Large-fiber neuropathy in distal sensory neuropathy with normal routine nerve conduction

Whole plantar nerve conduction study: A new tool for early diagnosis of peripheral diabetic neuropathy

AIMS

Peripheral neuropathy (PN) affects two-thirds of type 2 diabetes patients (T2DM). According to diabetic PN length-dependent pattern, neurophysiological evaluation of foot-sole nerves might increase NCS diagnostic sensitivity, hence allowing early diagnosis of PN. Thus, we aim to assess the ability of whole plantar nerve (WPN) conduction in diabetic PN early diagnosis.

METHODS

This is a single center prospective observational cohort study on 70 T2DM patients referred to Internal Medicine Unit of A.O.U. "Luigi Vanvitelli" between October 2019/October 2020. Primary endpoint was WPN efficacy assessment in PN early detection. As secondary, we evaluated (i) a potential cut-off of SNAPs amplitude by WPN and (ii) WPN diagnostic accuracy vs. gold-standard distal sural nerve conduction.

RESULTS

ROC curve analysis allowed to establish two potential cut-offs for people aged ≤60 years (AUROC: 0.83, 95%CI: 0.69-0.96, p < 0.001) and ≤60 years (AUROC: 0.76, 95%CI: 0.59-0.93, p = 0.017). In depth, we fixed a cut-off of WPN-SNAP amplitude of 4.55 μV and 2.65 μV, respectively, with subsequent 48 patients classified as PN-T2DM.

CONCLUSIONS

Our data support WPN conduction study reliability in characterizing the most distal sensory nerve fibers at lower limbs. Thus, WPN may represent an extremely useful diagnostic tool for diabetic PN early detection.

Prevalence of denervation in the intrinsic foot muscles in patients with distal predominantly small fiber neuropathy

BACKGROUND

We aimed to evaluate the significance of electromyographic findings in the intrinsic foot muscles (IFMs) of patients with skin biopsy proven small fiber neuropathy (SFN).

METHODS

This was a single-center retrospective analysis of patients who underwent skin biopsy for intra-epidermal nerve fiber density (IENFD) measurement and electrodiagnostic (EDX) study for evaluation of polyneuropathy.

RESULTS

A total of 1416 patents with normal lower extremity EDX studies proximal to the foot were included. Active denervation was seen in 16.1% of IFMs in patients with skin biopsy proven SFN and 4.1% of patients without SFN (P < .0001). Reinnervation changes without active denervation were observed in 30.4% of SFN patients and 23.8% of patients without SFN (P = .01). IENFD was lower in SFN patients with active denervation in IFMs than without (P < .0001).

CONCLUSIONS

Evaluation of active denervation in the IFMs can reveal large fiber dysfunction in SFN patients with otherwise normal routine EDX findings.

Double-Shock Stimulation of the Superficial Radial Nerve Compared With Standard Medial Plantar Nerve Conduction in the Early Detection of Asymptomatic Diabetic Neuropathy: A Pilot Study

PURPOSE

Diabetes mellitus is a major public health problem. Diabetic polyneuropathy (DP) is one of the most common complications of diabetes mellitus. The early detection of DP is very important for timely treatment of symptoms and preventative foot care.

METHODS

Participants were sorted into 3 age- and sex-matched groups: 20 "healthy" individuals; 21 diabetic patients without DP symptoms, "asymptomatic"; and 24 diabetic patients suffering from symptoms consistent with DP, "symptomatic." All study participants had normal results on conventional nerve conduction studies. All groups underwent both medial plantar mixed nerve conduction (as a single-shock stimulation technique) and superficial radial nerve conduction (double-shock stimulation) measurements. Interstimulus intervals of 2 to 8 ms were used to record sensory nerve action potentials (SNAP) 1 and SNAP 2 for both stimuli.

RESULTS

We found statistically significant decreases in medial plantar NAPs' amplitude and conduction velocity, and SNAP1/SNAP2 ratios between the three groups, especially at smaller interstimulus intervals.

CONCLUSIONS

Both medial plantar mixed nerve conduction and double-shock superficial radial nerve stimulation are reliable methods for the early detection of asymptomatic DP. However, the medial plantar mixed nerve technique is easier and less time-consuming.

Nerve conduction study of the association between glycemic variability and diabetes neuropathy

BACKGROUND

It remains unclear whether glycemic variability is related to diabetes microvascular disease, especially diabetes peripheral neuropathy (DPN). We investigated the association between glycemic variability and DPN with type 1 or 2 diabetes.

METHODS

Forty patients (23 males and 17 females; aged 34-79 years) underwent continuous glucose monitoring (CGM) and a nerve conduction study (NCS). Glycemic variability was estimated by mean amplitude of glycemic excursions (MAGE) in CGM. DPN was quantitatively evaluated by NCS in the median, tibial, sural and medial plantar nerves.

RESULTS

MAGE had a significantly positive correlation with disease duration and low-density lipoprotein cholesterol level (r = 0.462, p = 0.003; and r = 0.40, p = 0.011, respectively), and a significantly negative correlation with BMI and medial plantar compound nerve action potential amplitude (r = - 0.39, p = 0.012; and r = - 0.32, p = 0.042, respectively). Multivariate linear regression analysis with adjustment for clinical background showed that MAGE (β = - 0.49, p= 0.007) was independently associated with a higher risk of medial plantar neuropathy.

CONCLUSIONS

Glycemic variability may be an independent risk factor for DPN.

Effects of anthropometric factors on nerve conduction: an electrophysiologic study of feet

BACKGROUND

Previous studies have shown that age, sex, and body mass index (BMI) affect the amplitude of sensory nerve action potentials (SNAPs), but the total effects of multiple factors and the most prominently affected nerves have not been elucidated. We systematically investigated the effects of these factors on motor and sensory nerves of the feet.

METHODS

The amplitude, latency, and conduction velocity of compound muscle action potential (CMAP), SNAP, and mixed nerve action potential (MNAP) of the posterior tibial, calcaneal, distal posterior tibial, medial and lateral plantar, and sural nerves were measured in 30 healthy individuals (60 feet). The effects of age, sex, height, and BMI on each nerve were estimated by correlation and linear regression analyses.

RESULTS

The amplitude of posterior tibial CMAP and distal posterior tibial MNAP decreased with BMI. The amplitude of medial plantar MNAP and sural SNAP decreased with height. The conduction velocity of calcaneal SNAP and distal posterior tibial and lateral plantar MNAP decreased with height and BMI. The conduction velocity of medial plantar MNAP decreased only with height. The latency of posterior tibial CMAP increased with age and height. The latency of lateral plantar CMAP and calcaneal SNAP increased with height. The latency of lateral plantar MNAP increased with BMI.

CONCLUSIONS

The effects of age, sex, height, and BMI in foot nerve conduction studies are not identical. Height and BMI were shown to strongly affect motor, sensory, and mixed nerve conduction. Further investigations are needed.

LOWER LIMB JOINT POSITION SENSE IN PATIENTS WITH TYPE II DIABETES MELLITUS

Diabetes mellitus (DM), of which type II has been described as an international epidemic, is a major cause of death. Diabetic peripheral neuropathy (PN) is a condition secondary to hyperglycemia, where progressive loss of peripheral nerve function, including sensory and motor functions, occurs over time. Early detection of PN-related impairments may be helpful for the management of patients with DM. Among the methods for the evaluation of these impairments, only that for joint position sense (JPS) requires both motor and sensory involvement. The purpose of the current study was to compare the JPS of the lower limb joints in patients with no or mild diabetic PN to those of normal controls both during weight-bearing (WB) and non-weight-bearing (NWB) conditions using 3D motion analysis methods. The results supported the hypothesis that in well controlled diabetic patients with no or mild PN, JPS deficits can be found only at the ankle joint during WB conditions, resulting in overestimation of dorsiflexion angles. This suggests that at the very early stage of development of diabetic PN, distal joint involvement precedes that of proximal joints. Early detection of these changes, through the assessment of the JPS for all the lower limb joints under both NWB and WB conditions, will be helpful for the development of clinical preventive and treatment programs for patients with DM, even if their glucose level are well controlled. Gait and balance training in these patients should emphasize proprioception training exercises during WB conditions.

Assessment of symptomatic diabetic patients with normal nerve conduction studies: utility of cutaneous silent periods and autonomic tests

Established electrophysiological methods have limited clinical utility in the diagnosis of small-fiber neuropathy (SFN). In this study, diabetic patients with clinically diagnosed SFN were evaluated with autonomic tests and cutaneous silent periods (CSPs). Thirty-one diabetic patients with clinically suspected SFN and normal nerve conduction studies were compared with 30 controls. In the upper extremities (UE), the CSP parameters did not differ statistically between the patient and control groups, whereas, in the lower extremities (LE), patients had prolonged CSP latencies (P = 0.018) and shortened CSP durations (P < 0.001). The sensitivity of the CSP duration was 32.6%, and the specificity was 96.7%. The expiration-to-inspiration ratios and amplitudes of the sympathetic skin responses in the lower extremities were also reduced. Our findings indicate that the diagnostic utility of CSPs was higher than that of the autonomic tests to support the clinically suspected diagnosis of SFN.

Comparison of sudomotor and sensory nerve testing in painful sensory neuropathies

OBJECTIVE

To compare results of quantitative sudomotor axon reflex testing (QSART), dorsal sural, and sural sensory nerve testing in patients with painful sensory neuropathy (PSN).

METHODS

Fifty-six patients with symptoms and neurologic examinations consistent with PSN who had both autonomic and nerve conduction studies were identified from 376 patients with a clinical diagnosis of painful neuropathy. Cases were clinically categorized as large-fiber or small-fiber neuropathies by described criteria. The results of sural, dorsal sural, and QSART tests were then analyzed in relationship to these two clinical groups.

RESULTS

Evidence of unmyelinated fiber abnormalities by QSART was noted in 85% of clinical large-fiber and 69% of clinical small-fiber groups. Dorsal sural potentials were absent in all the large-fiber group but also in 52% of clinically classified small-fiber neuropathies. When QSART and dorsal sural abnormalities were combined, the identification of abnormalities in all the cases of PSN was 89% with 75% of cases (42) showing mixed large and small fiber abnormalities, 14% unmyelinated sensory fiber abnormalities (by QSART), and 11% normal studies.

CONCLUSION

This study demonstrates the value of combining both QSART and dorsal sural sensory testing in verifying the diagnosis of PSN. The majority of cases demonstrate involvement of unmyelinated C fibers as well as large/medium myelinated fibers, thereby separating mixed large- and small-fiber sensory neuropathies from those cases classified by clinical criteria solely as small-fiber neuropathy.

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.

Medial plantar nerve conduction studies in healthy controls and diabetics

OBJECTIVE

To collect a reference material of the medial plantar nerve action potential, to test intra/interobserver reliability in healthy controls and to apply the test to a group of patients with diabetes mellitus.

METHODS

98 healthy controls and 50 patients with diabetes mellitus were included. The medial plantar nerve was stimulated orthodromically and recorded with a surface electrode. In the patient group, NCS of motor and sensory nerves and quantitative sensory testing were also performed.

RESULTS

Responses of the medial plantar nerve were obtained from all controls except from one aged 72. Amplitude decreased with age (r=-0.68, p<0.0001). Intra/interobserver reliability was acceptable. 52% of the patients had abnormal overall NCS classification. Forty-eight percent had delayed tibial F-response latency. The medial plantar NCS were abnormal in 59% of the cases (47% abnormal NAP amplitude and 39% reduced CV), 59% of those with abnormal NCS had symptoms of sensory polyneuropathy. Only 24% had abnormal sural amplitude. Cold perception threshold was abnormal in more patients (30%) than warmth perception threshold (14%).

CONCLUSIONS

Responses were easily obtained in controls under 70 years. In diabetics the amplitudes of the medial plantar nerve were abnormal more often than in the sural nerve.

SIGNIFICANCE

The medial plantar nerve response is reliable in patients under 70 years, and intra/interobserver reliability is acceptable.

Neuropathies of the foot

Compared with the common neuropathies affecting the hands (carpal tunnel syndrome and ulnar neuropathy), neuropathies of the feet have received less attention in the past. This is partly because of the rarity of these disorders as well as the lack of reliable electrophysiological tests for them. Over the years, nerve conduction tests for various nerves of the feet have been reported, and at this time techniques for all the nerves of the feet are available to the electromyographer. This review will provide up-to-date information on the current status of the research and issues relating to the neuropathies of the foot, with an emphasis on the most useful tests and the caveats for clinical neurophysiologists.

Simple and novel method to measure distal sensory nerve conduction of the medial plantar nerve

A simple and reliable method for recording sensory nerve action potentials (SNAPs) of the medial plantar nerve is described. Medial plantar SNAPs were recorded by placing surface electrodes on the sole. Ring electrodes were used for orthodromic stimulation at the big toe. Sixty-four healthy subjects ranging in age from 13 to 81 years were examined to establish normal values. Mean amplitude for the medial plantar SNAP was 4.7 +/- 2.8 microV and mean maximum conduction velocity was 43.5 +/- 6.4 m/s. The normal values for amplitude obtained for the medial plantar SNAPs were higher than those obtained by the method of Guiloff and Sherratt, and the sensitivity of our method for diagnosis of early sensory neuropathy was relatively higher. The method should therefore be useful in the diagnosis of early sensory neuropathy.

[Electrophysiological manifestations of chronic inflammatory demyelinating polyradiculoneuropathy]

There are four basic electrophysiological parameters of demyelination: reduced motor conduction velocity, prolonged distal motor latency and F waves, and motor conduction blocks. These parameters are combined to determine an electrophysiological set of criteria for chronic inflammatory demyelinating polyneuropathy (CIDP). Whereas their specificity is good, their sensitivity level does not exceed 75 percent. However, these sets of criteria are not commonly used especially in benign forms, at the beginning of the disease, in associated forms or in case of secondary axonal degeneration. We can push the limits using others criteria such as the terminal latency index, sensory criteria, or by the contribution of others electrophysiological procedures such as the radicular stimulation or sensory evoked potentials. Due to the therapeutic implications, any axonal neuropathy without aetiologia, with at least one demyelinating electrophysiological criteria, could be considered as a putative CIDP.

Small fibre neuropathies

PURPOSE OF REVIEW

To summarize the recent advances in aetiology, diagnostic assessment, and treatment of small fibre neuropathies.

RECENT FINDINGS

New causes of small fibre neuropathy have been recognized and advances in neurophysiologic and neuropathologic techniques for investigating small fibres have been made, increasing the interest in this field. In particular, skin biopsy proved to be a sensitive method to diagnose small fibre neuropathy. It allows the detection of subclinical abnormalities of peripheral nerve function in patients with diabetes and tongue denervation in patients with burning mouth syndrome. This technique has also been used to demonstrate the neuroprotective effect of erythropoietin in experimental models of neuropathy. Among nonconventional neurophysiologic techniques for investigating small fibres, laser-evoked potential and contact heat-evoked potential stimulators have been developed and deserve particular interest. Several trials on neuropathic pain that is a typical feature of small fibre neuropathies have been performed and guidelines have recently been published.

SUMMARY

Detection of small fibre impairment allows earlier diagnosis of neuropathy and could be used as an outcome measure in future regenerative neuropathy trials. Standardization of skin biopsy can have an important impact on clinical practice and research. Further studies are needed to assess the reliability of current neurophysiologic techniques for testing small fibre function in peripheral neuropathies and the correlation with well established neuropathologic examination.

Interdigital nerve conduction study of the foot for an early detection of diabetic sensory polyneuropathy

OBJECTIVE

To report on the value of interdigital nerve (IDN) conduction study (NCS) of the foot for the recognition of diabetic sensory polyneuropathy with normal routine NCS and the nature of electrophysiological abnormality in early diabetic sensory polyneuropathy.

METHODS

The sensory nerve conductions in the two digital and 4 IDNs of the foot were obtained orthodromically using the near-nerve needle and signal averaging technique.

RESULTS

In 21 patients with diabetic sensory polyneuropathy with normal routine NCS, a definite neuropathy pattern (abnormalities in more than 3 of 6 tested nerves) was observed in 12 patients (57.1%). The most common abnormalities that were found were a low amplitude in the sensory compound nerve action potential and an absent potential, indicating that early diabetic sensory polyneuropathy is due to axonal degeneration.

CONCLUSIONS

Interdigital NCS of the foot using near-nerve needle technique can identify neuropathy in diabetic sensory polyneuropathy with normal routine NCS. This technique offers a useful means of detecting nerve conduction abnormalities in the early stage of diabetic polyneuropathy.

The clinical identification of peripheral neuropathy among older persons

OBJECTIVE

To identify simple clinical rules for the detection of a diffuse peripheral neuropathy among older outpatients.

DESIGN

Observational, blinded, controlled study.

SETTING

A tertiary-care electrodiagnostic laboratory and biomechanics laboratory.

PARTICIPANTS

One hundred research subjects, 68 with electrodiagnostic evidence of peripheral neuropathy, between the ages of 50 and 80 years.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASUREMENTS

One examiner, unaware of the results of electrodiagnostic testing, evaluated Achilles' and patellar reflexes, Romberg testing, semiquantified vibration, and position sense at the toe and ankle in all subjects, and unipedal stance time and the Michigan Diabetes Neuropathy Score in a subset of subjects.

RESULTS

Significant group differences were present in all clinical measures tested. Three signs, Achilles' reflex (absent despite facilitation), vibration (128Hz tuning fork perceived for <10s), and position sense (<8/10 1-cm trials) at the toe, were the best predictors of peripheral neuropathy on both univariate and logistic regression (pseudo R(2)=.744) analyses. The presence of 2 or 3 signs versus 0 or 1 sign identified peripheral neuropathy with sensitivity, specificity, and positive and negative predictive values of 94.1%, 84.4%, 92.8%, and 87.1%, respectively. Values were similar among subgroups of subjects with and without diabetes mellitus. When other clinicians applied the technique to 12 more subjects, excellent interrater reliability regarding the presence of peripheral neuropathy (kappa=.833) and good to excellent interrater reliability for each sign (kappa range,.667-1.00) were shown.

CONCLUSION

Among older persons, the presence of 2 or 3 of the 3 clinical signs strongly suggested electrodiagnostic evidence of a peripheral neuropathy, regardless of etiology. Age-related decline in peripheral nerve function need not be a barrier to the clinical recognition of a diffuse peripheral neuropathy among older persons.

Nerve conduction studies in selected peripheral nerve disorders

PURPOSE OF REVIEW

The physiological properties of nerve and muscle are influenced by pathological changes and the aim of this review is to discuss recent contributions of electrophysiological studies to the understanding and diagnosis of selected peripheral nerve disorders. The relationships between pathology and physiology emphasize the close interdependence between electrophysiological studies, clinical deficits and other laboratory information. Attention should be paid to the strengths and limitations of electrophysiological methods, considering their impact on diagnosis and treatment of patients.

RECENT FINDINGS

Several studies have shown particular pathophysiological profiles associated with different antibody subtypes in autoimmune peripheral neuropathies and this association further supports the suggestion of pathological specificity in both acute and chronic neuropathy. The sensitivity and specificity of physiological profiles therefore become increasingly important since some of these neuropathies are accessible to treatment. On the other hand, the pathophysiological and clinical profiles may be heterogeneous in patients with some disorders. This could be related to a more indistinct division between different types of pathology with increased understanding of pathogenetic mechanisms. Moreover, new insights into disturbed axonal function have stimulated attempts to develop methods to explore normal and diseased human nerve function.

SUMMARY

The exploration of axonal membrane and ion-channel function has become accessible using studies of excitability and are of potential value where conventional studies only provide nonspecific evidence of the number of fibers and the integrity of myelin. These studies will presumably become increasingly important in the years ahead considering the lack of understanding of the functional disturbances in axonal neuropathies.

Class of nerve fiber involvement in sensory neuropathies: clinical characterization and utility of the plantar nerve action potential

Precise classification of distal sensory polyneuropathies (SN) according to fiber type involvement is desirable for clinical and research purposes. The sural sensory response has served as an electrophysiologic gold standard for the assessment of large-fiber sensory dysfunction. However, patients labeled as having small-fiber sensory neuropathies on the basis of a normal sural response frequently have clinical evidence of large-fiber dysfunction. The surface-recorded medial plantar potential has shown promise as a more sensitive indicator of large-fiber sensory dysfunction, but is not widely accepted because of concerns about age effects and a lack of large well-controlled studies in SN. We have thus correlated clinical type of SN: large-fiber sensory neuropathies (LFSN), small-fiber sensory neuropathies (SFSN), and mixed (large- and small-fiber) sensory neuropathies (MFSN) with sural and medial plantar nerve conduction studies in 133 consecutive patients with distal SN and 108 control subjects. A combination of stringent clinical characterization and electrophysiologic features, especially the surface-recorded medial plantar rather than sural potential, was complementary, and permitted a more clear separation of LFSN, MFSN, and SFSN than with either approach used alone.

Small-fiber neuropathy

Small-fiber neuropathy is a common disorder. It is often "idiopathic" and typically presents with painful feet in patients over the age of 60. Autoimmune mechanisms are often suspected, but rarely identified. Known causes of small-fiber neuropathy include diabetes mellitus, amyloidosis, toxins, and inherited sensory and autonomic neuropathies. Occasionally, small-fiber neuropathy is diffuse or multifocal. Depending on the type of small-fiber neuropathy, autonomic dysfunction can be significant or subclinical. Diagnosis is made on the basis of the clinical features, normal nerve conduction studies, and abnormal specialized tests of small-fiber function. These specialized studies include assessment of epidermal nerve fiber density as well as sudomotor, quantitative sensory, and cardiovagal testing. The sensitivities of these tests range from 59-88%. Each has certain advantages and disadvantages, and the tests may be complementary. Unless an underlying disease is identified, treatment is usually directed toward alleviation of neuropathic pain.

Ganglioside reactive antibodies in the neuropathy associated with celiac disease

We tested patients with celiac disease (CD) for the presence of serum anti-ganglioside antibodies. Six of twenty-seven patient sera were reactive against brain gangliosides by an agglutination immunoassay. Neurological examination in all six revealed the presence of distal sensory loss, consistent with the diagnosis of peripheral neuropathy. When tested by ELISA for antibodies to isolated GM1, GM2, GD1a, GD1b, GT1b, and GQ1b gangliosides, all six were positive for IgG antibodies to at least one. The neuropathy of celiac disease may be autoimmune and associated with anti-ganglioside antibodies. The presence of IgG reactivity furthermore implicates a T cell-mediated response to ganglioside antigens.