Small and large fiber neuropathy in those with type 1 and type 2 diabetes: a 5-year follow-up study

What does nerve ultrasound contribute to the evaluation of diabetic polyneuropathy over time? A prospective follow-up observational study of people with type 2 diabetes

AIMS

Studies using peripheral nerve ultrasound have shown moderate nerve enlargement in individuals with diabetic polyneuropathy (DPN). Neither extent, course, consistency, nor clinical significance of this finding is clear.

METHOD

We examined 156 people with type 2 diabetes mellitus using nerve ultrasound, nerve conduction studies, and clinical scores. 59 received a follow-up examination after one year and 43 patients after two years.

RESULTS

Increase of cross-sectional area (CSA) of the peripheral nerves in DPN was rather negligible compared to normative cut-off values. The CSA of the median nerve at the forearm and wrist and the ulnar nerve at the upper arm, forearm and wrist were significantly larger in individuals with DPN compared to those without DPN. People with DPN had significant changes in most parameters of nerve conduction studies. Ultrasound measurements over time showed a slight increase in CSA in the median nerve at the carpal tunnel and a slight decrease in the fibular nerve at the fibular head. Ultrasound pattern sum score slightly decreased in the DPN group over two years.

CONCLUSIONS

Ultrasound measurements alone may be insufficient to detect DPN. Follow up with nerve ultrasound over one or two years was short and did not show substantial changes.

Pin-prick (Medipin) assessment for neuropathy in diabetes: Prospective screening study in primary care

AIMS

Diabetic patients are at elevated risk of neuropathy; early detection is desirable to minimise the risk of complications. The Medipin pin-prick device was appraised as a screening tool for diabetic neuropathy.

METHODS

Prospective cross-sectional comparative screening study in primary care setting, involving 389 participants with type 2 diabetes mellitus. The Medipin pin-prick method, involving dorsal application on the hallux of both feet, was compared to 10 g monofilament testing.

RESULTS

The ternary and semi-quantitative approach for scoring Medipin pin-prick sensation give very similar results (Spearman rho 0.67, P < 0.001). A total of 59 % patients had no signs of neuropathy (sharp sensation), 38 % reported impaired sensation (dull sensation), and an absence of sensation occurred in 3 % of patients. For the monofilament dorsal method, the figures were 79 % no neuropathy, 14 % elevated risk, and 7 % neuropathy respectively, and with the monofilament plantar method 87 % of patients had no neuropathy and 13 % did. Correlation analyses showed that taller patients and those with existing neuropathic pain are at very modest increased risk of neuropathy.

CONCLUSIONS

The Medipin pin-prick device can identify diabetic neuropathy and detects (first signs of) neuropathy in relatively more patients than 10 g monofilament testing. The differential targeting of nerve types, namely predominant small (Medipin) versus large (monofilament) fibre, likely underpins the difference in outcomes.

SIRT3 alleviates painful diabetic neuropathy by mediating the FoxO3a-PINK1-Parkin signaling pathway to activate mitophagy

INTRODUCTION

Painful diabetic neuropathy (PDN) is a common complication of diabetes. Previous studies have implicated that mitochondrial dysfunction plays a role in the development of PDN, but its pathogenesis and mechanism have not been fully investigated.

METHODS

In this study, we used high-fat diet/low-dose streptozotocin-induced rats as a model of type 2 diabetes mellitus. Behavioral testing, whole-cell patch-clamp recordings of dorsal root ganglion (DRG) neurons, and complex sensory nerve conduction velocity studies were used to assess peripheral neuropathy. Mitochondrial membrane potential (MMP), ATP, tissue reactive oxygen species, and transmission electron microscopy were used to evaluate the function and morphology of mitochondria in DRG. Real-time PCR, western blot, and immunofluorescence were performed to investigate the mechanism.

RESULTS

We found that damaged mitochondria were accumulated and mitophagy was inhibited in PDN rats. The expression of sirtuin 3 (SIRT3), which is an NAD+-dependent deacetylase in mitochondria, was inhibited. Overexpression of SIRT3 in DRG neurons by intrathecally administered LV-SIRT3 lentivirus ameliorated neurological and mitochondrial dysfunctions. This was evidenced by the reversal of allodynia and nociceptor hyperexcitability, as well as the restoration of MMP and ATP levels. Overexpression of SIRT3 restored the inhibited mitophagy by activating the FoxO3a-PINK1-Parkin signaling pathway. The effects of SIRT3 overexpression, including the reversal of allodynia and nociceptor hyperexcitability, the improvement of impaired mitochondria and mitophagy, and the restoration of PINK1 and Parkin expression, were counteracted when FoxO3a siRNA was intrathecally injected.

CONCLUSION

These results showed that SIRT3 overexpression ameliorates PDN via activation of FoxO3a-PINK1-Parkin-mediated mitophagy, suggesting that SIRT3 may become an encouraging therapeutic strategy for PDN.

Sensory Phenotypes Provide Insight Into the Natural Course of Diabetic Polyneuropathy

We aimed to investigate the characteristics and longitudinal course of sensory phenotypes identified through quantitative sensory testing (QST) in the frame of diabetic sensorimotor polyneuropathy (DSPN). A total of 316 individuals with diabetes were examined (type 2 diabetes 78.8%), 250 of whom were undergoing follow-up visits at 1, 2, and/or 4 (2.88 ± 1.27) years. Allocation into four sensory phenotypes (healthy, thermal hyperalgesia [TH], mechanical hyperalgesia [MH], and sensory loss [SL]) at every time point was based on QST profiles of the right foot. Cross-sectional analysis demonstrated a gradual worsening of clinical and electrophysiological sensory findings and increased DSPN prevalence across the groups, culminating in SL. Motor nerve impairment was observed solely in the SL group. Longitudinal analysis revealed a distinct pattern in the developmental course of the phenotype (from healthy to TH, MH, and finally SL). Those with baseline MH exhibited the highest risk of transition to SL. Reversion to healthy status was uncommon and mostly observed in the TH group. Among those without DSPN initially, presence or future occurrence of SL was associated with a three- to fivefold higher likelihood of DSPN development. Our comprehensive longitudinal study of phenotyped patients with diabetes elucidates the natural course of DSPN. QST-based sensory examination together with other tools for phenotyping may be useful in determining the natural course of diabetic neuropathy to identify patients at high risk of DSPN and guide preventive and therapeutic interventions.

ARTICLE HIGHLIGHTS

The course of diabetic sensorimotor polyneuropathy (DSPN) development, from healthy status to overt DSPN, is poorly understood. We studied the characteristics and longitudinal appearance of lower-extremity sensory phenotypes (healthy, thermal hyperalgesia [TH], mechanical hyperalgesia [MH], and sensory loss [SL]) identified through quantitative sensory testing in individuals with diabetes. There was an increasing severity and patterned order of longitudinal appearance across healthy, TH, MH, and SL phenotypes. SL was most strongly associated with formal DSPN. Our findings provide insight into the natural history of DSPN. Sensory phenotyping can be implemented to identify high-risk individuals and those most likely to benefit from therapeutic interventions.

Temporal trend of small nerve fibre degeneration in people with and without type 2 diabetes mellitus

AIMS

We investigated the long-term temporal trend of intraepidermal nerve fibre density (IENFD) and the association between changes in IENFD and metabolic factors in individuals with and without type 2 diabetes.

METHODS

A total of 66 participants were enrolled in this longitudinal population-based study, at baseline consisting of 35 individuals (median 61 years) without diabetes and 31 individuals with type 2 diabetes mellitus. Participants underwent clinical and electrophysiological examinations, as well as a skin biopsy both at baseline and at the follow-up visit (mean 8.1 ± 0.5 years). IENFD was assessed in thin sections of 5 μm, stained with the protein gene product 9.5-antibody and compared between the groups.

RESULTS

IENFD decreased during the period in both groups, with a greater decline in the group without diabetes than in type 2 diabetes (-2.3 and -0.6 fibres/mm respectively; p < 0.001). While IENFD at baseline was significantly reduced in type 2 diabetes relative to people without (p < 0.001), no difference in IENFD was found between groups at the follow-up (p = 0.183). Linear mixed model analysis indicated that age, weight and HbA_1c were associated with decrease in IENFD in the total population (p < 0.007). IENFD also decreased with increasing age and weight, but not with HbA_1c , in the separate groups (p < 0.049).

CONCLUSIONS

Despite lower IENFD levels at baseline in type 2 diabetes, IENFD was equal between the groups at follow-up. A decrease in IENFD is to a limited extent affected by body weight, and HbA_1c , but age seems to be the long-term determinant of IENFD in an elderly population.

Diabetes Distal Peripheral Neuropathy: Subtypes and Diagnostic and Screening Technologies

Diabetes distal symmetrical peripheral neuropathy (DSPN) is the most prevalent form of neuropathy in industrialized countries, substantially increasing risk for morbidity and pre-mature mortality. DSPN may manifest with small-fiber disease, large-fiber disease, or a combination of both. This review summarizes: (1) DSPN subtypes (small- and large-fiber disease) with attention to clinical signs and patient symptoms; and (2) technological diagnosis and screening for large- and small-fiber disease with inclusion of a comprehensive literature review of published studies from 2015-present (N = 66). Review findings, informed by the most up-to-date research, advance critical understanding of DSPN large- and small-fiber screening technologies, including those designed for point-of-care use in primary care and endocrinology practices.

Redefining distal symmetrical polyneuropathy features in type 1 diabetes: a systematic review

Diabetic neuropathy is among the most frequent complications of both type 1 (T1DM) and type 2 diabetes (T2DM) and commonly manifests as a distal symmetrical polyneuropathy (DSPN). Despite evidence that T1DM- and T2DM-related DSPN are separate entities, most of our knowledge on diabetic DSPN derives from studies focused on type 2 diabetes. This systematic review provides an overview of current evidence on DSPN in T1DM, including its epidemiological, pathophysiological and clinical features, along with principal diagnostic tests findings. This review included 182 clinical and preclinical studies. The results indicate that DSPN is a less frequent complication in T1DM compared with T2DM and that distinctive pathophysiological mechanisms underlie T1DM-related DSPN development, with hyperglycemia as a major determinant. T1DM-related DSPN more frequently manifests with non-painful than painful symptoms, with lower neuropathic pain prevalence compared with T2DM-associated DSPN. The overt clinical picture seems characterized by a higher prevalence of large fiber-related clinical signs (e.g., ankle reflexes reduction and vibration hypoesthesia) and to a lesser extent small fiber damage (e.g., thermal or pinprick hypoesthesia). These findings as a whole suggest that large fibers impairment plays a dominant role in the clinical picture of symptomatic T1DM-related DSPN. Nevertheless, small fiber diagnostic testing shows high diagnostic accuracy in detecting early nerve damage and may be an appropriate diagnostic tool for disease monitoring and screening.

Corneal confocal microscopy: A useful tool for diagnosis of small fiber neuropathy in type 2 diabetes

AIM

To investigate the diagnostic utility of corneal confocal microscopy (CCM) for small fiber neuropathy in type 2 diabetes.

MATERIALS AND METHODS

There were 186 participants with type 2 diabetes enrolled in this cross-sectional research. Pure small fiber neuropathy and mixed fiber neuropathy were defined using clinical examination, electromyography, and quantitative sensory testing. Demographics and clinical data, corneal confocal microscopy parameters, and other neuropathy measures were compared among the groups. The diagnostic utility of corneal confocal microscopy for small fiber neuropathy was assessed by the receiver operating curve.

RESULTS

Of the 186 patients, 24.7% had a pure small fiber neuropathy and 17.2% of patients were diagnosed with mixed fiber neuropathy. The corneal nerve fiber density (CNFD), corneal nerve fiber branch density (CNBD), and corneal nerve fiber length (CNFL) were significantly lower in subjects with pure small fiber neuropathy compared with those without diabetic peripheral neuropathy (all P < 0.05). The receiver operating curve analysis for corneal confocal microscopy diagnosing small fiber neuropathy demonstrated the area under the curve for CNFD of 0.791, CNFL of 0.778, CNBD of 0.710.

CONCLUSIONS

Patients with type 2 diabetes with pure small fiber neuropathy showed more corneal nerve loss compared with those without diabetic peripheral neuropathy. It was revealed that corneal confocal microscopy can be a reasonable marker in the diagnosis of small fiber neuropathy in type 2 diabetes.

Autonomic and Somatic Nerve Functions in Type 2 Diabetes Mellitus Patients: Electrophysiological Aspects

Objectives: To investigate the relationship between neurophysiological sensory and motor nerve function parameters, assessed by nerve conduction studies (NCS) with parasympathetic autonomic function and by heart rate variability (HRV) tests in patients with type 2 diabetes mellitus (T2DM). Material and Methods: A total of 161 T2DM patients underwent NCS. Cardiac autonomic response was assessed by HRV tests to deep breathing (HRV DB), to Valsalva manoeuvre, and during postural change from lying to standing. Results: The amplitude of motor response in the median nerve, tibial nerve, and peroneal nerve was associated with reduced HRV DB (p = 0.0001). The amplitude of motor response in the median nerve, tibial nerve, and peroneal nerve was associated with reduced HRV Valsalva (p = 0.0001). The correlation between the amplitude of response in all sensory nerves (sural, median, and ulnar) and HRV DB was statistically significant (p = 0.0001). Conclusion: The results indicate that there is a correlation in T2DM patients between the damage of small myelinated and unmyelinated nerve fibres from cardiac autonomic nerves, assessed by HRV tests and damage of large motor and sensory fibres, assessed by NCS. Based on the above results, a combination of NCS and HRV tests should be considered in the neurophysiological approach to diabetic neuropathy.

Progression and regression of nerve fibre pathology and dysfunction early in diabetes over 5 years

It has been traditionally suggested that the early development of diabetic sensorimotor polyneuropathy (DSPN) is characterized by a predominant and progressive injury to small nerve fibres followed by large fibre impairment. We alternatively hypothesized that small and large fibre damage due to DSPN in type 1 and type 2 diabetes could develop in parallel and may not only be progressive but also reversible. Participants from the German Diabetes Study baseline cohort with recent-onset type 1/type 2 diabetes (n = 350/570) and age-matched glucose-tolerant control individuals (Control 1/Control 2: n = 114/190) were assessed by nerve conduction studies (NCS), thermal detection thresholds (TDT), vibration perception threshold (VPT), Neuropathy Symptom Score (NSS), Neuropathy Disability Score (NDS), and intraepidermal nerve fibre density (IENFD) in skin biopsies (type 1/type 2 diabetes: n = 102/226; Control 1/Control 2: n = 109/208). Subsets of participants with type 1/type 2 diabetes were followed for 5 years (n = 184/307; IENFD subset: n = 18/69). DSPN was defined by the Toronto Consensus criteria. At baseline, DSPN was present in 8.1 and 13.3% of the type 1 and type 2 diabetes groups, respectively. The most frequently abnormal tests in the lower limbs below or above the 2.5th and 97.5th centile of the controls were IENFD (13.7%) and individual NCS (up to 9.4%) in type 1 diabetes participants and IENFD (21.8%), malleolar VPT (17.5%), and individual NCS (up to 11.8%) in those with type 2 diabetes, whereas TDT abnormalities did not differ between the control and diabetes groups. After 5 years in type 2 diabetes participants, the highest progression rates from the normal to the abnormal range were found for IENFD (18.8%) by -4.1 ± 2.8 fibres/mm, malleolar VPT (18.6%) by 9.1 ± 20.2 µm, and NDS (15.0%) by 3.7 ± 1.5 points, while vice versa the highest regression rates were observed for NDS (11.2%) by -3.1 ± 1.3 points, sural nerve amplitude (9.1%) by 4.7 ± 3.0 µV, IENFD (8.7%) by 1.4 ± 1.3 fibres/mm, and NSS (8.2%) by -5.8 ± 1.6 points. In type 1 diabetes participants, no major progression was seen after 5 years, but subclinical DSPN regressed in 10.3%. These findings point to an early parallel damage to both small and large nerve fibres in well-controlled recent-onset type 2 and, to a lesser extent, type 1 diabetes. After 5 years peripheral nerve morphology and function and clinical measures progress to the abnormal range in type 2 diabetes, but initial nerve alterations are also reversible to a meaningful degree.

Better Islet Function and Cardiovascular Autonomic Function in Chinese Type 2 Diabetic Patients with Pure Small Fiber Neuropathy than with Mixed Neuropathy

INTRODUCTION

The clinical characteristics and outcomes of small fiber neuropathy (SFN) in Chinese patients with type 2 diabetes mellitus (T2DM) have not been thoroughly described. In this study, we investigated the metabolic and neurological indexes and the prognosis of patients with T2DM based on skin biopsy.

METHODS

A total of 34 healthy Chinese volunteers were recruited for skin biopsy to establish the reference range of intra-epidermal nerve fiber density (IENFD), and 89 patients with T2DM attending the Nanjing Drum Tower Hospital were evaluated at baseline. Of these 89 patients, 17 with pure SFN and nine with mixed diabetic polyneuropathy (DPN) were reassessed at the end of the follow-up.

RESULTS

Glycated hemoglobin and postprandial blood glucose levels were lower (P = 0.005 and P = 0.041, respectively) and postprandial C-peptide and insulin levels were higher (P = 0.001 and P = 0.019, respectively) in the pure SFN group than in the mixed DPN group. A partial correlation study showed that there was a negative correlation between IENFD of the distal leg and cardiovascular autonomic reflex test (CART) scores (r = - 0.513, P = 0.001) after adjusting for age and duration of diabetes. Only vitamin B12 level (P = 0.028) and motor nerve conduction velocity (MCV) of the common peroneal nerve (P = 0.045) were increased in the patients with pure SFN at the final visit while MCVs of the common peroneal nerve (P = 0.025) and tibial nerve (P = 0.047) were decreased in the mixed DPN group at the final visit.

CONCLUSION

Better islet function and cardiovascular autonomic function were observed in patients with pure SFN compared with mixed DPN. The metabolic and neurological indexes remained relatively stable in the patients with pure SFN during the follow-up.

Quantitative vibration perception threshold in assessing diabetic polyneuropathy: Should the cut-off value be adjusted for Chinese individuals with type 2 diabetes?

AIMS/INTRODUCTION

To examine the performance and identify the optimal threshold of vibration perception threshold (VPT) for diagnosing diabetic polyneuropathy (DPN) in a Chinese population according to multiple definitions of DPN as gold standards.

MATERIALS AND METHODS

VPT was determined in 421 Chinese individuals with type 2 diabetes, who simultaneously completed a questionnaire of neuropathic symptoms, and underwent the assessment of signs of peripheral neuropathy and electromyography tests. Three definitions of DPN (i.e., clinician-diagnosed DPN, abnormal nerve conduction and confirmed DPN) were taken as reference gold standards.

RESULTS

Vibration perception threshold was a specific measure for all three groups of DPN outcomes, with the highest specificity noted for clinician-diagnosed DPN (85.1%). The specificity for abnormal nerve conduction and confirmed DPN was 77.0 and 76.6%, respectively. The sensitivity of VPT was 67.0% for clinician-diagnosed DPN, 66.5% for abnormal nerve conduction and 67.2% for confirmed DPN. The optimal cut-off threshold for abnormal nerve conduction, as well as confirmed DPN, was VPT >14.9 V. The specificity and sensitivity of VPT >14.9 V as the cut-off value for clinician-diagnosed DPN were 85.6 and 66.2%, respectively. When taking clinician-diagnosed DPN as the gold standard, the performance of VPT for diagnosing DPN was best with an area under the curve value of 0.804.

CONCLUSIONS

VPT measured using the neurothesiometer had relatively high specificity and best performance for diagnosing DPN when clinician-diagnosed DPN rather than abnormal nerve conduction was taken as the gold standard in a Chinese population. A VPT value of ≥15 V might be equally applicable for diagnosing DPN in a Chinese population.

Pathogenesis, diagnosis and clinical management of diabetic sensorimotor peripheral neuropathy

Diabetic sensorimotor peripheral neuropathy (DSPN) is a serious complication of diabetes mellitus and is associated with increased mortality, lower-limb amputations and distressing painful neuropathic symptoms (painful DSPN). Our understanding of the pathophysiology of the disease has largely been derived from animal models, which have identified key potential mechanisms. However, effective therapies in preclinical models have not translated into clinical trials and we have no universally accepted disease-modifying treatments. Moreover, the condition is generally diagnosed late when irreversible nerve damage has already taken place. Innovative point-of-care devices have great potential to enable the early diagnosis of DSPN when the condition might be more amenable to treatment. The management of painful DSPN remains less than optimal; however, studies suggest that a mechanism-based approach might offer an enhanced benefit in certain pain phenotypes. The management of patients with DSPN involves the control of individualized cardiometabolic targets, a multidisciplinary approach aimed at the prevention and management of foot complications, and the timely diagnosis and management of neuropathic pain. Here, we discuss the latest advances in the mechanisms of DSPN and painful DSPN, originating both from the periphery and the central nervous system, as well as the emerging diagnostics and treatments.

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of foot-sole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

The time to develop treatments for diabetic neuropathy

BACKGROUND

Diabetic neuropathy is a multifaceted condition affecting up to 50% of individuals with long standing diabetes. The most common presentation is peripheral diabetic sensory neuropathy (DPN).

METHODS

We carried out a systematic review of papers dealing with diabetic neuropathy on Pubmed in addition to a targeted Google search.Search terms included small fiber neuropathy,diffuse peripheral neuropathy, quantitative sensory testing, nerve conduction testing, intra-epidermal nerve fiber density, corneal confocal reflectance microscopy, aldose reductase inhbitors, nerve growth factor, alpha-lipoic acid, ruboxistaurin, nerve growth factor antibody, and cibinetide.

RESULTS

Over the past half century, there have been a number of agents undergoing unsuccessful trials for treatment of DPN.There are several approved agents for relief of pain caused by diabetic neuropathy, but these do not affect the pathologic process.

EXPERT OPINION

The failure to find treatments for diabetic neuropathy can be ascribed to (1) the complexity of design of studies and (2) the slow progression of the condition, necessitating long duration trials to prove efficacy.We propose a modification of the regulatory process to permit early introduction of agents with demonstrated safety and suggestion of benefit as well as prolongation of marketing exclusivity while long term trials are in progress to prove efficacy.

Early changes of nerve integrity in preclinical carriers of hereditary transthyretin Ala117Ser amyloidosis with polyneuropathy

BACKGROUND AND PURPOSE

Disease-modifying therapies provide new horizons for hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) to slow neuropathic progression. Initiating treatment at the earliest time requires biomarkers reflecting both small- and large-fiber degeneration in carriers.

METHODS

This study included examinations of pathology (intraepidermal nerve fiber [IENF] density), physiology (nerve conduction studies, autonomic function test, and nerve excitability), and psychophysics (thermal thresholds) in carriers to compare to healthy controls and asymptomatic diabetic patients.

RESULTS

There were 43 carriers (44.2 ± 11.4 years, p.Ala117Ser in 42 carriers), 43 controls (43.4 ± 12.7 years) including 26 noncarrier families, and 50 asymptomatic diabetic patients (58.1 ± 9.5 years). Carriers had lower IENF densities than controls and similar densities as diabetic patients. Median nerve conduction parameters, especially distal motor latency, were the most frequent neurophysiological abnormality in carriers, could differentiate carriers from controls and diabetic patients, were correlated with IENF densities in carriers but not in controls and diabetic patients, and were correlated with nerve excitability parameters in carriers but not in controls. Fifteen carriers (34.9%) with electrophysiological evidence of median nerve entrapment at the wrist had lower IENF densities and more abnormal conduction parameters than carriers without. We defined nerve dysfunction index-the ratio of median distal motor latency to IENF density-which differentiated carriers from controls.

CONCLUSIONS

In late-onset ATTRv-PN carriers with predominant p.Ala117Ser, median conduction parameters were the most common neurophysiological abnormalities and served as surrogate signatures of small- and large-fiber impairment. Combination of median distal motor latency and IENF density can reflect early neuropathy in carriers.

Advances in Screening, Early Diagnosis and Accurate Staging of Diabetic Neuropathy

The incidence of both type 1 and type 2 diabetes is increasing worldwide. Diabetic peripheral neuropathy (DPN) is among the most distressing and costly of all the chronic complications of diabetes and is a cause of significant disability and poor quality of life. This incurs a significant burden on health care costs and society, especially as these young people enter their peak working and earning capacity at the time when diabetes-related complications most often first occur. DPN is often asymptomatic during the early stages; however, once symptoms and overt deficits have developed, it cannot be reversed. Therefore, early diagnosis and timely intervention are essential to prevent the development and progression of diabetic neuropathy. The diagnosis of DPN, the determination of the global prevalence, and incidence rates of DPN remain challenging. The opinions vary about the effectiveness of the expansion of screenings to enable early diagnosis and treatment initiation before disease onset and progression. Although research has evolved over the years, DPN still represents an enormous burden for clinicians and health systems worldwide due to its difficult diagnosis, high costs related to treatment, and the multidisciplinary approach required for effective management. Therefore, there is an unmet need for reliable surrogate biomarkers to monitor the onset and progression of early neuropathic changes in DPN and facilitate drug discovery. In this review paper, the aim was to assess the currently available tests for DPN's sensitivity and performance.

3d phase-contrast nanotomography of unstained human skin biopsies may identify morphological differences in the dermis and epidermis between subjects

BACKGROUND

Enteric neuropathy is described in most patients with gastrointestinal dysmotility and may be found together with reduced intraepidermal nerve fiber density (IENFD). The aim of this pilot study was to assess whether three-dimensional (3d) imaging of skin biopsies could be used to examine various tissue components in patients with gastrointestinal dysmotility.

MATERIAL AND METHODS

Four dysmotility patients of different etiology and two healthy volunteers were included. From each subject, two 3-mm punch skin biopsies were stained with antibodies against protein gene product 9.5 or evaluated as a whole with two X-ray phase-contrast computed tomography (CT) setups, a laboratory µCT setup and a dedicated synchrotron radiation nanoCT end-station.

RESULTS

Two patients had reduced IENFD, and two normal IENFD, compared with controls. µCT and X-ray phase-contrast holographic nanotomography scanned whole tissue specimens, with optional high-resolution scans revealing delicate structures, without differentiation of various fibers and cells. Irregular architecture of dermal fibers was observed in the patient with Ehlers-Danlos syndrome and the patient with idiopathic dysmotility showed an abundance of mesenchymal ground substance.

CONCLUSIONS

3d phase-contrast tomographic imaging may be useful to illustrate traits of connective tissue dysfunction in various organs and to demonstrate whether disorganized dermal fibers could explain organ dysfunction.

Point-of-care nerve conduction device predicts the severity of diabetic polyneuropathy: A quantitative, but easy-to-use, prediction model

Aims/Introduction

A gold standard in the diagnosis of diabetic polyneuropathy (DPN) is a nerve conduction study. However, as a nerve conduction study requires expensive equipment and well‐trained technicians, it is largely avoided when diagnosing DPN in clinical settings. Here, we validated a novel diagnostic method for DPN using a point‐of‐care nerve conduction device as an alternative way of diagnosis using a standard electromyography system.

Materials and Methods

We used a multiple regression analysis to examine associations of nerve conduction parameters obtained from the device, DPNCheck™, with the severity of DPN categorized by the Baba classification among 375 participants with type 2 diabetes. A nerve conduction study using a conventional electromyography system was implemented to differentiate the severity in the Baba classification. The diagnostic properties of the device were evaluated using a receiver operating characteristic curve.

Results

A multiple regression model to predict the severity of DPN was generated using sural nerve conduction data obtained from the device as follows: the severity of DPN = 2.046 + 0.509 × ln(age [years]) − 0.033 × (nerve conduction velocity [m/s]) − 0.622 × ln(amplitude of sensory nerve action potential [µV]), r = 0.649. Using a cut‐off value of 1.3065 in the model, moderate‐to‐severe DPN was effectively diagnosed (area under the receiver operating characteristic curve 0.871, sensitivity 70.1%, specificity 87.7%, positive predictive value 83.0%, negative predictive value 77.3%, positive likelihood ratio 5.67, negative likelihood ratio 0.34).

Conclusions

Nerve conduction parameters in the sural nerve acquired by the handheld device successfully predict the severity of DPN.

Effects of type 1 diabetes on reflexive cardiovascular responses to intermittent muscle contraction

This is the first study to provide evidence that early-stage type 1 diabetes mellitus (T1DM) leads to an exaggerated exercise pressor reflex evoked by intermittent muscle contraction, resulting in substantially higher cardiovascular strain. These findings are significant as they indicate that interventions targeting the exercise pressor reflex may work to alleviate the increased cardiovascular strain and overall burden during exercise in T1DM.

Insulin Treatment Attenuates Small Nerve Fiber Damage in Rat Model of Type 2 Diabetes

INTRODUCTION

Current clinical guidelines for management of diabetic peripheral neuropathy (DPN) emphasize good glycemic control. However, this has limited effect on prevention of DPN in type 2 diabetic (T2D) patients. This study investigates the effect of insulin treatment on development of DPN in a rat model of T2D to assess the underlying causes leading to DPN.

METHODS

Twelve-week-old male Sprague-Dawley rats were allocated to a normal chow diet or a 45% kcal high-fat diet. After eight weeks, the high-fat fed animals received a mild dose of streptozotocin to induce hyperglycemia. Four weeks after diabetes induction, the diabetic animals were allocated into three treatment groups receiving either no insulin or insulin-releasing implants in a high or low dose. During the 12-week treatment period, blood glucose and body weight were monitored weekly, whereas Hargreaves' test was performed four, eight, and 12 weeks after treatment initiation. At study termination, several blood parameters, body composition, and neuropathy endpoints were assessed.

RESULTS

Insulin treatment lowered blood glucose in a dose-dependent manner. In addition, both doses of insulin lowered lipids and increased body fat percentage. High-dose insulin treatment attenuated small nerve fiber damage assessed by Hargreaves' test and intraepidermal nerve fiber density compared to untreated diabetes and low-dose insulin; however, neuropathy was not completely prevented by tight glycemic control. Linear regression analysis revealed that glycemic status, circulating lipids, and sciatic nerve sorbitol level were all negatively associated with the small nerve fiber damage observed.

CONCLUSION

In summary, our data suggest that high-dose insulin treatment attenuates small nerve fiber damage. Furthermore, data also indicate that both poor glycemic control and dyslipidemia are associated with disease progression. Consequently, this rat model of T2D seems to fit well with progression of DPN in humans and could be a relevant preclinical model to use in relation to research investigating treatment opportunities for DPN.

Evaluation of small nerve fiber dysfunction in type 2 diabetes

OBJECTIVES

To assess potential correlations between intraepidermal nerve fiber densities (IENFD), graded with light microscopy, and clinical measures of peripheral neuropathy in elderly male subjects with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and type 2 diabetes (T2DM), respectively.

MATERIALS AND METHODS

IENFD was assessed in thin sections of skin biopsies from distal leg in 86 men (71-77 years); 24 NGT, 15 IGT, and 47 T2DM. Biopsies were immunohistochemically stained for protein gene product (PGP) 9.5, and intraepidermal nerve fibers (IENF) were quantified manually by light microscopy. IENFD was compared between groups with different glucose tolerance and related to neurophysiological tests, including nerve conduction study (NCS; sural and peroneal nerve), quantitative sensory testing (QST), and clinical examination (Total Neuropathy Score; Neuropathy Symptom Score and Neuropathy Disability Score).

RESULTS

Absent IENF was seen in subjects with T2DM (n = 10; 21%) and IGT (n = 1; 7%) but not in NGT. IENFD correlated weakly negatively with HbA1c (r = -.268, P = .013) and Total Neuropathy Score (r = -.219, P = .042). Positive correlations were found between IENFD and sural nerve amplitude (r = .371, P = .001) as well as conduction velocity of both the sural (r = .241, P = .029) and peroneal nerve (r = .258, P = .018). Proportions of abnormal sural nerve amplitude became significantly higher with decreasing IENFD. No correlation was found with QST. Inter-rater reliability of IENFD assessment was good (ICC = 0.887).

CONCLUSIONS

Signs of neuropathy are becoming more prevalent with decreasing IENFD. IENFD can be meaningfully evaluated in thin histopathological sections using the presented technique to detect neuropathy.

Diagnostic criteria for small fibre neuropathy in clinical practice and research

The diagnostic criteria for small fibre neuropathy are not established, influencing the approach to patients in clinical practice, their access to disease-modifying and symptomatic treatments, the use of healthcare resources, and the design of clinical trials. To address these issues, we performed a reappraisal study of 150 patients with sensory neuropathy and a prospective and follow-up validation study of 352 new subjects with suspected sensory neuropathy. Small fibre neuropathy diagnostic criteria were based on deep clinical phenotyping, quantitative sensory testing (QST) and intraepidermal nerve fibre density (IENFD). Small fibre neuropathy was ruled out in 5 of 150 patients (3.3%) of the reappraisal study. Small fibre neuropathy was diagnosed at baseline of the validation study in 149 of 352 patients (42.4%) based on the combination between two clinical signs and abnormal QST and IENFD (69.1%), abnormal QST alone (5.4%), or abnormal IENFD alone (20.1%). Eight patients (5.4%) had abnormal QST and IENFD but no clinical signs. Further, 38 patients complained of sensory symptoms but showed no clinical signs. Of those, 34 (89.4%) had normal QST and IENFD, 4 (10.5%) had abnormal QST and normal IENFD, and none had abnormal IENFD alone. At 18-month follow-up, 19 of them (56%) reported the complete recovery of symptoms and showed normal clinical, QST and IENFD findings. None of those with one single abnormal test (QST or IENFD) developed clinical signs or showed abnormal findings on the other test. Conversely, all eight patients with abnormal QST and IENFD at baseline developed clinical signs at follow-up. The combination of clinical signs and abnormal QST and/or IENFD findings can more reliably lead to the diagnosis of small fibre neuropathy than the combination of abnormal QST and IENFD findings in the absence of clinical signs. Sensory symptoms alone should not be considered a reliable screening feature. Our findings demonstrate that the combined clinical, functional and structural approach to the diagnosis of small fibre neuropathy is reliable and relevant both for clinical practice and clinical trial design.

An update on the diagnosis and treatment of diabetic somatic and autonomic neuropathy

Diabetic peripheral neuropathy (DPN) is the most common chronic complication of diabetes. It poses a significant challenge for clinicians as it is often diagnosed late when patients present with advanced consequences such as foot ulceration. Autonomic neuropathy (AN) is also a frequent and under-diagnosed complication unless it is overtly symptomatic. Both somatic and autonomic neuropathy are associated with increased mortality. Multiple clinical trials have failed because of limited efficacy in advanced disease, inadequate trial duration, lack of effective surrogate end-points and a lack of deterioration in the placebo arm in clinical trials of DPN. Multifactorial risk factor reduction, targeting glycaemia, blood pressure and lipids can reduce the progression of DPN and AN. Treatment of painful DPN reduces painful symptoms by about 50% at best, but there is limited efficacy with any single agent. This reflects the complex aetiology of painful DPN and argues for improved clinical phenotyping with the use of targeted therapy, taking into account co-morbid conditions such as anxiety, depression and sleep disturbance.

Diagnosing Diabetic Neuropathy: Something Old, Something New

There are potentially many ways of assessing diabetic peripheral neuropathy (DPN). However, they do not fulfill U.S. Food and Drug Administration (FDA) requirements in relation to their capacity to assess therapeutic benefit in clinical trials of DPN. Over the past several decades symptoms and signs, quantitative sensory and electrodiagnostic testing have been strongly endorsed, but have consistently failed as surrogate end points in clinical trials. Therefore, there is an unmet need for reliable biomarkers to capture the onset and progression and to facilitate drug discovery in DPN. Corneal confocal microscopy (CCM) is a non-invasive ophthalmic imaging modality for in vivo evaluation of sensory C-fibers. An increasing body of evidence from multiple centers worldwide suggests that CCM fulfills the FDA criteria as a surrogate endpoint of DPN.

Clinical Characteristics, Electrophysiology, and Skin Biopsy of 38 Peripheral Neuropathy Cases with Small Fiber Involvement of Various Etiologies

Background:

In small fiber neuropathy (SFN), thinly myelinated Aδ and unmyelinated C fibers are primarily affected, resulting in sensory and/or autonomic symptoms. Various etiologies have been shown to be associated with SFN. This study was aimed to analyze a variety of features in peripheral neuropathy (PN) with small fiber involvement, and to compare disease severity among patients with idiopathic PN, PN associated with impaired glucose tolerance (IGT), and metabolic syndrome (MS) PN.

Methods:

Thirty-eight PN patients with small fiber involvement were enrolled from December 20, 2013 to May 31, 2016. Patients were divided into idiopathic PN, IGT-related PN, and MS-related PN groups. Detailed medical history and small fiber neuropathy were investigated, and symptom inventory questionnaire was conducted, as well as the visual analog scale. Nerve conduction studies and skin biopsies were also performed. The differences among the groups were analyzed using analysis of variance and Kruskal-Wallis test.

Results:

Eight patients were diagnosed with pure SFN. Intraepidermal nerve fiber density (IENFD) weakly correlated with motor conduction velocity (MCV) (r = 0.372, P = 0.025), and proximal (r = 0.383, P = 0.021) and distal (r = 0.358, P = 0.032) compound muscle action potential (CMAP) of the tibial nerve. IENFD also weakly correlated with MCV of the peroneal nerve (r = 0.399, P = 0.016). IENFD was shown to be significantly different among all groups (χ² = 9.901, P = 0.007). IENFD was significantly decreased (χ² = 23.000, P = 0.003) in the MS-related PN group compared to the idiopathic PN group. The MCV of the tibial nerve was significantly different among all groups (χ² = 8.172, P < 0.017). The proximal (F = 4.336, P = 0.021) and distal (F = 3.262, P = 0.049) CMAP of the tibial nerve was also significantly different among all groups.

Conclusions:

IENFD of patients included in the present study weakly correlated with various electrophysiological parameters. Small and large fibers are more involved in patients with MS-related PN than in patients with idiopathic PN.

Uric acid levels correlate with the severity of diabetic sensorimotor polyneuropathy

INTRODUCTION

Diabetic sensorimotor polyneuropathy (DSP) is the most frequent complication in patients with diabetes mellitus (DM), and is associated with age, DM duration, and HbA1c levels. In addition, higher uric acid (UA) levels are reported in patients with DSP.

OBJECTIVES

To explore whether UA levels correlate with DSP severity.

METHODS

We extracted the demographic data, clinical history, neurological and electrophysiological examinations and laboratory findings of 115 patients diagnosed with DSP from January 2012 to December 2015.

RESULTS

The mean age of the total cohort was 62±13years, with 61% men. A positive correlation was demonstrated between uric acid levels and increasing sensory symptoms, and more abnormal electrophysiological findings and vibration perception thresholds. In addition, correlations with gait abnormality, the presence of paraproteinemia and creatine kinase levels were found.

DISCUSSION

Our study results show that uric acid levels correlate with clinical and electrophysiological severity of DSP, providing additional evidence for the relationship between the two, and a potential therapeutic target for DSP.

An integrated perspective on diabetic, alcoholic, and drug-induced neuropathy, etiology, and treatment in the US

Neuropathic pain (NeuP) is a syndrome that results from damaged nerves and/or aberrant regeneration. Common etiologies of neuropathy include chronic illnesses and medication use. Chronic disorders, such as diabetes and alcoholism, can cause neuronal injury and consequently NeuP. Certain medications with antineoplastic effects also carry an exquisitely high risk for neuropathy. These culprits are a few of many that are fueling the NeuP epidemic, which currently affects 7%-10% of the population. It has been estimated that approximately 10% and 7% of US adults carry a diagnosis of diabetes and alcohol disorder, respectively. Despite its pervasiveness, many physicians are unfamiliar with adequate treatment of NeuP, partly due to the few reviews that are available that have integrated basic science and clinical practice. In light of the recent Centers for Disease Control and Prevention guidelines that advise against the routine use of μ-opioid receptor-selective opioids for chronic pain management, such a review is timely. Here, we provide a succinct overview of the etiology and treatment options of diabetic and alcohol- and drug-induced neuropathy, three different and prevalent neuropathies fusing the combined clinical and preclinical pharmacological expertise in NeuP of the authors. We discuss the anatomy of pain and pain transmission, with special attention to key ion channels, receptors, and neurotransmitters. An understanding of pain neurophysiology will lead to a better understanding of the rationale for the effectiveness of current treatment options, and may lead to better diagnostic tools to help distinguish types of neuropathy. We close with a discussion of ongoing research efforts to develop additional treatments for NeuP.

Four-year sequential nerve conduction changes since first visit in Japanese patients with early type 2 diabetes

Aims/Introduction

Despite being the most common complication of diabetes, the pattern of clinical development of diabetic neuropathy is not well‐known. In the present study, we retrospectively examined sequential changes in nerve conduction studies (NCS) for 4 years to characterize the way neuropathic changes develop in patients with type 2 diabetes.

Materials and Methods

We randomly selected 158 patients with type 2 diabetes who newly visited Naka Memorial Clinic, Ibaraki, Japan, and underwent serial 4‐year NCS. Records of clinical profile, signs and symptoms of neuropathy, and NCS data from median and tibial nerves were extracted to determine the progression of neuropathy. NCS data were represented by motor nerve conduction velocities, amplitudes of compound muscle action potentials (CMAPs) and minimal latencies of F‐wave.

Results

The prevalence of clinical neuropathy in 158 cases was 30% at baseline and 29% at the end of the study, with improvement of glycated hemoglobin (8.6–6.9%). Over 4 years, there were no changes of the signs and symptoms of neuropathy. Motor nerve conduction velocities were slightly improved or consistent at the fourth year compared with those at the beginning (+1.5% in median nerve, P < 0.05; +0.8%, not significant in the tibial nerve). The extent of the glycated hemoglobin correction correlated with the improvement of motor nerve conduction velocity. In contrast, CMAPs of both median and tibial nerves were decreased (−11.6%, P < 0.01; −3.7%, P < 0.05, respectively). For the decrease in CMAPs, no specific risk factors were identified by logistic regression analysis.

Conclusions

The present study showed progressive decline of CMAPs despite improved glycemic controls or the lack of NCV slowing in patients with early type 2 diabetes.