An update on electrophysiological studies in neuropathy:

Sensory nerve conduction studies in probable painful neuropathy: comparing surface and near-nerve nerve conduction techniques

Introduction

We compared sensory nerve conduction studies (NCS) using surface and near-nerve recording electrodes in 53 patients with clinical probable painful neuropathy. Our aim was to validate the use of both recording techniques in that limited patient group.

Methods

Patients had sensory NCS using two established recording methods and quantitative sensory tests (QST). We compared normalised amplitudes of sensory sural nerve action potentials (SNAP) and sensory thresholds and used receiver operated curve (ROC) analysis of absolute SNAP amplitudes to find discriminatory levels predicting abnormal sensory thresholds.

Results

Mean sural SNAP z-scores differed depending on recording techniques (surface −1.0: SD 1.9; near-nerve −2.5: SD 1.7) with a numeric mean difference of −1.49 (Bland-Altman test: CI −1.872 to −1.12) with surface technique giving the z-value closest to zero. We documented a significant bias between the methods. Fifteen patients (28.3%) and 30 (56.6%) patients had abnormal results, respectively (χ2 test: p<0.001).

Sural SNAP amplitudes correlated significantly with vibration thresholds using the near-nerve (p<0.02) but not using the surface technique (p=0.11).

ROC analysis gave an optimal discriminative value of SNAP amplitudes for each QST measure, which were similar to our lower limit of normal values from investigating normal controls using near-nerve but not surface recording.

Conclusion

In patients with probable painful neuropathy, choosing sensory NCS technique introduces a bias in the diagnostic outcome. Differences in test performance suggest that using a normal sural NCS alone to delineate small fibre neuropathy from mixed neuropathy could result in poorly defined diagnostic groups.

Structural and functional brain abnormalities in postherpetic neuralgia: A systematic review of neuroimaging studies

In recent decades, an increasing number of neuroimaging studies utilizing magnetic resonance imaging (MRI) have explored the differential effects of postherpetic neuralgia (PHN) on brain structure and function. We systematically reviewed and integrated the findings from relevant neuroimaging studies in PHN patients. A total of 15 studies with 16 datasets were ultimately included in the present study, which were categorized by the different neuroimaging modalities. The results revealed that PHN was closely associated with structural/microstructural and functional abnormalities of the brain mainly located in the 'pain matrix', including the thalamus, insula, parahippocampus, amygdala, dorsolateral prefrontal cortex, precentral gyrus and inferior parietal lobe, as well as other regions, such as the precuneus, lentiform nucleus and brainstem. Furthermore, a disruption of multiple networks, including the default-mode network, salience network and limbic system, may contribute to the neurophysiological mechanisms underlying PHN. The findings indicate that the cerebral abnormalities of PHN were not restricted to the pain matrix but extended to other regions, profoundly affecting the regulation and moderation of pain processing in PHN. Future prospective and longitudinal neuroimaging studies with larger samples will elucidate the progressive trajectory of neural changes in the pathophysiological process of PHN.

Utility of electrodiagnostic studies in patients referred with a diagnosis of polyneuropathy

BACKGROUND

Peripheral polyneuropathies (PN) are common neuromuscular conditions. The role of electrodiagnostic study (EDX) in diagnosis of PN is not well-defined.

METHODS

We performed a retrospective chart review of patients referred for EDX evaluation of PN.

RESULTS

Of 162 patients analyzed, 23 had pure peripheral neuropathy (pPN; 14.2%), 29 had peripheral neuropathy and another diagnosis (PN+; 17.9%), 51 had an alternative diagnosis (nonPN; 31.5%), and 59 had normal studies (36.4%). In univariable analysis, age (P < .001) and gender (P = .004) were weakly associated with final diagnosis. In multinomial logistic regression analysis, significant predictors included age (odds ratio [OR] for nonPN/PN+:1.07 per year; 95% confidence interval [CI], 1.03-1.11), gender (OR for PN+:0.2, 95% CI, 0.07-0.61), and diabetes/prediabetes (OR for pPN:3.29; 95% CI, 1.17-9.27).

CONCLUSIONS

These data suggest that EDX commonly yields additional or nonPNs in patients referred with a diagnosis of PN, and although some variables predict electrodiagnosis, none have a large enough effect to suggest poor utility in any subpopulation.

Vincristine-induced peripheral neuropathy in survivors of childhood acute lymphoblastic leukaemia

BACKGROUND

Vincristine, an essential component of childhood acute lymphoblastic leukaemia (ALL) therapeutic protocols, is associated with dose-dependent neurotoxicity, but its long-term morbidity in treated children has not been clearly elucidated. The aim of this study is to determine the prevalence of vincristine-induced peripheral neuropathy (VIPN) among Malaysian childhood ALL survivors and its impact on motor function and quality of life.

PROCEDURE

Survivors of childhood ALL aged 4-18 years who had completed chemotherapy for 2 years or more were evaluated for VIPN using both the clinical Total Neuropathy Score (cTNS) and nerve conduction studies. Motor function and quality of life of the survivors were assessed via the Bruininks-Oseretsky Test of Motor Proficiency Brief Form, Second Edition (BOT-2 Brief Form) and the Paediatric Quality of Life version 4.0 Generic Core Scales (PedsQL4.0) questionnaire, respectively.

RESULTS

One hundred and one survivors with a duration of follow-up ranging from 2.0 to 10.3 years were recruited. Twenty-seven (26.7%) had abnormal cTNS scores and 69 (68.3%) had electrophysiological evidence of neuropathy. Of these, 16 (15.8%) had combined clinical and electrophysiological neuropathy (VIPN). Those previously treated on the intermediate- or high-risk treatment stratification arms had a higher risk of developing VIPN (67.3 vs. 32.7%; odds ratio [OR]: 9.06, 95% confidence interval [CI]: 1.14-71.86; P = 0.014). Survivors with VIPN had significantly lower quality of life scores in the physical (P = 0.024) and social domains (P = 0.039) compared with peers without VIPN, but no association with poorer motor function was observed.

CONCLUSIONS

Sixteen percent of ALL survivors had VIPN. VIPN should be increasingly recognised as a late effect of chemotherapy, as it significantly affects physical and social function quality of life.

Comparative pre-emptive analgesic efficacy study of novel antiepileptic agents gabapentin, lamotrigine and topiramate in patients undergoing major surgeries at a tertiary care hospital: a randomized double blind clinical trial

BACKGROUND

Surgical injury leads to postoperative pain hypersensitivity preceded by central nervous sensitization, due to lowered pain threshold in peripheral nociceptors and increased excitability of the spinal neurons. Pre-emptive analgesia is intended to decrease pain perception and overall analgesic need by use of drug regimen seizing central nervous system sensitization before exposure to painful stimuli. Earlier, few studies support pre-emptive analgesic efficacy of novel antiepileptic agent gabapentin. But topiramate and lamotrigine though proven analgesic in animal models of chronic pain and clinical studies of gabapentin resistant neuropathic pain; literature search revealed scarce data on its pre-emptive analgesic efficacy. The present study is designed to study and compare the pre-emptive analgesic efficacy of lamotrigine, topiramate and gabapentin (as control) in postoperative pain control.

METHODS

This randomized clinical trial included 90 patients of either sex, between 18 and 70 years undergoing major surgeries. Patients were randomly allocated into control and test groups and received respective treatment 30 min before induction of anesthesia. Aldrete's score and pain score were recorded using visual analogue scale and facial and behavioral rating scales at awakening and at 1, 2, 4, 6 and 24 h. Postoperative rescue analgesic consumption for 24 h was recorded. Data were analyzed using OpenEpi and SciStatCalc statistical softwares.

RESULTS

Significantly higher pain scores were observed in the topiramate group postoperatively for 2 h on all pain scales (p<0.05). Lamotrigine-treated patients were more comfortable throughout the study with significantly less (p<0.05) postoperative analgesic requirement comparable to gabapentin.

CONCLUSIONS

Study results are strongly suggestive of pre-emptive analgesic efficacy of single oral dose lamotrigine comparable to gabapentin and superior to topiramate in postoperative pain control.

The dilemma of diabetes in chronic inflammatory demyelinating polyneuropathy

PURPOSE

We reviewed the literature on chronic inflammatory demyelinating polyneuropathy (CIDP) in diabetes mellitus (DM) and explored real-world data on the prevalence and treatment of CIDP within DM.

METHODS

A literature search of Scopus was performed for the terms chronic inflammatory demyelinating polyradiculoneuropathy, chronic inflammatory demyelinating polyneuropathy, CIDP, and prevalence, incidence, epidemiology, or diabetes; peripheral neuropathy and prevalence or diabetes. We also searched through the reference lists of the resulting publications for additional findings that may have been missed. Additional publications on guidelines for the diagnosis of CIDP and diabetic neuropathy were also included. A descriptive analysis of the 2009-2013 PharMetrics Plus™ Database was performed to estimate the prevalence and treatment of CIDP within the DM population.

RESULTS

There is an increasing body of literature suggesting that the prevalence of CIDP tends to be higher in diabetic patients, especially in those of older age. Our real-world data seem to support published findings from the literature. For the total cohort (N=101,321,694), the percent prevalence of CIDP (n=8,173) was 0.008%; DM (n=4,026,740) was 4%. The percent prevalence of CIDP without DM (n=5,986) was 0.006%; CIDP with DM (n=2,187) was 9-fold higher at 0.054%. For patients >50years old, there was a significantly higher percentage of CIDP with DM than CIDP without DM. Approximately 50% of CIDP patients were treated with IVIg, 23%-24% with steroids, 1%-2% with PE, and 20%-23% received no treatment.

CONCLUSIONS

In addition to the growing evidence of higher prevalence of CIDP in DM, our findings reinforce the need for heightened awareness of the association of CIDP and DM.

Serum Phosphorylated Neurofilament-Heavy Chain, a Potential Biomarker, is Associated With Peripheral Neuropathy in Patients With Type 2 Diabetes

Neurofilament (NF), one of the major axonal cytoskeletal proteins, plays a critical role in degenerative diseases in both the central and the peripheral nervous systems. The aim of this study is to explore the relationship between serum phosphorylated neurofilament-heavy chain (pNF-H) and diabetic peripheral neuropathy (DPN) in patients with type 2 diabetes.Serum pNF-H concentrations were measured by ELISA in hospitalized patients with and without DPN (n = 118). DPN was assessed by clinical symptoms, signs, and electromyography.Compared with the non-DPN group (311.98 [189.59-634.12] pg/mL), the confirmed group (605.99 [281.17-1332.78] pg/mL) patients had the higher serum pNF-H levels (P = 0.007). DPN was significantly correlated with C-peptide (r = -0.269), total cholesterol (TC) (r = 0.185), and pNF-H (r = 0.258). Serum pNF-H levels were independently associated with DPN (P = 0.004), even after adjusting for age, sex, duration of diabetes, fasting plasma glucose, glycosylated hemoglobin A1c, TC, C-peptide, urinary albuminto/creatinine ratio, and estimated glomerular filtration rate. Compared with pNF-H quartile 1 (referent), patients in quartile 3 (odds ratio [OR], 3.977; 95% confidence interval [CI], 1.243-12.728; P = 0.021) and quartile 4 (OR, 10.488; 95% CI, 3.020-34.429; P = 0.000) had the higher risk of DPN after adjusting for the confounders.Serum pNF-H levels might be associated with the DPN, and the correlationship between serum pNF-H and DPN should be further studied.

The adjuvant effect of hypertension upon diabetic peripheral neuropathy in experimental type 2 diabetes

Type 2 diabetes (DM) is the most common cause of peripheral neuropathy in the Western world. A comorbidity, hypertension, has been speculated to contribute to initiation or worsening of diabetic peripheral neuropathy. We studied adult rat models using genetic strains with DM (Zucker Diabetic Fat rats)±hypertension (HTN (ZSF-1 rats)) to investigate the relative contributions of DM and HTN and the potential for additive effects of HTN upon existing DM for the development of peripheral neuropathy. Long duration sensorimotor behavioral and electrophysiological testing was complemented by histological and molecular methods. Only DM led to tactile and thermal hyperalgesia and affected motor nerve electrophysiology. Although DM led to marked loss of sensory amplitudes and to sensory conduction slowing, a mild additive effect from HTN contributed after 6months of DM with worsening of slowing of sensory nerve conduction velocities, but without effect upon sensory amplitudes. At the sensory dominant sural nerve, mild (<10%) but greater degrees of myelin thinning were noted with DM and HTN combined, suggesting a mild additive effect. Matrix metalloproteinase (MMP) expression was increased only at the sural nerve in the presence of HTN with co-localization to Schwann cells and myelin. The effects of DM and HTN upon peripheral nerve are dissimilar, with HTN contributing to MMP upregulation at the sites of myelin thinning at sensory nerve fibers, potentially worsening comorbid DM. Together, our results indicate that HTN has a mild additive contribution to diabetic peripheral neuropathy at sensory peripheral nerve fibers manifesting with the loss of myelin thickness.

Omega-conotoxins as experimental tools and therapeutics in pain management

Neuropathic pain afflicts a large percentage of the global population. This form of chronic, intractable pain arises when the peripheral or central nervous systems are damaged, either directly by lesion or indirectly through disease. The comorbidity of neuropathic pain with other diseases, including diabetes, cancer, and AIDS, contributes to a complex pathogenesis and symptom profile. Because most patients present with neuropathic pain refractory to current first-line therapeutics, pharmaceuticals with greater efficacy in pain management are highly desired. In this review we discuss the growing application of ω-conotoxins, small peptides isolated from Conus species, in the management of neuropathic pain. These toxins are synthesized by predatory cone snails as a component of paralytic venoms. The potency and selectivity with which ω-conotoxins inhibit their molecular targets, voltage-gated Ca²⁺ channels, is advantageous in the treatment of neuropathic pain states, in which Ca²⁺ channel activity is characteristically aberrant. Although ω-conotoxins demonstrate analgesic efficacy in animal models of neuropathic pain and in human clinical trials, there remains a critical need to improve the convenience of peptide drug delivery methods, and reduce the number and severity of adverse effects associated with ω-conotoxin-based therapies.

Venom peptides as a rich source of cav2.2 channel blockers

Ca_v2.2 is a calcium channel subtype localized at nerve terminals, including nociceptive fibers, where it initiates neurotransmitter release. Ca_v2.2 is an important contributor to synaptic transmission in ascending pain pathways, and is up-regulated in the spinal cord in chronic pain states along with the auxiliary α2δ1 subunit. It is therefore not surprising that toxins that inhibit Ca_v2.2 are analgesic. Venomous animals, such as cone snails, spiders, snakes, assassin bugs, centipedes and scorpions are rich sources of remarkably potent and selective Ca_v2.2 inhibitors. However, side effects in humans currently limit their clinical use. Here we review Ca_v2.2 inhibitors from venoms and their potential as drug leads.

[Electromyography (EMG) and neurography in patients with severe neuromuscular diseases]

BACKGROUND

Many neuromuscular diseases are potentially severe, and EMG and neurography are methods used in the assessment of these conditions.

METHOD

The article is based on the authors' knowledge and experience, with special emphasis on the use of these methods in the assessment of severe diseases affecting striated muscle and peripheral nerves. A PubMed search was performed with the cut-off fifteen years back in time, and in addition a discretionary selection was made of articles known to the authors.

RESULTS

EMG is the most valuable method for assessing myopathy, and neurography provides most information about neuropathy, but the methods are complementary. These examinations are the most sensitive for diagnosing some conditions (for example myasthaenia) A high level of expertise is necessary for diagnosing these conditions.

INTERPRETATION

EMG and neurography are important and often necessary means of assessing patients with severe neuromuscular disease.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

Sensitivity and specificity of von Frey's hairs for the diagnosis of peripheral neuropathy in patients with type 2 diabetes mellitus

OBJECTIVE

The aim was to evaluate von Frey's hairs as a diagnostic tool for peripheral neuropathy in type-2 diabetes patients with symptoms typical for diabetic neuropathy with respect to nerve conduction studies (NCSs) and a combination of clinical examination and NCS.

PATIENTS AND METHODS

65 patients with type-2 diabetes (33 men) with mean age 62.1 (SD 6.5) years, mean diabetes duration 17.5 (SD 9) years and mean symptom duration 5.2 (SD 4.3) years were examined with the set of von Frey's hairs. Diabetic neuropathy was diagnosed trough Neuropathy Disability Score (NDS). NCSs were performed on ulnar, peroneal, tibial and sural nerves.

RESULTS

Sensitivity of von Frey's hairs vs. NCS as the gold standard ranged from 37% to 79% and specificity from 65% to 87%. Sensitivity vs. combination of NDS and NCS ranged from 38% to 85% and specificity from 62% to 85%.

CONCLUSIONS

Von Frey's hairs have moderate sensitivity and specificity for diagnosis of neurophysiological and also clinical neuropathy. Being a fast and easy-to-perform procedure, they could be appropriate as a screening test in clinical practice.

Diabetes-induced myelin abnormalities are associated with an altered lipid pattern: protective effects of LXR activation

Diabetic peripheral neuropathy (DPN) is characterized by myelin abnormalities; however, the molecular mechanisms underlying such deficits remain obscure. To uncover the effects of diabetes on myelin alterations, we have analyzed myelin composition. In a streptozotocin-treated rat model of diabetic neuropathy, analysis of sciatic nerve myelin lipids revealed that diabetes alters myelin's phospholipid, FA, and cholesterol content in a pattern that can modify membrane fluidity. Reduced expression of relevant genes in the FA biosynthetic pathway and decreased levels of the transcriptionally active form of the lipogenic factor sterol-regulatory element binding factor-1c (SREBF-1c) were found in diabetic sciatic nerve. Expression of myelin's major protein, myelin protein zero (P0), was also suppressed by diabetes. In addition, we confirmed that diabetes induces sciatic nerve myelin abnormalities, primarily infoldings that have previously been associated with altered membrane fluidity. In a diabetic setting, synthetic activator of the nuclear receptor liver X receptor (LXR) increased SREBF-1c function and restored myelin lipid species and P0 expression levels to normal. These LXR-modulated improvements were associated with restored myelin structure in sciatic nerve and enhanced performance in functional tests such as thermal nociceptive threshold and nerve conduction velocity. These findings demonstrate an important role for the LXR-SREBF-1c axis in protection from diabetes-induced myelin abnormalities.

Utility of the cutaneous silent period in patients with diabetes mellitus

We performed this study to evaluate whether or not the cutaneous silent period (CSP) is a useful metric to identify small-fiber neuropathy in diabetic patients. The CSP was measured from the abductor pollicis brevis muscle in 30 healthy controls and 110 diabetic patients, who in turn were divided into 3 subgroups (patients with large-fiber neuropathy, patients with small-fiber neuropathy, and asymptomatic patients). The measured CSP and clinical characteristics were compared among the groups. The power of the CSP in discriminating patients from controls and any correlation with other clinical variables were analyzed. Each patient subgroup had a significantly delayed CSP latency compared to the controls. The latency of patients with large-fiber neuropathy was also significantly prolonged compared to the other subgroups of patients. The CSP latency was the only variable to discriminate patients. The latency showed a significant correlation with the late responses in nerve conduction studies. Thus, the CSP latency may be a useful tool in evaluating small neural fiber function in diabetic patients.

Formalin-induced short- and long-term modulation of Cav currents expressed in Xenopus oocytes: an in vitro cellular model for formalin-induced pain

Xenopus oocytes expressing high voltage-gated calcium channels (Ca(v)) were exposed to formalin (0.5%, v/v, 5 min.) and the oocyte death and Ca(v) currents were studied for up to 10 days. Ca(v) channels were expressed with alpha(1)beta(1)b and alpha(2)delta sub-units and the currents (I(Ba)) were studied by voltage clamp. None of the oocytes was dead during the exposure to formalin. Oocyte death was significant between day 1 and day 5 after the exposure to formalin and was uniform among the oocytes expressing various Ca(v) channels. Peak I(Ba) of all Ca(v) and A(1), the inactivating current component was decreased whereas the non-inactivated R current was not affected by 5 min. exposure to formalin. On day 1 after the exposure to formalin, Ca(v)1.2c currents were increased, 2.1 and 2.2 currents were decreased and 2.3 currents were unaltered. On day 5, both peak I(Ba) and A(1) currents were increased. Ca(v)1.2c, 2.2 and 2.3 currents were increased and Ca(v)2.1 was unaltered on day 10 after the exposure to formalin. Protein kinase C (PKC) may be involved in formalin-induced increase in Ca(v) currents due to the (i) requirement for Ca(v)beta(1)b sub-units; (ii) decreased phorbol-12-myristate,13-acetate potentiation of Ca(v)2.3 currents; (iii) absence of potentiation of Ca(v)2.3 currents following down-regulation of PKC; and (iv) absence of potentiation of Ca(v)2.2 or 2.3 currents with Ser-->Ala mutation of Ca(v)alpha(1)2.2 or 2.3 sub-units. Increased Ca(v) currents and PKC activation may coincide with changes observed in in vivo pain investigations, and oocytes incubated with formalin may serve as an in vitro model for some cellular mechanisms of pain.

Role of voltage-gated calcium channels in ascending pain pathways

Voltage gated calcium channels (VGCCs) are well established mediators of pain signals in primary afferent neurons. N-type calcium channels are localized to synaptic nerve terminals in laminae 1 and 2 of the dorsal horn where their opening results in the release of neurotransmitters such as glutamate and substance P. The contribution of N-type channels to the processing of pain signals is regulated by alternate splicing of the N-type channel gene, with unique N-type channel splice variants being expressed in small nociceptive neurons. In contrast, T-type VGCCs of the Ca(v)3.2 subtype are likely localized to nerve endings where they regulate cellular excitability. Consequently, inhibition of N-type and Ca(v)3.2 T-type VGCCs has the propensity to mediate analgesia. T-type channel activity is regulated by redox modulation, and can be inhibited by a novel class of small organic blockers. N-type VGCC activity can be potently inhibited by highly selective peptide toxins that are delivered intrathecally, and the search for small organic blockers with clinical efficacy is ongoing. Here, we provide a brief overview of recent advances in this area, as presented at the Spring Pain Research conference (Grand Cayman, 2008).

Signaling complexes of voltage-gated calcium channels and G protein-coupled receptors

Activation of opioid or opioid-receptor-like (ORL1 a.k.a. NOP or orphanin FQ) receptors mediates analgesia through inhibition of N-type calcium channels in dorsal root ganglion (DRG) neurons (1, 2). Unlike the three types of classical mu, delta, and kappa opioid receptors, ORL1 mediates an agonist-independent inhibition of N-type calcium channels. This is mediated via the formation of a physical protein complex between the receptor and the channel, which in turn allows the channel to effectively sense a low level of constitutive receptor activity (3). Further inhibition of N-type channel activity by activation of other G protein-coupled receptors is thus precluded. ORL1 receptors, however, also undergo agonist-induced internalization into lysosomes, and channels thereby become cointernalized in a complex with ORL1. This then results in removal of N-type channels from the plasma membrane and reduced calcium entry (4). Similar signaling complexes between N-type channels and GABA(B) receptors have been reported (5). Moreover, both L-type and P/Q-type channels appear to be able to associate with certain types of G protein-coupled receptors (6, 7). Hence, interactions between receptors and voltage-gated calcium channels may be a widely applicable means to optimize receptor channel coupling.

Diabetic polyneuropathy is associated with respiratory muscle impairment in type 2 diabetes

AIMS/HYPOTHESIS

Diabetes has a major negative effect on intensive care unit outcome. This has been partly attributed to impaired respiratory neuromuscular function. However, data on respiratory neuromuscular involvement in diabetes are lacking. This study therefore aimed to assess respiratory neuromuscular function related to diabetic polyneuropathy in patients with type 2 diabetes.

METHODS

Respiratory neuromuscular function was assessed by the use of volitional tests and twitch mouth (TwPmo) and twitch transdiaphragmatic (TwPdi) pressures during non-volitional bilateral anterior magnetic phrenic nerve stimulation in 21 male type 2 diabetic patients without pulmonary disease and in 23 healthy, well-matched controls (forced expiratory volume in 1 s 103 +/- 11 vs 103 +/- 12% predicted; p = 0.9).

RESULTS

Both volitionally assessed maximal inspiratory and expiratory mouth pressures, and sniff nasal and transdiaphragmatic pressures were comparable between diabetic patients and controls (p > 0.1 for all). TwPmo was reduced in diabetic patients compared with controls (1.3 +/- 0.5 vs 1.0 +/- 0.4 kPa; p = 0.04), while TwPdi was comparable (1.7 +/- 0.5 vs 1.6 +/- 0.7 kPa; p = 0.6). Following subgroup analysis, patients with no or mild polyneuropathy (n = 10) as assessed by neurological disability scoring had normal respiratory neuromuscular function, whereas patients with moderate or severe polyneuropathy (n = 11) presented with markedly impaired respiratory neuromuscular function as indicated by TwPmo (1.3 +/- 0.4 vs 0.8 +/- 0.3 kPa; p = 0.01) and TwPdi (1.9 +/- 0.6 vs 1.1 +/- 0.4 kPa; p < 0.01).

CONCLUSIONS/INTERPRETATION

With regard to volitional tests, diabetes does not affect respiratory neuromuscular function. In contrast, the application of non-volitional phrenic nerve stimulation provides strong evidence that diabetic polyneuropathy, as simply assessed by neurological disability scoring, is associated with substantially impaired respiratory neuromuscular function in type 2 diabetic patients.

Evaluation of polyneuropathy markers in type 1 diabetic kidney transplant patients and effects of islet transplantation: neurophysiological and skin biopsy longitudinal analysis

OBJECTIVE

The purpose of this study was to evaluate whether islet transplantation may stabilize polyneuropathy in uremic type 1 diabetic patients (end-stage renal disease [ESRD] and type 1 diabetes), who received a successful islet-after-kidney transplantation (KI-s).

RESEARCH DESIGN AND METHODS

Eighteen KI-s patients underwent electroneurographic tests of sural, peroneal, ulnar, and median nerves: the nerve conduction velocity (NCV) index and amplitudes of both sensory action potentials (SAPs) and compound motor action potentials (CMAPs) were analyzed longitudinally at 2, 4, and 6 years after islet transplantation. Skin content of advanced glycation end products (AGEs) and expression of their specific receptors (RAGE) were also studied at the 4-year follow-up. Nine patients with ESRD and type 1 diabetes who received kidney transplantation alone (KD) served as control subjects.

RESULTS

The NCV score improved in the KI-s group up to the 4-year time point (P = 0.01 versus baseline) and stabilized 2 years later, whereas the same parameter did not change significantly in the KD group throughout the follow-up period or when a cross-sectional analysis between groups was performed. Either SAP or CMAP amplitudes recovered in the KI-s group, whereas they continued worsening in KD control subjects. AGE and RAGE levels in perineurium and vasa nervorum of skin biopsies were lower in the KI-s than in the KD group (P < 0.01 for RAGE).

CONCLUSIONS

Islet transplantation seems to prevent long-term worsening of polyneuropathy in patients with ESRD and type 1 diabetes who receive islets after kidney transplantation. No statistical differences between the two groups were evident on cross-sectional analysis. A reduction in AGE/RAGE expression in the peripheral nervous system was shown in patients receiving islet transplantation.

Sensitivity and specificity of a new indicator test (Neuropad) for the diagnosis of peripheral neuropathy in type 2 diabetes patients: a comparison with clinical examination and nerve conduction study

OBJECTIVE

The objective of this study was to evaluate the sensitivity and specificity of a new indicator test (Neuropad) for the diagnosis of peripheral neuropathy in type 2 diabetes patients as compared with clinical examination and nerve conduction study (NCS).

PATIENTS AND METHODS

This study included 120 type 2 diabetes patients (58 men) with a mean age of 67.3 +/- 5.9 years and a mean diabetes duration of 13.1 +/- 3.2 years. Diabetic neuropathy was diagnosed through the Neuropathy Disability Score. An NCS was performed on radial, ulnar, sural, and common and deep peroneal nerves. Patients were also examined with the new indicator test. The "time to complete color change of the test" from blue to pink was recorded. The test was considered abnormal in patients who exhibited a time to complete color change of the test exceeding 600 s in at least one foot.

RESULTS

Neuropathy was diagnosed by clinical examination in 83 (69.2%) patients. The sensitivity of the indicator test for clinical neuropathy was 95.2%, and its specificity was 67.6%. The sensitivity of NCS for clinical neuropathy was 94%, and its specificity was 62.1%. The sensitivity of the indicator test for abnormal NCS was 97.8%, and its specificity was 96.4%.

CONCLUSIONS

The new indicator test has a very high sensitivity not only for the diagnosis of clinical neuropathy but also for the diagnosis of neurophysiological neuropathy. Specificity is moderately high for the diagnosis of clinical neuropathy, while it is particularly high for the diagnosis of neurophysiological neuropathy. The indicator test has a validity comparable to that of NCS for the diagnosis of diabetic neuropathy. Finally, the time to complete color change of the test is associated with the severity of nerve conduction impairment.

SREBP-1c expression in Schwann cells is affected by diabetes and nutritional status

Our previous work demonstrated that the sterol response element binding proteins (SREBP)-1 and SREBP-2, which are the key regulators of storage lipid and cholesterol metabolism respectively, are highly expressed in Schwann cells of adult peripheral nerves. In order to evaluate the role of Schwann cell SREBPs in myelination and functioning of peripheral nerves we have determined their expression during development, after fasting and refeeding, and in a rodent model of diabetes. Our results show that SREBP-1c and SREBP-2, unlike SREBP-1a, are the major forms of SREBPs present in peripheral nerves. The expression profile of SREBP-2 follows the expression of genes involved in cholesterol biosynthesis, while SREBP-1c is co-expressed with genes involved in storage lipid metabolism. In addition, the expression of SREBP-1c in the endoneurial compartment of peripheral nerves depends on nutritional status and is disturbed in type 1 diabetes. In line with this, insulin elevates the expression of SREBP-1c in primary cultured Schwann cells by activating the SREBP-1c promoter. Taken together, these findings reveal that SREBP-1c expression in Schwann cells responds to metabolic stimuli including insulin and that this response is affected in type 1 diabetes mellitus. This suggests that disturbed SREBP-1c regulated lipid metabolism may contribute to the pathophysiology of diabetic peripheral neuropathy.

Opioid, cheating on its receptors, exacerbates pain

Opioids are commonly thought of as compounds that alleviate pain. A new study finds that elevated levels of the opioid dynorphin can unexpectedly activate bradykinin receptors, contributing to the maintenance of neuropathic pain.

Validation of a novel point-of-care nerve conduction device for the detection of diabetic sensorimotor polyneuropathy

OBJECTIVE

The diagnosis of diabetic sensorimotor polyneuropathy using objective electrophysiological tests is hindered by limited access to the specialized laboratories and technicians that perform and interpret them. We evaluated the performance characteristics of a novel portable and automated point-of-care nerve conduction study device, which can be operated by nontechnical personnel, and compared it with conventional nerve conduction studies performed in a specialist setting.

RESEARCH DESIGN AND METHODS

Seventy-two consecutive patients with diabetes (8 type 1, 64 type 2) from a diabetes and a neuropathy outpatient clinic were evaluated concurrently with conventional nerve conduction studies (the reference standard) and the point-of-care device for sural nerve function (sural nerve amplitude potentials in microvolts [microV]).

RESULTS

Sural nerve amplitude potentials measured by the point-of-care device shared very strong correlation with the reference standard (Spearman's correlation coefficient 0.95, P < 0.001). The Bland and Altman method yielded agreement despite a small systematic underestimation by the point-of-care device of 1.2 +/- 3.4 microV. Despite this small systematic bias, the sensitivity and specificity of normal and abnormal sural nerve amplitude potentials measured by the point-of-care device for the detection of diabetic sensorimotor polyneuropathy defined by standard clinical and electrophysiological criteria were 92 and 82%, respectively.

CONCLUSIONS

A novel point-of-care device has excellent diagnostic accuracy for detecting electrophysiological abnormality in the sural nerve of patients who have diabetes. This automated device represents an alternative to conventional nerve conduction studies for the diagnosis of diabetic sensorimotor polyneuropathy.

Electrodiagnostic pattern approach for childhood polyneuropathies

Electrophysiologic studies play a key role in the detection and characterization of the pattern in childhood polyneuropathies. In this study, the etiologic profile of 74 children with polyneuropathy was prospectively evaluated based on the electrophysiologic studies. Five electrodiagnostic patterns were identified in the cohort: (1) acute axonal polyneuropathy (n: 32, 43%); (2) chronic axonal polyneuropathy (n: 16, 22%); (3) demyelinating motor and sensory polyneuropathy (n: 13, 17%); (4) pure sensory polyneuropathy (n: 11, 15%); (5) high-low syndrome (n: 2, 3%). Etiologic factors were identified in all of the patients with three electrodiagnostic patterns of polyneuropathy: acute axonal, pure sensory, and high-low syndrome. However, etiologic factors could not be determined in 5 (31%) children with chronic axonal polyneuropathy and in 3 (23%) children with demyelinating sensory and motor polyneuropathy. Among children with the acute axonal pattern, toxic causes were evident in 18 (56%), acute motor axonal neuropathy in 11 (35%), and acute motor sensory axonal polyneuropathy in 3 (9%). Nine (82%) patients with pure sensory polyneuropathy had diabetes mellitus. In conclusion, a thorough history and physical examination in conjunction with specific electrodiagnostic patterns might provide a cost-effective and rational differential diagnosis of childhood polyneuropathies.

Small-Fiber Neuropathy Associated with Capecitabine (Xeloda)-induced Hand-foot Syndrome: A Case Report

Hand-foot syndrome commonly results from treatment with capecitabine and is associated with pain, dysesthesias, paresthesias, and temperature intolerance. The cause of these symptoms in hand-foot syndrome has not been determined. We present the clinical, electrophysiologic, and biopsy data from a patient with capecitabine-induced hand-foot syndrome as supporting evidence implicating small-fiber neuropathy as the cause of these neuropathic symptoms. A patient with stage 4 breast cancer who develops capecitabine-induced hand-foot syndrome is referred for clinical and electrophysiologic testing. Intraepidermal nerve fiber density is assessed. Clinical evaluation demonstrates markedly decreased pain and temperature sensation with preserved strength, proprioception, and light touch. Standard electrodiagnostic testing is normal. The assessment of epidermal nerve fiber density demonstrates marked small-fiber loss both proximally and distally. In conclusion, small-fiber neuropathy is a likely cause of the neuropathic symptoms encountered in capecitabine-induced hand-foot syndrome. Similar clinical, electrophysiologic, and pathologic assessments are needed to confirm this finding in larger populations.

Muscle weakness: a progressive late complication in diabetic distal symmetric polyneuropathy

The aim of the study was to determine the progression of muscle weakness in long-term diabetes and its relation to the neuropathic condition. Thirty patients were recruited from a cohort of 92 diabetic patients who participated in a study on muscular function 6-8 years earlier. Nine subjects were nonneuropathic, 9 had asymptomatic neuropathy, and 12 had symptomatic neuropathy. Thirty matched control subjects who participated in the initial studies were also included. At follow-up, isokinetic dynamometry at the ankle, electrophysiological studies, vibratory perception thresholds, and clinical examination (neuropathy symptom score and neurological disability score [NDS]) were repeated. The annual decline of strength at the ankle was 0.7 +/- 1.7% in control subjects, 0.9 +/- 1.9% in nonneuropathic patients, 0.7 +/- 3.1% in asymptomatic neuropathic patients, and 3.2 +/- 2.3% in symptomatic neuropathic patients. In the symptomatic patients, the decline of muscle strength at the ankle was significant when compared with matched control subjects (P = 0.002) and with the other diabetic groups (P = 0.023). Also, the annual decline of muscle strength at the ankle was related to the combined score of all measures of neuropathy (r = -0.42, P = 0.03) and to the NDS (r = -0.52, P = 0.01). In patients with symptomatic diabetic neuropathy, weakness of ankle plantar and dorsal flexors is progressive and related to the severity of neuropathy.

Long current impulses may be required for nerve stimulation in patients with ischemic pain

PURPOSE

To report on the efficacy of peripheral plexus catheters in the treatment of ischemic pain in spite of nerve stimulation with long current impulses.

CLINICAL FEATURES

Two patients with severe neuropathic ischemic foot pain are described. A 56-yr-old man with diabetes, renal failure, and autonomic neuropathy presented with severe ischemic foot pain. Opioids produced excess sedation and hypotension. A 62-yr-old woman was admitted after femoral-popliteal bypass and developed a reperfusion pain syndrome not relieved with opioids, gabapentin, amitryptiline, and clonidine. In both patients, a sciatic plexus catheter was placed with resolution of pain. Conventional nerve stimulation, which uses a pulse duration of 0.1 msec, did not result in muscle contraction. However, by using a nerve stimulator capable of delivering a 1.0 msec impulse duration, a muscle twitch or paresthesia endpoint ensued allowing for successful catheter placement.

CONCLUSION

Peripheral plexus catheters provide a safe alter-native to systemic analgesics for pain relief in patients with ischemic foot pain. However, conventional nerve stimulation techniques may not elicit a motor response in patients with underlying neuropathy, and the use of nerve stimulators capable of delivering long current impulses is recommended.

Trigeminal neuralgia in a patient with multiple sclerosis and chronic inflammatory demyelinating polyneuropathy

BACKGROUND

Trigeminal neuralgia (TN) is characterized by unilateral, severe, brief, stabbing, recurrent pain in the distribution of one or more branches of the fifth cranial nerve. Symptomatic or secondary TN involves TN-like pain that develops owing to a central nervous system lesion (benign or malignant) or to multiple sclerosis (MS).

CASE DESCRIPTION

The authors present a report of a unique case of a 43-year-old patient with unilateral TN, MS and concomitant chronic inflammatory demyelinating polyneuropathy. The facial pain preceded any other manifestations of the systemic disorders, and only after repeated neurological examinations were these diagnoses established.

CLINICAL IMPLICATIONS

Magnetic resonance imaging of the brain and repeated neurological evaluations should be implemented in all patients with TN to rule out the presence of underlying disease. The dental practitioner should be familiar with TN to avoid unnecessary dental interventions and ensure prompt initiation of appropriate treatment.

Thermoreceptive innervation of human glabrous and hairy skin: a contact heat evoked potential analysis

The human palm has a lower heat detection threshold and a higher heat pain threshold than hairy skin. Neurophysiological studies of monkeys suggest that glabrous skin has fewer low threshold heat nociceptors (AMH type 2) than hairy skin. Accordingly, we used a temperature-controlled contact heat evoked potential (CHEP) stimulator to excite selectively heat receptors with C fibers or Adelta-innervated AMH type 2 receptors in humans. On the dorsal hand, 51 degrees C stimulation produced painful pinprick sensations and 41 degrees C stimuli evoked warmth. On the glabrous thenar, 41 degrees C stimulation produced mild warmth and 51 degrees C evoked strong but painless heat sensations. We used CHEP responses to estimate the conduction velocities (CV) of peripheral fibers mediating these sensations. On hairy skin, 41 degrees C stimuli evoked an ultra-late potential (mean, SD; N wave latency: 455 (118) ms) mediated by C fibers (CV by regression analysis: 1.28 m/s, N=15) whereas 51 degrees C stimuli evoked a late potential (N latency: 267 (33) ms) mediated by Adelta afferents (CV by within-subject analysis: 12.9 m/s, N=6). In contrast, thenar responses to 41 and 51 degrees C were mediated by C fibers (average N wave latencies 485 (100) and 433 (73) ms, respectively; CVs 0.95-1.35 m/s by regression analysis, N=15; average CV=1.7 (0.41) m/s calculated from distal glabrous and proximal hairy skin stimulation, N=6). The exploratory range of the human and monkey palm is enhanced by the abundance of low threshold, C-innervated heat receptors and the paucity of low threshold AMH type 2 heat nociceptors.

Understanding neuropathic pain

Neuropathic pain is defined as a chronic pain condition that occurs or persists after a primary lesion or dysfunction of the peripheral or central nervous system. Traumatic injury of peripheral nerves also increases the excitability of nociceptors in and around nerve trunks and involves components released from nerve terminals (neurogenic inflammation) and immunological and vascular components from cells resident within or recruited into the affected area. Action potentials generated in nociceptors and injured nerve fibers release excitatory neurotransmitters at their synaptic terminals such as L-glutamate and substance P and trigger cellular events in the central nervous system that extend over different time frames. Short-term alterations of neuronal excitability, reflected for example in rapid changes of neuronal discharge activity, are sensitive to conventional analgesics, and do not commonly involve alterations in activity-dependent gene expression. Novel compounds and new regimens for drug treatment to influence activity-dependent long-term changes in pain transducing and suppressive systems (pain matrix) are emerging.

The electrophysiological findings of subclinical neuropathy in patients with recently diagnosed type 1 diabetes mellitus

To assess the prevalence of subclinical neuropathy within the first year of type 1 diabetes mellitus, 30 patients and 14 healthy subjects have been studied prospectively. The patients whose diabetes duration was longer than 1 year have been excluded from the study. Control group consisted of healthy volunteers. Subjective neuropathy symptoms, neurological examination, and electrophysiological findings were evaluated. All patients were clinically asymptomatic. At least two abnormal independent neurophysiological nerve parameters, which were required as the criterion of the peripheral nervous system subclinical involvement, were found as in 96.6% of diabetic patients in the first years. The percentages of abnormal electrophysiological parameters in different motor and sensory nerves were 86.7% in sural nerve, 83.3% in peroneal motor nerve, 73.3% in posterior tibial motor nerve, 66.7% in median motor nerve, 63.3% in ulnar motor nerve, 60% in median sensory nerve, and 46.7% in ulnar sensory nerve. While distal motor latency, F conduction time, and minimum F latency were the most frequent abnormal parameters in the upper extremity electrophysiological study; conduction velocity, minimum and mean F latencies, F conduction time were the most frequent abnormal parameters in the lower extremity. In all sensory nerve conduction studies, the most frequent abnormal parameter was the onset latency. In the autonomic sympathetic nerve electrophysiological study, plantar SSR latency was found significantly longer than the control group. In the lower extremity generally somatic motor fibres, sensory large fibres and sympathetic autonomic nerve fibres were found to be more affected. There is a correlation between HbA1c levels and nerve conduction velocity in posterior tibial and peroneal nerves. However, upper extremity nerve conduction dysfunction was not correlated with HbA1c value. Neither the duration of disease nor the age of the subject correlated with the nerve dysfunction.

Small fiber neuropathy: a common and important clinical disorder

Small fiber neuropathy (SFN) is a neuropathy selectively involving small diameter myelinated and unmyelinated nerve fibers. Interest in this disorder has considerably increased during the past few years. It is often idiopathic and typically presents with peripheral pain and/or symptoms of autonomic dysfunction. Diagnosis is made on the basis of the clinical features, normal nerve conduction studies (NCS) and abnormal specialized tests of small nerve fibers. Among others, these tests include assessment of epidermal nerve fiber density, temperature sensation tests for sensory fibers and sudomotor and cardiovagal testing (QSART) for autonomic fibers. Unless an underlying disease is identified, treatment is usually symptomatic and directed towards alleviation of neuropathic pain.