIONS

The neurophysiological methods discussed, although currently not practical for use in busy outpatient settings, detect small fiber and early large fiber damage in DPN as well as disclosing dominant pain mechanisms in pDPN. They are suited as diagnostic and predictive biomarkers as well as end points in mechanistic clinical trials of DPN and pDPN.

Differences and Similarities in Neuropathy in Type 1 and 2 Diabetes: A Systematic Review

Background: Diabetic neuropathy is defined as the dysfunction of the peripheral nervous system in diabetic patients. It is considered a microvascular complication of diabetes mellitus. Its presence is associated with increased morbidity and mortality. Although several studies have found alterations at somatic motor, sensory levels and at the level of autonomic nervous system in diabetic patients, there is not a systematic approach regarding the differences in neuropathy between the major variants of diabetes, e.g., type 1 and 2 diabetes at both neurological and molecular level. Data sources: we systematically (Medline, Scopus, and Cochrane databases) evaluated the literature related to the difference of neuropathy in type 1 and 2 diabetes, differences in molecular biomarkers. Study characteristics: seventeen articles were selected based on pre-defined eligibility criteria. Conclusions: both superficial sensitivity (primarily thermal sensitivity to cold) and deep sensitivity (such as vibratory sensitivity), have been reported mainly in type 2 diabetes. Cardiac autonomic neuropathy is one of the diabetic complications with the greatest impact at a clinical level but is nevertheless one of the most underdiagnosed. While for type 1 diabetes patients most neuropathy alterations have been reported for the Valsalva maneuver and for the lying-to-standing test, for type 2 diabetes patients, alterations have been reported for deep-breathing test and the Valsalva test. In addition, there is a greater sympathetic than parasympathetic impairment, as indicated by the screening tests for autonomic cardiac neuropathy. Regarding subclinical inflammation markers, patients with type 2 diabetes showed higher blood levels of inflammatory markers such as high-sensitivity C-reactive protein, proinflammatory cytokines IL-6, IL-18, soluble cell adhesion molecules and E-selectin and ICAM-1, than in type 1 diabetes patients. By contrast, the blood levels of adiponectin, an adipocyte-derived protein with multiple paracrine and endocrine activities (anti-inflammatory, insulin-sensitizing and proangiogenic effects) are higher in type 1 than in type 2 diabetic patients. This review provides new insights into the clinical differences in type 1 and 2 diabetes and provide future directions in this research field.

Chronic kidney disease as a risk factor for peripheral nerve impairment in older adults: A longitudinal analysis of Health, Aging and Body Composition (Health ABC) study

Introduction

Sensory and motor nerve deficits are prevalent in older adults and are associated with loss of functional independence. We hypothesize that chronic kidney disease predisposes to worsening sensorimotor nerve function over time.

Materials and methods

Participants were from the Health, Aging and Body Composition Study (N = 1121) with longitudinal data between 2000–01 (initial visit) and 2007–08 (follow-up visit). Only participants with non-impaired nerve function at the initial visit were included. The predictor was presence of CKD (estimated GFR ≤ 60 ml/min/1.73m²) from the 1999–2000 visit. Peripheral nerve function outcomes at 7-year follow-up were 1) Motor: “new” impairments in motor parameters (nerve conduction velocity NCV < 40 m/s or peroneal compound motor action potential < 1 mv) at follow-up, and 2) Sensory: “new” impairment defined as insensitivity to standard 10-g monofilament or light 1.4-g monofilament at the great toe and “worsening” as a change from light to standard touch insensitivity over time. The association between CKD and “new” or “worsening” peripheral nerve impairment was studied using logistic regression.

Results

The study population was 45.9% male, 34.3% Black and median age 75 y. CKD participants (15.6%) were older, more hypertensive, higher in BMI and had 2.37 (95% CI 1.30–4.34) fold higher adjusted odds of developing new motor nerve impairments in NCV. CKD was associated with a 2.02 (95% CI 1.01–4.03) fold higher odds of worsening monofilament insensitivity. CKD was not associated with development of new monofilament insensitivity.

Conclusions

Pre-existing CKD leads to new and worsening sensorimotor nerve impairments over a 7-year time period in community-dwelling older adults.

Evidence of Altered Peripheral Nerve Function in a Rodent Model of Diet-Induced Prediabetes

Peripheral neuropathy (PN) is a debilitating complication of diabetes that affects >50% of patients. Recent evidence suggests that obesity and metabolic disease, which often precede diabetes diagnosis, may influence PN onset and severity. We examined this in a translationally relevant model of prediabetes induced by a cafeteria (CAF) diet in Sprague–Dawley rats (n = 15 CAF versus n = 15 control). Neuropathy phenotyping included nerve conduction, tactile sensitivity, intraepidermal nerve fiber density (IENFD) and nerve excitability testing, an in vivo measure of ion channel function and membrane potential. Metabolic phenotyping included body composition, blood glucose and lipids, plasma hormones and inflammatory cytokines. After 13 weeks diet, CAF-fed rats demonstrated prediabetes with significantly elevated fasting blood glucose, insulin and impaired glucose tolerance as well as obesity and dyslipidemia. Nerve conduction, tactile sensitivity and IENFD did not differ; however, superexcitability was significantly increased in CAF-fed rats. Mathematical modeling demonstrated this was consistent with a reduction in sodium–potassium pump current. Moreover, superexcitability correlated positively with insulin resistance and adiposity, and negatively with fasting high-density lipoprotein cholesterol. In conclusion, prediabetic rats over-consuming processed, palatable foods demonstrated altered nerve function that preceded overt PN. This work provides a relevant model for pathophysiological investigation of diabetic complications.

Altered peripheral nerve structure and function in latent autoimmune diabetes in adults

AIM

The present study was undertaken to investigate mechanisms of peripheral nerve dysfunction in latent autoimmune diabetes in adults (LADA).

MATERIALS AND METHODS

Participants with LADA (n = 15) underwent median nerve ultrasonography and nerve excitability to examine axonal structure and function, in comparison to cohorts of type 1 diabetes (n = 15), type 2 diabetes (n = 23) and healthy controls (n = 26). The LADA group was matched for diabetes duration, glycaemic control, and neuropathy severity with the type 1 and type 2 diabetes groups. A validated mathematical model of the human axon was utilized to investigate the pathophysiological basis of nerve dysfunction.

RESULTS

The most severe changes in nerve structure and function were noted in the LADA group. The LADA cohort demonstrated a significant increase in nerve cross-sectional area compared to type 1 participants and controls. Compared to type 1 and 2 diabetes, measures of threshold electrotonus, which assesses nodal and internodal conductances, were significantly worse in LADA in response to both depolarising currents and hyperpolarising currents. In the recovery cycle, participants with LADA had a significant increase in the relative refractory period. Mathematical modelling of excitability recordings indicated the basis of nerve dysfunction in LADA was different to type 1 and 2 diabetes.

CONCLUSIONS

Participants with LADA exhibited more severe changes in nerve function and different underlying pathophysiological mechanisms compared to participants with type 1 or 2 diabetes. Intensive management of risk factors to delay the progression of neuropathy in LADA may be required.

Peripheral Neuropathy as a Component of Skeletal Disease in Diabetes

PURPOSE OF REVIEW

The goal of this review is to explore clinical associations between peripheral neuropathy and diabetic bone disease and to discuss how nerve dysfunction may contribute to dysregulation of bone metabolism, reduced bone quality, and fracture risk.

RECENT FINDINGS

Diabetic neuropathy can decrease peripheral sensation (sensory neuropathy), impair motor coordination (motor neuropathy), and increase postural hypotension (autonomic neuropathy). Together, this can impair overall balance and increase the risk for falls and fractures. In addition, the peripheral nervous system has the potential to regulate bone metabolism directly through the action of local neurotransmitters on bone cells and indirectly through neuroregulation of the skeletal vascular supply. This review critically evaluates existing evidence for diabetic peripheral neuropathy as a risk factor or direct actor on bone disease. In addition, we address therapeutic and experimental considerations to guide patient care and future research evaluating the emerging relationship between diabetic neuropathy and bone health.

Measurement of axonal excitability: Consensus guidelines

Measurement of axonal excitability provides an in vivo indication of the properties of the nerve membrane and of the ion channels expressed on these axons. Axonal excitability techniques have been utilised to investigate the pathophysiological mechanisms underlying neurological diseases. This document presents guidelines derived for such studies, based on a consensus of international experts, and highlights the potential difficulties when interpreting abnormalities in diseased axons. The present manuscript provides a state-of-the-art review of the findings of axonal excitability studies and their interpretation, in addition to suggesting guidelines for the optimal performance of excitability studies.

Correlation between markers of peripheral nerve function and structure in type 1 diabetes

BACKGROUND

Clinical and experimental studies in patients with type 1 and type 2 diabetes have demonstrated changes in ion channel function and nerve structure. In this study, we investigated the relationship between axonal dysfunction and morphological change in diabetic polyneuropathy by using neuromuscular ultrasound and nerve excitability techniques. We also explored possible differences in this relationship between type 1 and type 2 diabetes.

METHODS

Nerve ultrasound and corresponding motor excitability studies were undertaken in 110 diabetes patients (50 type 1; 60 type 2) and 60 age-matched controls (30 for each group). Neuropathy severity was assessed by using total neuropathy score. Median and tibial nerve cross-sectional areas were measured at nonentrapment sites by using high-resolution linear probe.

RESULTS

Median and tibial nerve cross-sectional areas were significantly higher in diabetes patients compared with controls: type 1 (median = 7.6 ± 0.2 mm² vs 6.3 ± 0.1 mm² ; tibial = 14.5 ± 0.7 mm² vs 10.8 ± 0.3 mm² , P < .05) and type 2 (median = 9.1 ± 0.3 mm² vs 7.2 ± 0.1 mm² ; tibial = 18.5 ± 1.0 mm² vs 12.8 ± 0.5 mm² , P < .05). In the type 1 cohort, significant correlations were found between nerve cross-sectional area and excitability parameters including resting current-threshold slope (median: r = 0.523, P < .0001; tibial: r = -0.571, P = .004) and depolarizing threshold electrotonus at 90 to 100 ms (median: 0.424, P < .01; tibial: r = 0.435, P = .030). In contrast, there was no relationship between excitability values and nerve cross-sectional area in the type 2 cohort.

CONCLUSIONS

This study has identified correlation between markers of axonal membrane function and structural abnormalities in peripheral nerves of type 1 diabetes patients. The differential relationship in nerve function and structure between type 1 and type 2 diabetes provides clinical evidence that different pathophysiological mechanisms underlie the development of neuropathy in these patient groups.

Altered axonal excitability properties in facial palsy

INTRODUCTION

Axonal excitability measures give insight into the biophysical properties of peripheral nerve axons. In this study we applied these techniques to the study of facial palsy.

METHODS

Thirty patients with established facial palsy due to unresolved Bell's palsy or herpes zoster (>6 months duration), tumor invasion of the facial nerve, or traumatic facial nerve injury were assessed using facial nerve excitability techniques.

RESULTS

Full recordings were obtained in 23 patients (15 unrecovered Bell's palsy or herpes zoster, 5 trauma, 3 tumor-related). Compared with normal controls, the facial palsy group demonstrated changes in stimulus response properties, threshold electrotonus, refractoriness, superexcitability, and I/V slope. Depolarizing threshold electrotonus distinguished between viral and non-viral etiologies on subgroup analysis.

DISCUSSION

In this cross-sectional study, established facial palsy demonstrated findings similar to those seen in studies of regenerated axons. The improved understanding of underlying axonal characteristics offered by the technique may guide future treatment. Muscle Nerve 57: 268-272, 2018.

Association between glycemic variability and peripheral nerve dysfunction in type 1 diabetes

INTRODUCTION

Glycemic variability (GV) may be a novel factor in the pathogenesis of diabetic complications. However, the effect of GV on peripheral nerve function has not been explored systematically.

METHODS

The relationship between GV and acute glucose levels on motor and sensory nerve function in 17 patients with type 1 diabetes mellitus (T1DM) was assessed using continuous glucose monitoring and nerve excitability techniques to provide insight into the behavior of axonal voltage-gated ion channels. The mean amplitude of glycemic excursions (MAGE) was calculated to quantify GV.

RESULTS

MAGE strongly correlated with excitability markers of altered motor and sensory axonal function, including superexcitability (r = 0.54), S2 accommodation (r = -0.76), minimum current threshold (I/V) slope (r = 0.71), strength duration time constant (r = 0.66), and latency (r = 0.65; P <  0.05). Acute glucose levels did not correlate with markers of axonal function.

CONCLUSIONS

These findings suggest that GV may be an important mediator of axonal dysfunction in T1DM and a contributing factor in development of diabetic neuropathy. Muscle Nerve, 2016 Muscle Nerve 54: 967-969, 2016.

The Relationship between Dyslipidemia and Acute Axonal Function in Type 2 Diabetes Mellitus In Vivo

Objectives

Diabetic peripheral neuropathy (DPN) is a common and debilitating complication of diabetes mellitus. Treatment largely consists of symptom alleviation and there is a need to identify therapeutic targets for prevention and treatment of DPN. The objective of this study was to utilise novel neurophysiological techniques to investigate axonal function in patients with type 2 diabetes and to prospectively determine their relationship to serum lipids in type 2 diabetic patients.

Methods

Seventy-one patients with type 2 diabetes were consecutively recruited and tested. All patients underwent thorough clinical neurological assessments including nerve conduction studies, and median motor axonal excitability studies. Studies were also undertaken in age matched normal control subjects(n = 42). Biochemical studies, including serum lipid levels were obtained in all patients. Patient excitability data was compared to control data and linear regression analysis was performed to determine the relationship between serum triglycerides and low density lipoproteins and excitability parameters typically abnormal in type 2 diabetic patients.

Results

Patient mean age was 64.2±2.3 years, mean glycosylated haemoglobin (HbA1c%) was 7.8±0.3%, mean triglyceride concentration was 1.6±0.1 mmol/L and mean cholesterol concentration was 4.1±0.2mmol/L. Compared to age matched controls, median motor axonal excitability studies indicated axonal dysfunction in type 2 diabetic patients as a whole (T2DM) and in a subgroup of the patients without DPN (T2DM-NN). These included reduced percentage threshold change during threshold electrotonus at 10–20ms depolarising currents (TEd10–20ms)(controls 68.4±0.8, T2DM63.9±0.8, T2DM-NN64.8±1.6%,P<0.05) and superexcitability during the recovery cycle (controls-22.5±0.9, T2DM-17.5±0.8, T2DM-NN-17.3±1.6%,P<0.05). Linear regression analysis revealed no associations between changes in axonal function and either serum triglyceride or low density lipoprotein concentration when adjusted for renal function, a separate risk factor for neuropathy development. Our findings indicate that acutely, serum lipids do not exert an acute effect on axonal function in type 2 diabetic patients: TEd(10–20ms)(1.2(-1.4,3.8);P = 0.4) and superexcitability (2.4(-0.05, 4.8);P = 0.06).

Conclusions

These findings suggest that serum triglyceride levels are not related to axonal function in type 2 diabetic patients. Additional pathogenic mechanisms may play a more substantial role in axonal dysfunction prior to DPN development.

Neurological complications in chronic kidney disease

Patients with chronic kidney disease (CKD) are frequently afflicted with neurological complications. These complications can potentially affect both the central and peripheral nervous systems. Common neurological complications in CKD include stroke, cognitive dysfunction, encephalopathy, peripheral and autonomic neuropathies. These conditions have significant impact not only on patient morbidity but also on mortality risk through a variety of mechanisms. Understanding the pathophysiological mechanisms of these conditions can provide insights into effective management strategies for neurological complications. This review describes clinical management of neurological complications in CKD with reference to the contributing physiological and pathological derangements. Stroke, cognitive dysfunction and dementia share several pathological mechanisms that may contribute to vascular impairment and neurodegeneration. Cognitive dysfunction and dementia may be differentiated from encephalopathy which has similar contributing factors but presents in an acute and rapidly progressive manner and may be accompanied by tremor and asterixis. Recent evidence suggests that dietary potassium restriction may be a useful preventative measure for peripheral neuropathy. Management of painful neuropathic symptoms can be achieved by pharmacological means with careful dosing and side effect considerations for reduced renal function. Patients with autonomic neuropathy may respond to sildenafil for impotence. Neurological complications often become clinically apparent at end-stage disease, however early detection and management of these conditions in mild CKD may reduce their impact at later stages.

In vivo evidence of reduced nodal and paranodal conductances in type 1 diabetes

OBJECTIVES

Diabetic neuropathy is a debilitating complication of diabetes. Animal models of type 1 diabetes (T1DM) suggest that functional and structural changes, specifically axo-glial dysjunction, may contribute to neuropathy development. The present study sought to examine and characterise early sensory axonal function in T1DM patients in the absence of clinical neuropathy.

METHODS

Thirty patients with T1DM (15M:15F) without neuropathy underwent median nerve sensory and motor axonal excitability studies to examine axonal function. A verified mathematical model of human motor and sensory axons was used to elucidate the underlying causes of observed alterations.

RESULTS

Compared to controls (NC), T1DM patients demonstrated significant axonal excitability abnormalities in sensory and motor axons. These included marked reductions in sensory and motor subexcitability during the recovery cycle (T1DM 7.9 ± 0.4:10.4 ± 0.6%, NC 10.4 ± 0.7:15.4 ± 1.2%, P<0.01) and during hyperpolarizing threshold electrotonus at 10-20 ms (T1DM -75.5 ± 0.8:-69.7 ± 0.8%, NC -78.4 ± 1:-72.7 ± 0.9%, P<0.01). Mathematical modelling demonstrated that these changes were due to reduced nodal Na(+) currents, nodal/paranodal K(+) conductances and Na(+)/K(+) pump dysfunction, consistent with axo-glial dysjunction as outlined in animal models of T1DM.

CONCLUSIONS

The study provided support for the occurrence of early changes in nodal and paranodal conductances in patients with T1DM.

SIGNIFICANCE

These data indicate that axonal excitability techniques may detect early changes in diabetic patients, providing a window of opportunity for prophylactic intervention in T1DM.

Peripheral nerve axonal excitability studies: expanding the neurophysiologist's armamentarium

Nerve excitability studies have emerged as a recent novel non-invasive technique that offers complementary information to that provided by more conventional nerve conduction studies, the latter which provide only limited indices of peripheral nerve function. Such novel tools allow for the assessment of peripheral axonal biophysical properties that include ion channels, energy-dependent pumps and membrane potential in health and disease. With improvements in technique and development of protocols, a typical study can be completed in a short period of time and rapid measurement of multiple excitability indices can be achieved that provide insight into different aspects of peripheral nerve function. The advent of automated protocols for the assessment of nerve excitability has promoted their use in previous studies investigating disease pathophysiology such as in metabolic, toxic and demyelinating neuropathies, amyotrophic lateral sclerosis, stroke, spinal cord injury and inherited channelopathies. In more recent years, the use of nerve excitability studies have additionally provided insights into the pathophysiological mechanisms underlying cerebellar disorders that include stroke and familial cerebellar ataxias such as episodic ataxia types 1 and 2. Moreover, this technique may have diagnostic and therapeutic implications that may encompass a broader range of neurodegenerative cerebellar ataxias in years to come. In the foreseeable future, this technique may eventually be incorporated into clinical practice expanding the currently available armamentarium to the neurophysiologist.

Continuous subcutaneous insulin infusion preserves axonal function in type 1 diabetes mellitus

BACKGROUND

Diabetic peripheral neuropathy is a common and debilitating complication of diabetes mellitus. Although strict glycaemic control may reduce the risk of developing diabetic peripheral neuropathy, the neurological benefits of different insulin regimens remain relatively unknown.

METHODS

In the present study, 55 consecutive patients with type 1 diabetes mellitus underwent clinical neurological assessment. Subsequently, 41 non-neuropathic patients, 24 of whom were receiving multiple daily insulin injections (MDII) and 17 receiving continuous subcutaneous insulin infusion (CSII), underwent nerve excitability testing, a technique that assesses axonal ion channel function and membrane potential in human nerves. Treatment groups were matched for glycaemic control, body mass index, disease duration and gender. Neurophysiological parameters were compared between treatment groups and those taken from age and sex-matched normal controls.

RESULTS

Prominent differences in axonal function were noted between MDII-treated and CSII-treated patients. Specifically, MDII patients manifested prominent abnormalities when compared with normal controls in threshold electrotonus (TE) parameters including depolarizing TE(10-20ms), undershoot and hyperpolarizing TE (90-100 ms) (P < 0.05). Additionally, recovery cycle parameters superexcitability and subexcitability were also abnormal (P < 0.05). In contrast, axonal function in CSII-treated patients was within normal limits when compared with age-matched controls. The differences between the groups were noted in cross-sectional analysis and remained at longitudinal follow-up.

CONCLUSIONS

Axonal function in type 1 diabetes is maintained within normal limits in patients treated with continuous subcutaneous insulin infusion and not with multiple daily insulin injections. This raises the possibility that CSII therapy may have neuroprotective potential in patients with type 1 diabetes.

Assessing decreased sensation and increased sensory phenomena in diabetic polyneuropathies

Loss of sensation and increased sensory phenomena are major expressions of varieties of diabetic polyneuropathies needing improved assessments for clinical and research purposes. We provide a neurobiological explanation for the apparent paradox between decreased sensation and increased sensory phenomena. Strongly endorsed is the use of the 10-g monofilaments for screening of feet to detect sensation loss, with the goal of improving diabetic management and prevention of foot ulcers and neurogenic arthropathy. We describe improved methods to assess for the kind, severity, and distribution of both large- and small-fiber sensory loss and which approaches and techniques may be useful for conducting therapeutic trials. The abnormality of attributes of nerve conduction may be used to validate the dysfunction of large sensory fibers. The abnormality of epidermal nerve fibers/1 mm may be used as a surrogate measure of small-fiber sensory loss but appear not to correlate closely with severity of pain. Increased sensory phenomena are recognized by the characteristic words patients use to describe them and by the severity and persistence of these symptoms. Tests of tactile and thermal hyperalgesia are additional markers of neural hyperactivity that are useful for diagnosis and disease management.