Medial plantar sensory response. Sensitive indicator of peripheral nerve dysfunction in patients with diabetes mellitus

Cross-Sectional Study of the Relationship Between Medial Plantar Nerve Conduction Studies and Severity of Diabetic Neuropathy

Objective

Diabetic peripheral neuropathy (DPN), a complication of diabetes, is detected only in later stages. Medial plantar nerve (MPL) can identify earlier stages of neuropathy. We evaluated the correlation of MPL sensory nerve action potentials (SNAPs) and severity of DPN measured using the Toronto Clinical Neuropathy Score (TCNS).

Methods

In this hospital-based, cross-sectional study, we recruited diabetic subjects referred for suspected DPN. Neuropathy was graded with TCNS. Sural nerve conduction studies were performed using standard techniques. MPL studies were conducted using the modified Ponsford technique. All evaluations were performed on Nihon Kohden (model MEB 9200K). Averaged MPL SNAP was correlated with TCNS using Pearson's correlation coefficient. To estimate a correlation of 0.4 with 80% power (P = 0.05), we needed 46 subjects. Linear regression was conducted to adjust for age, duration, and diabetic control. Receiver operating characteristic (ROC) curve analysis was performed to obtain the cutoff for MPL SNAP values using the Youden index.

Results

Fifty-one subjects with a mean age of 53.5 years (8.7) and mean duration of diabetes of 10.2 years (7.2) were included. MPL SNAPs were recordable in 12 patients, and the mean amplitude was 5.15 (2.9) µV. There was correlation between MPL SNAP and TCNS (r = -0.43, P = 0.02). No confounding was seen. Use of MPL SNAP resulted in diagnosis of DPN in an additional six (11.8%) patients. The ROC curve suggested that MPL SNAP cutoff of 1.05 µV had an accuracy of 67% in identifying neuropathy as defined by TCNS.

Conclusions

MPL SNAP has a moderate correlation with clinical score and identifies more diabetic neuropathy than sural nerve.

Medial plantar sensory nerve action potential: A study for reference data in Indian subjects

Context:

The medial plantar nerve (MP) sensory nerve action potential (SNAP) has been shown to be a sensitive indicator for detecting a length-dependent axonal peripheral neuropathy. However, literature survey shows paucity of age stratified data. This study was undertaken to obtain age stratified reference data for MP SNAP amplitude and latency.

Aim:

To establish age-stratified reference data in Indian subjects for the MP SNAP.

Study Setting and Design:

The study was conducted in the electrodiagnostic laboratory of a tertiary city hospital and is retrospective study.

Materials and Methods:

A retrospective study was conducted using the nerve conduction study reports of 173 patients with only upper limb symptoms and findings. Patients were between the ages of 18 and 86 years, stratified into six groups, a = 18-30 years, b = 31- 40 years, c = 41-50 years, d = 51- 60 years, e = 61-70 years, f ≥70 years.

Statistical Methods:

Stata 12.1 statistical program was used. Lower limit of the SNAP amplitude was obtained using mean-2SD of transformed data. Analysis of variance defined the intergroup variability, linear regression and Pearson's correlation assessed the statistical significance.

Results:

The lower limit of normal MP SNAP amplitude for each age group is as follows: a: 8.7uv b: 7.5uv c: 3.7 uv d: 2.9uv e: 2.0 uv f: 1.4uv. The amplitude difference between the groups b & c, c & d and e and f using analysis of variance with Bonferroni correction and Tukey post-hoc test was not significant, but the other groups showed statistically significant variance. The equation of regression for the predicted amplitude value with age was defined as Y^ = {3.5 + age (-.0233) – 2 (0.389)}³.

Conclusion:

This study provides age stratified reference data for MP SNAP. There is evidence to suggest that MP SNAP amplitude varies with age hence age stratified data should be used to define abnormality.

Electrophysiologic testing in diabetic neuropathy

Electrophysiologic studies provide objective data concerning nerve and muscle function. This information enables the diagnosis of disease states and monitoring of disease progression. This chapter describes the changes in electrophysiologic function in both prediabetes and diabetes and discusses the utility of this testing in patients with diabetes. Both the strengths and limitations of electrophysiology are discussed.

Comparison of diabetic neuropathy symptom score and medial plantar sensory nerve conduction studies in diabetic patients showing normal routine nerve conduction studies

OBJECTIVE

Diabetic Neuropathy Symptom (DNS) scoring and medial plantar NCS are useful methods for diagnosis of diabetic polyneuropathy (DPN). We evaluated the correlation between DNS score and medial plantar NCS in diabetic patients with a normal routine NCS.

METHOD

Nineteen healthy subjects were included as a control group. Fifty patients with diabetes mellitus who were referred for the evaluation of DPN were recruited (35 asymptomatic and 15 symptomatic). Control subjects and diabetic patients over the age of 70 were excluded from this study.

RESULTS

Medial plantar nerve action potential (NAP) was recordable in all 19 control subjects and was not obtainable in 7 out of 15 symptomatic patients and in 5 out of 35 asymptomatic patients. The amplitudes of sural (Spearman r=-0.293, p=0.003) and medial plantar NAP (Spearman r=-0.215, p=0.03) correlated with DNS score.

CONCLUSION

An abnormality finding in the medial plantar sensory nerve conduction study is a more sensitive indicator than sural nerve conduction study in the diagnosis of DPN and the medial plantar sensory nerve should be included in the evaluation of DPN in patients showing normal routine NCS.

Electrodiagnostic studies in the management and prognosis of neuromuscular disorders

Prognosis remains a neglected aspect of modern medical care and research, behind diagnosis and treatment. The very term "electrodiagnosis" implies as much. Despite this, much has been published regarding the use and benefit of electrodiagnostic techniques in assessing prognosis and assisting in management of patients after the diagnosis has been established. This information is often hidden or otherwise not emphasized. This review summarizes the literature regarding the use of such techniques for prognosis and management of disorders of lower motor neurons, peripheral nerves, neuromuscular transmission, and muscle.

Acquired peripheral neuropathy

The element of time is a crucial factor in the electrodiagnostic presentation of PN. The characteristic changes seen in various neuropathies evolve over time. If testing is performed very early in the course of the disease, abnormalities may not yet be present, in part, because the range of normal values for NCS parameters is broad. In addition, if the process is asymmetric, the affected nerves may not be sampled. Very late in the course of the disease, a multifocal process may appear diffuse and symmetric as the areas of focal involvement coalesce. A primarily, demyelinating process may begin to demonstrate secondary axonal involvement. In very severe neuropathies, it may become difficult to evoke any NCS responses to characterize the neuropathy. It is essential to place the electrodiagnostic findings within the context of the clinical progression to avoid drawing erroneous conclusions. Sometimes, the true nature of the neuropathy is clear only after sequential testing. The etiologic diagnoses of acquired polyneuropathy are vast. A well-crafted electrodiagnostic evaluation can categorize neuropathies into more specific diagnostic groups by identifying the descriptive diagnosis, significantly narrowing the list of possible etiologic diagnoses. Electrodiagnostic testing, which always starts with a pertinent history and physical examination, should always be viewed as a continuation and quantification of the physical examination. Only by knowing the extent and pattern of the clinical involvement is it possible to formulate a thorough electrodiagnostic evaluation. This knowledge is especially important in cases in which the presentation is multifocal, because the neuropathy can be missed entirely if the affected nerves are not evaluated. When evaluating a neuropathy, there are three important questions to answer: (1) Is the process diffuse or multifocal? (2) Is it demyelinating or axonal? (3) Does it predominantly involve the motor or sensory nerves? By assessing the neuropathy along these three axes, the large number of possible etiologic diagnoses becomes much more manageable.

Sixteenth annual AAEM Edward H. Lambert Lecture. Electrodiagnostic aspects of diabetic neuropathies: entrapments. American Association of Electrodiagnostic Medicine

A MEDLINE review suggested a lack of recent studies about the entrapments seen with underlying diabetic neuropathy. Suggested protocols for research in diabetic peripheral neuropathy have not included the concepts of entrapments as an early--indeed, first manifestation of the neuropathy. Carpal tunnel syndrome is a frequent accompaniment of diabetic peripheral neuropathy. Assessment of the degree of entrapment superimposed on the generalized peripheral neuropathy can be clarified by analysis of the CMAP and the SNAP--particularly with respect to duration of the negative spike of the action potential. Also, analysis of the action potentials elicited by stimulation of the ulnar and radial nerves and their comparison with the median nerve is often helpful. Finally careful inspection of the action potential when stimulating proximal and distal to the entrapment will establish the degree of nerve compromise relative to the underlying diabetic neuropathy.

Essential fatty acids prevent slowed nerve conduction in streptozotocin diabetic rats

Rats were given streptozotocin to induce insulin-dependent diabetes or citrate buffer alone in two experiments. Initially, the effect of 5 wks of dietary gamma-linolenic acid (GLA) plus eicosapentaenoic acid (EPA) on cutaneous nerve conduction velocity (CV) was examined. CV was determined by direct stimulation and recording from saphenous nerve under urethane anesthesia. Secondly, a 5 weeks study of supplementing the diet with GLA, GLA and EPA, or hydrogenated coconut oil (HC) was done. In addition, motor nerve CV was determined by directly stimulating sciatic nerve and recording from gastrocnemius muscle. The acute diabetes led to weight loss, and elevated blood glucose and glycosylated hemoglobin levels. Essential fatty acid (EFA) supplementation had no effect on any of these measures of severity of diabetes. In diabetic rats without EFA supplementation, CV of the myelinated fibers fell by 19-21%, while those receiving both GLA and EPA had normal CV. In diabetic rats receiving GLA alone, CV fell by 5-7%, which was significantly less than those without EFA supplementation (p less than 0.01 for cutaneous, and p less than 0.001 for motor nerves).

The correlation between sensory nerve conduction velocities and three metabolic indices in rats treated with streptozotocin

The fastest conduction velocities of the myelinated (A) and unmyelinated (C) sensory nerve fibres were measured in the saphenous nerves of rats made diabetic up to 5 weeks previously by injection of streptozotocin. The conduction velocity of the fastest A-alpha fibres in treated rats fell by 25% compared to control rats. The effect on the slow A-delta fibres was small but C-fibres were not affected. Levels of glycosylated haemoglobin, random plasma glucose, and the net changes in body weights were also measured. There were significant changes in these three metabolic indices among diabetic rats (p less than 0.001) and the three indices were inter-related. There was a good correlation between A-fibre conduction velocity and levels of glycosylated haemoglobin but no significant relationship between C-fibre conduction velocity and this metabolic index. A-fibre conduction velocity was statistically more correlated with levels of glycosylated haemoglobin than the other two metabolic indices (p less than 0.01).

The association between symptomatic sensory neuropathy and body stature in diabetic patients

In the diabetic patient the clinical manifestations of peripheral neuropathy occur more commonly in the distributions of longer neurons. Utilizing height as a proxy variable, we have examined whether neuron length is also a determinant for the occurrence of peripheral neuropathy among diabetic patients. In studies performed at two sites (Sheffield and Miami) the heights of diabetic patients with symptomatic peripheral neuropathy were compared with those of non-neuropathic diabetic patients. At each site the neuropathic patients were significantly taller (P = 0.02 for Sheffield and P = 0.01 for Miami). These data were not biased by age or race. Body stature (as a proxy for neuron length) appears to be a constitutional risk factor for diabetic peripheral neuropathy.

Comparison of the effects of continuous subcutaneous infusion and split-mixed injection of insulin on nerve function in type I diabetes mellitus

Comparable groups of type I diabetic patients (n = 19) were matched for age, duration of diabetes, mean HbA1 values, insulin requirements, degree of neuropathy, and the mean of nerve conduction velocities (CV) in median, ulnar, and peroneal motor and median, ulnar, and sural sensory nerves. One group (n = 9) was managed with continuous subcutaneous infusion of (regular) insulin (CSII); the other (n = 10) with split-mixed injections of (intermediate and regular) insulin (SMII). After 12 months, glucose regulation was equally and significantly improved in both groups (P less than 0.005), although it was not sufficiently intense to normalize mean total glycosylated hemoglobin values in either group. Furthermore treatment produced no difference between groups in the values for mean amplitude of glycemic excursions, 12 month average of consecutive M-values or in clinical evaluation. However, in the CSII group, mean CV had increased 6.4% (2.75 + 0.56 m/s; mean +/- SEM) versus 1.3% (0.57 +/- 0.54 m/s) in the SMII group (P less than 0.005). Multivariate analysis on a nerve-by-nerve basis found significantly improved conduction in 2/6 nerves (median motor; ulnar sensory) in the CSII group compared to the SMII group. These results suggest that CSII may provide a more favorable microenvironment for nerve repair.

Absence of the sensory action potential of the medial plantar nerve: a sensitive indicator of diabetic neuropathy

The sensory action potential of the medial plantar nerve (MPSAP), using needle recording electrodes subcutaneously, was measured in 119 patients with diabetes ((75 insulin-dependent, mean age 43.7 +/- 1.2 SEM years (range 15-73) and in 75 age-matched normal subjects (mean age 44.0 +/- 1.5 years (range 19-75)). The MPSAP was not detectable in 56 out of 119 diabetics; there was only one absent MPSAP response in the normal group, in a patient aged 71 years. Diabetics with absent MPSAP responses were significantly older, heavier and taller and had diabetes of longer duration. The amplitudes and conduction velocities in the sural, common peroneal, and tibial nerves were also significantly smaller. The amplitudes of the MPSAP, when present, correlated with height (r = -0.47(43), p less than 0.001), weight (r = -0.44(43), p less than 0.001), the distal tibial compound motor action potential (r = 0.37(43), p less than 0.01), and the common peroneal nerve conduction velocity (r = 0.32(43), p less than 0.02). The MPSAP was always absent if the sural SAP was less than 5uV but also in 14/59 patients whose sural SAP amplitudes were within 1 sd of the normal mean (greater than 10.7 uV). The MPSAP was absent at a younger age and with diabetes of shorter duration than is seen with unrecordable sural SAPs. It may therefore represent an early manifestation of neuropathy in diabetes.

The perception threshold to an electric stimulus deeply applied in the lower limbs in normal and diabetic subjects

The loss of sensitivity to nociceptive stimuli is one of the main factors involved in the pathogeny of diabetic gangrene. The aim of this study was to develop a simple and practical method for selecting the cases prone to such a complication. The perception threshold (either voltage, mV or current, microA) was determined in 137 randomly selected diabetic patients and 38 non-diabetic controls, by an original electronic device using sinusoidal waves, delivered through two electrode needles introduced at a depth of 0.5 cm at two points located on the anterior aspect of the shank about 12 cm apart. At each of the eight frequencies studied (10, 20, 50, 100, 200, 500, 1000 and 2000 Hz) three electrical parameters (voltage across the needle electrodes, the resistive and the capacitive current component) were recorded when the subject first perceived the stimulus. A significantly higher perception threshold was found in diabetic patients vs. non-diabetic subjects, at all frequencies studied and with all three electrical parameters recorded. A greater difference in the perception threshold between diabetic and non-diabetic subjects (a ratio higher than 3) was, however, found using the resistive component of the current and at frequencies higher than 200 Hz.

Increased nerve conduction in diabetics after a year of improved glucoregulation

We studied median, ulnar and peroneal motor nerve conduction velocity (NCV) and median sensory action potential (SAP) latency and amplitude in 18 insulin-dependent diabetic patients who were begun on a continuous subcutaneous insulin infusion (CSII) program. With institution of this therapy, significant decreases in mean blood glucose and glycosylated hemoglobin occurred. After 12 months of CSII treatment, median, peroneal, and ulnar motor NCVs all increased significantly. The average NCV increase was 2.5 m/s. Median SAP amplitude and latency did not significantly change. In a second group of 12 diabetic patients with the same mean age and comparable initial NCV and SAP measures, no significant changes in motor NCVs or SAPs occurred after 12 months of conventional insulin treatment. These results indicated the need for further long-term studies of the role of strict glucose control in the prevention of diabetic neuropathy.

Diabetes patient education: a health care provider perspective

Diabetes patient educa tion, a preventive health service, is an integral component of the overall program of care for the diabetic patient. Affecting both biomedical and psychosocial status, it may be analyzed through its knowledge- and behavior-based com ponents. Both are impor tant to the overall result, and each involves distinct provider knowledge and skills for successful, effec tive application. This application optimally in cludes a reproducible process involving a needs assessment, educational content planning, im plementation strategies, and appropriate evaluative methods. Familiarity with these concepts and tech niques will benefit the interested health care provider.

Treatment of peripheral neuropathies

There are three general approaches to treatment of peripheral neuropathy. First, an attempt should be made to reverse the pathophysiological process if its nature can be elucidated. Second, nerve metabolism can be stimulated and regeneration encouraged. Third, even if the neuropathy itself cannot be improved, symptomatic therapy can be employed. This review outlines the options available for each approach.