The relative diagnostic sensitivity of different F-wave parameters in various polyneuropathies

V, Manikandan M. Arm Length-Does It Influence Late Response in a Nerve Conduction Study?

Introduction  F wave response, a late response obtained from a motor nerve, can be influenced by various external factors like gender, temperature, height, weight, and limb length, and hence it causes variation in the measured parameters. Since very few studies have studied the impact of arm length on the F wave, this study was conducted to analyze the relation between the arm length on various parameters of F wave and hence to consider the importance of it during conduct of a nerve conduction study. Methods  The study was conducted among 40 healthy individuals and 40 diabetics with neuropathy. The arm length was measured in the upper limbs in both the groups and F wave was recorded following a conventional procedure using a standardized instrument. Results  This study showed that in the upper limbs of both the groups, there existed a positive correlation for certain parameters like minimum, maximum and mean latencies, persistence, FM latency and M latency, and a negative correlation for chronodispersion. Conclusion  F wave parameters should be adjusted for arm length to improve the sensitivity and diagnostic ability of neurological testing.

Vitamin D and diabetic peripheral neuropathy: A multi-centre nerve conduction study among Chinese patients with type 2 diabetes

AIMS

Increasing numbers of reports link vitamin D deficiency to diabetic peripheral neuropathy (DPN), yet evidence regarding neurological deficits and electromyogram is scarce. The present multi-centre study sought to investigate these associations based on objective quantifications.

MATERIALS AND METHODS

Information on DPN-related symptoms, signs, all diabetic microvascular complications, and nerve conduction abilities (quantified by nerve conduction amplitude and velocity, F-wave minimum latency (FML) of peripheral nerves) were collected from a derivation cohort of 1192 patients with type 2 diabetes (T2D). Correlation, regression analysis, and restricted cubic splines (RCS) were used to explore linear and non-linear relationships between vitamin D and DPN, which were validated in an external cohort of 223 patients.

RESULTS

Patients with DPN showed lower levels of vitamin D than those without DPN; patients with vitamin D deficiency (<30 nmol/L) tended to suffer more DPN-related neurological deficits (paraesthesia, prickling, abnormal temperature, ankle hyporeflexia, and distal pall hypoesthesia correlating with MNSI-exam score (Y = -0.005306X + 2.105, P = 0.048). Worse nerve conduction abilities (decreased motor nerve amplitude, sensory nerve amplitude, motor nerve velocity, and increased FML) were also observed in these patients. Vitamin D had a significant threshold association with DPN (adjusted OR = 4.136, P = 0.003; RCS P for non-linearity = 0.003) and correlates with other microvascular complications (diabetic retinopathy and diabetic nephropathy).

CONCLUSIONS

Vitamin D is associated with the conduction ability of peripheral nerves and may have a nerve- and threshold-selective relationship with the prevalence and severity of DPN among patients with T2D.

Determining the utility of minimum F-wave latency alterations in the electrodiagnosis of ulnar neuropathy at the elbow

BACKGROUND

Ulnar neuropathy at the elbow (UNE) is the second most common entrapment neuropathy. There is little information about the application of F-wave studies for evaluation of UNE.

OBJECTIVE

The aim of this study was to evaluate the diagnostic value of minimum F-wave (F-min) latency alterations by comparing this with nerve conduction analyses in UNE-suspected patients.

METHODS

Ninety-four UNE-suspected patients were admitted to this study. Sensory and motor nerve conduction and F-wave analyses on the median and ulnar nerves were performed on both upper extremities.

RESULTS

A total of 188 upper extremities of 94 patients were examined. Their mean age was 41.4±12.9 years, and 69 patients were female (73.4%). The mean ulnar-nerve across-elbow motor conduction velocity (MCV) in the affected arms was significantly slower than the velocity in healthy arms. The mean ulnar-nerve F-min latencies were significantly longer in the affected arms. Fifty-one patients were electrophysiologically diagnosed as presenting UNE (54.2%). Significantly slower mean ulnar-nerve across-elbow MCV, longer mean ulnar-nerve F-min latency and longer distal onset latency were detected in UNE-positive arms. Lastly, patients who were symptomatic but had normal nerve conduction were evaluated separately. Only the mean ulnar F-min latency was significantly longer in this group, compared with the healthy arms.

CONCLUSION

Our study confirmed the utility of F-min latency measurements in the electrodiagnosis of UNE. F-wave latency differences can help in making an early diagnosis to provide better treatment options.

Establishing Normal Values for F-Wave Latencies in Diagnosing Peripheral Neuropathies for the Pediatric Population

PURPOSE

We present a unique technique applying F-wave latencies to assist in the diagnosis of peripheral neuropathy within the pediatric age group.

METHODS

We calculated an F-wave estimated deviance adjusted for limb length measurements, distal motor conduction velocity, and distal motor latencies. We compared the F-wave estimated deviance from the normal subjects with those with peripheral neuropathy (both axonal and demyelinating) to establish diagnostic accuracy in pediatric patients.

RESULTS

The normal range for the F-wave estimated deviance in the upper limb was -1 to +6 ms and in the lower limb was -8 to +5 ms. When compared with 82 subjects with peripheral neuropathy, there was a significant difference between the normal subjects and those with neuropathy (P values between 0.002 and 0.0005 for each of the individual nerves tested).

CONCLUSIONS

The F-wave estimated deviance is independent of age and can be accurately applied to the electrodiagnostic testing of pediatric patients with suspected neuropathy.

Acute lumbar polyradiculoneuropathy as early sign of methotrexate intrathecal neurotoxicity: Case report and literature review

Acute paraplegia after treatment with intrathecal methotrexate requires a complete spinal cord neuroimaging as well as electrodiagnostic examination. The absence of lumbosacral F waves motor responses without demyelinating findings may indicate early direct root toxicity. Early electromyography (EMG) screening could be a valuable tool for detecting peripheral neurotoxicity.

F wave index: A diagnostic tool for peripheral neuropathy

Background & objectives:

Each skeletal muscle is usually supplied by two or more nerve roots and if one nerve root is affected and the other is spared, the clinically used F wave minimum latency can still be normal. An F wave index was constructed taking into consideration the other parameters of the F wave such as persistence, chronodispersion, latency, arm-length to determine its usefulness in the diagnosis of peripheral neuropathy. This study was undertaken to construct the F wave index in the upper limb for the median nerve in normal healthy adult males and in patients with peripheral neuropathy and to compare the values obtained in both groups.

Methods:

This hospital-based study was carried out on 40 males who were diagnosed to have peripheral neuropathy and on 40 age matched healthy males who served as the control group. The F wave recording was done using a digitalized nerve conduction/electromyography/EP machine in a quiet and dimly lit room. All recordings were done between 0900 and 1100 h at an ambient temperature of 22°C. The F wave recording was obtained from a fully relaxed muscle by stimulating the median nerve.

Results:

The median value for F wave index obtained from median nerve (abductor pollicis brevis) in patients with peripheral neuropathy [right arm - 35.85, interquartile range (IQR) - 35.26; left arm - 39.49, IQR - 39.49] was significantly lower (P=0.001) as compared to the control group (right arm - 102.62, IQR - 83.76; left arm - 77.43, IQR - 58.02).

Interpretation & conclusions:

Our results showed that F wave index in upper limb was significantly lower in patients with peripheral neuropathy than the healthy controls, and could be used for early detection of peripheral neuropathy.

Generation of Repeater F Waves in Healthy Subjects

PURPOSE

F waves identical in latency, size, and shape, known as repeater F waves, have been observed occasionally in normal motor conduction recordings. The purpose of this study was to examine the occurrence and characteristics of repeater F waves in healthy subjects under different testing conditions, aiming to selectively excite lower and higher threshold motor fibers.

METHODS

Sessions of 40 traces were recorded from the ulnar nerve in 12 volunteers, applying/using supramaximal, submaximal stimuli (intensity able to elicit 30% and 60% of the maximum compound muscle action potential amplitude), and a collision technique. Repeater F waves were identified and their numbers and relative frequency were estimated. For this purpose, a custom-designed software program was developed, to avoid misjudgments of simple visual inspection.

RESULTS

Repeater occurrence was significantly higher using 30% submaximal intensity compared with the standard supramaximal stimulation. There was an inverse significant association between repeater index and overall F wave quantity. Repeaters' latency, amplitude, and duration measurements were within the ranges of the nonrepeaters.

CONCLUSIONS

We herein showed that in healthy subjects the presence of repeater F waves might increase, when stimulation conditions other than standard single, supramaximal impulses were used. The frequency of repeaters was dependent on the overall F wave persistence, but there was no evidence to support a relationship with the type of motoneurons that was preferentially stimulated.

Recurrence Quantification Analysis of F-Waves and the Evaluation of Neuropathies

Electrodiagnostic (EDX) patterns of neuropathic dysfunction have been based on axonal/demyelinating criteria requiring prior assumptions. This has not produced classifications of desired sensitivity or specificity. Furthermore, standard nerve conduction studies have limited reproducibility. New methodologies in EDX seem important. Recurrent Quantification Analysis (RQA) is a nonlinear method for examining patterns of recurrence. RQA might provide a unique method for the EDX evaluation of neuropathies. RQA was used to analyze F-wave recordings from the abductor hallucis muscle in 61 patients with neuropathies. Twenty-nine of these patients had diabetes as the sole cause of their neuropathies. In the other 32 patients, the etiologies of the neuropathies were diverse. Commonly used EDX variables were also recorded. RQA data could separate the 29 patients with diabetic neuropathies from the other 32 patients (P < 0.009). Statistically significant differences in two EDX variables were also present: compound muscle action potential amplitudes (P < 0.007) and F-wave persistence (P < 0.001). RQA analysis of F-waves seemed able to distinguish diabetic neuropathies from the other neuropathies studied, and this separation was associated with specific physiological abnormalities. This study would therefore support the idea that RQA of F-waves can distinguish between types of neuropathic dysfunction based on EDX data alone without prior assumptions.

Prolongation of F-wave minimal latency: a sensitive predictor of polyneuropathy

INTRODUCTION

To evaluate the sensitivity of F-wave minimal latencies, we compared F-waves with motor and sensory nerve conduction studies (MNCS and SNCS) in patients with peripheral neuropathy.

METHODS

A retrospective chart review conducted in 484 patients confirmed the clinical evidence of a polyneuropathy, and studies of F-wave minimal latencies as well as MNCS and SNCS in each patient.

RESULTS

Overall rate of abnormality reached 469/484 (96.9%) for F-wave minimal latencies as compared to 374/484 (77%) for nerve conduction studies ( p < 0.0001). Nerve-specific abnormalities of F-waves showed 290/354 (82%), 140/171 (82%), 367/398 (92%) and 357/376 (95%) for median, ulnar, peroneal and tibial nerves, respectively. Corresponding values for MNCS consisted of 108/354 (31%), 29/171 (17%), 258/398 (65%) and 189/376 (50%) (all p < 0.0001). In contrast, SNCS revealed abnormalities in 120/333 (36%), 60/159 (38%) and 266/474 (56%) of median, ulnar and sural nerves.

CONCLUSION

F-wave minimal latencies serve as the best predictor of polyneuropathy followed by SNCS and then MNCS.

Cauda equina conduction time in Guillain-Barré syndrome

The proximal segment of peripheral nerves is assumed to be involved in both demyelinating and axonal types of Guillain-Barré syndrome (GBS). However, electrophysiological examinations have not yet clarified if this segment is involved. We measured cauda equina conduction time (CECT) in nine demyelinating GBS and seven axonal GBS patients. Compound muscle action potentials (CMAPs) were recorded from the abductor hallucis muscle. Electrical stimulation was given at the ankle and the knee, and magnetic stimulation was given over the first sacral (S1) and first lumbar (L1) spinous processes using a magnetic augmented translumbosacral stimulation (MATS) coil. CECT was obtained by subtracting S1-level latency from L1-level latency. CECT was prolonged in all the patients with demyelinating GBS who had leg symptoms, whereas motor conduction velocity (MCV) at the peripheral nerve trunk was normal in all the patients. In all the patients with axonal GBS having leg symptoms, CECT and MCV were normal and no conduction blocks were detected between the ankle and the neuro-foramina. The cauda equina is much more frequently involved than the peripheral nerve trunk in demyelinating GBS. In axonal GBS, usually, CECT is normal and segmental lesions are absent between the ankle and the neuro-foramina. Therefore, the CECT measurement should be very useful for directly detecting demyelinating lesions in GBS.

Establishment of a method to measure length of the ulnar nerve and standardize F-wave values in clinically normal beagles

We designed a new method of measuring the length of the ulnar nerve and determining standard values for F-wave parameters of the ulnar nerve in clinically normal beagles. Nerve length must be precisely measured to determine F-wave latency and conduction velocity. The length of the forelimb has served as the length of the ulnar nerve for F-wave assessments, but report indicates that F-wave latency is proportional to the length of the pathway traveled by nerve impulses. Therefore, we measured the surface distance from a stimulus point to the spinous process of the first thoracic vertebra (nerve length 1) and the anterior horn of the scapula (nerve length 2) as landmarks through the olecranon and the shoulder blade acromion. The correlation coefficients between the shortest F-wave latency and the length of nerves 1, 2 or the forelimb were 0.61, 0.7 and 0.58. Nerve length 2 generated the highest value. Furthermore, the anterior horn of the scapula was easily palpated in any dog regardless of well-fed body. We concluded that nerve length 2 was optimal for measuring the length of the ulnar nerve.

Cutaneous silent period recordings in demyelinating and axonal polyneuropathies

OBJECTIVE

To investigate the cutaneous silent period (CSP), a spinal inhibitory reflex mainly mediated by A-delta fibres, in demyelinating and axonal polyneuropathy (PNP) and evaluate whether CSP parameters differ between patients with and without neuropathic pain.

METHODS

Eighty-four patients with demyelinating PNP, 178 patients with axonal PNP and 265 controls underwent clinical examination, DN4 questionnaire, standard nerve conduction study, motor-root stimulation and CSP recordings from abductor digiti minimi. We calculated the afferent conduction time of CSP (a-CSP time) with the formula: CSP latency-root motor evoked potential latency.

RESULTS

In the demyelinating PNP group the a-CSP time was significantly longer; in the axonal PNP group, CSP duration was shorter than the demyelinating group (p=0.010) and controls (p=0.001). CSP parameters were not different between patients with and without neuropathic pain.

CONCLUSIONS

The abnormality of a-CSP time in the demyelinating PNP group suggests the crucial role of A-delta fibres in the mechanism of CSP; the shorter CSP duration in the axonal PNP group supports the strong influence of the number of axons on this parameter. Our study suggests that neuropathic pain could be related to pathophysiological mechanisms differing from mere A-delta fibre loss.

SIGNIFICANCE

CSP evaluation is effective in detecting A-delta fibre dysfunction in axonal as well as demyelinating PNP.

Effects of colistin on the sensory nerve conduction velocity and F-wave in mice

The aim of this study was to examine the changes of sensory nerve conduction velocity (SNCV) and F-wave for colistin-induced peripheral neurotoxicity using a mouse model. Mice were administered with colistin 5, 7.5 and 15 mg/kg/day via a 3-min. intravenous infusion. The sensory nerve conduction velocity (SNCV) and F-wave were measured using the bipolar recording electrodes. The SNCV and F-wave latency changed in a dose- and time-dependent manner. The significant increase of F-wave latency and significant decrease of SNCV appeared on day 3 (p < 0.05 and 0.01, respectively) in the 15 mg/kg/day group, and they were markedly changed on day 7 in the 7.5 mg/kg/day (p < 0.01 and 0.05, respectively) and 15 mg/kg/day groups (both p < 0.01). In addition, F-wave latency also significantly increased on day 7 in the 5 mg/kg/day group (p < 0.05) without any clinical signs. These results indicate that SNCV and F-wave latency were more sensitive in colistin-induced neurotoxicity in mice, which highlights the early monitoring tool of polymyxins neurotoxicity in the clinic.

The comparison of multiple F-wave variable studies and magnetic resonance imaging examinations in the assessment of cervical radiculopathy

OBJECTIVE

The aims of this study were to investigate the correlation of the findings of multiple median and ulnar F-wave variables and magnetic resonance imaging examinations in the prediction of cervical radiculopathy.

DESIGN

The data of 68 patients who underwent both nerve conduction studies of the upper extremities and cervical spine magnetic resonance imaging within 3 mos of the nerve conduction studies were retrospectively reviewed and reinterpreted. The associations between multiple median and ulnar F-wave variables (including persistence, chronodispersion, and minimal, maximal, and mean latencies) and magnetic resonance imaging evidence of lower cervical spondylotic radiculopathy (i.e., C7, C8, and T1 radiculopathy) were investigated.

RESULTS

Patients with lower cervical radiculopathy exhibited reduced right median F-wave persistence (P = 0.011), increased right ulnar F-wave chronodispersion (P = 0.041), and a trend toward increased left ulnar F-wave chronodispersion (P = 0.059); however, there were no other consistent significant differences in the F-wave variables between patients with and patients without magnetic resonance imaging evidence of lower cervical radiculopathy. In comparison with normal reference values established previously, the sensitivity and positive predictive value of F-wave variable abnormalities for predicting lower cervical radiculopathy were low.

CONCLUSIONS

There was a low correlation between F-wave studies and magnetic resonance imaging examinations. The diagnostic utility of multiple F-wave variables in the prediction of cervical radiculopathy was not supported by this study.

Multifocal acquired sensory and motor neuropathy: electrodiagnostic features

The electrodiagnostic studies of 13 consecutive patients with multifocal sensory and motor neuropathy of unknown etiology were reviewed to determine whether they exhibit features of demyelination or axonal degeneration. The type and frequency of demyelinating features, fulfillment of electrodiagnostic criteria for chronic inflammatory demyelinating polyneuropathy (CIDP), and response to immunotherapy were noted. Of 13 patients, 11 had at least one electrodiagnostic feature of demyelination at presentation and 2 had none. Seventeen percent to 77% of the patients fulfilled at least one of the published electrodiagnostic CIDP criteria, depending on the criteria used, but the number of demyelinating features per patient was less than reported for unselected patients with CIDP. Patients with multifocal sensory and motor neuropathy had a similar percentage of nerves with partial conduction block or F-wave prolongation as reported for unselected CIDP, but a smaller percentage of nerves exhibiting prolonged distal compound muscle action potential duration, distal latency prolongation or slowed conduction velocities. All treated patients, including 2 who did not meet any CIDP criteria, had at least a moderate response to immunotherapy. The results indicate that a large majority of, but not all, patients with idiopathic multifocal sensory and motor neuropathies exhibit electrodiagnostic features of demyelination, although fewer than seen in classic CIDP.

Practical electrodiagnostic value of F-wave studies in chronic inflammatory demyelinating polyneuropathy

OBJECTIVES

To ascertain the practical electrodiagnostic value of F-waves in chronic inflammatory demyelinating polyneuropathy (CIDP).

METHODS

We evaluated the diagnostic utility of F-waves in 18 prospectively-recruited patients with typical CIDP. Minimum/maximum/mean F-wave latencies, F-wave chronodispersion and F-wave persistence, were determined in median/ulnar/fibular/tibial nerves in patients and compared to controls with axonal neuropathy.

RESULTS

All latencies were significantly more delayed in CIDP patients. F-wave chronodispersion was significantly greater in median and ulnar nerves and F-wave persistence significantly more reduced in tibial nerves in CIDP patients. Use of these supplementary F-wave parameters was of value in identifying CIDP nerves. However F-wave studies were only of additional benefit to other demyelinating parameters in about 15% of all studied CIDP nerves.

CONCLUSIONS

F-waves may be diagnostically helpful in CIDP in a minority of nerves without other nerve conduction abnormalities. Analysis of F-wave chronodispersion in upper limb nerves and possibly of F-wave persistence in tibial nerves, may add value to basic minimum F-wave latency studies.

SIGNIFICANCE

These results suggest F-wave analysis may not need to be systematic, for all nerves, in patients with suspected CIDP, especially those intolerant to electrical stimulation. Chronodispersion and persistence may be helpful parameters to consider in addition to minimum latency.

F wave to height or limb length ratios as rational alternatives for F wave latency in clinical electrodiagnostic medicine

OBJECTIVE

To delineate the F wave latency/height (F min/He) or F wave latency/limb length (F min/L) ratio as a more useful alternative for the currently reported shortest latency in milliseconds.

METHODS

One hundred and sixty-six healthy volunteers, 85 upper limbs and 84 lower limbs entered the study. Minimum F wave latencies were determined in median, ulnar, tibial and peroneal nerves. The F min/He and F min/L ratios of each nerve were calculated.

RESULTS

F latencies of all nerves had significant correlation with height and limb length but there was no correlation between either F min/He or F min/L and height in any nerve except for peroneal F min/He (p = 0.04, r = 0.23).

CONCLUSIONS

Using the F min/He or F min/L ratios are more accurate than reporting only the F wave minimum latency, since these ratios incorporate corrections for height and/or limb length. This method also eliminates the false positive and negative reports caused by using a single reference table for all heights.

SIGNIFICANCE

A unique reference table can be produced using the F min/He or F min/L for all populations and races, so that the comparison between different population samples can be done easily. Also data of different investigations can be pooled together for meta-analysis purposes when a single reference table is used for different samples.

Acute motor response following a single IVIG treatment course in chronic inflammatory demyelinating polyneuropathy

In chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), the acute motor response following withdrawal and reestablishment of intravenous immunoglobulin (IVIG) therapy was studied. In a prospectively designed case series 11 CIDP patients in IVIG maintenance therapy were assessed with isokinetic dynamometry, nerve conduction studies, and functional tests. After short-term withdrawal of IVIG, eight treatment-responsive patients had a 14.2% (8.6-20.0) loss of isokinetic strength of 12 muscle groups. Three patients remained stable without treatment and were excluded from further study. On days 5 and 10 after reinitiation of IVIG therapy isokinetic muscle strength increased by 5.5% (1.6-9.6) and 11.9% (7.5-16.5), respectively, but there was no further increase at day 15. Improvement of walking velocity and hand function coincided. The minimal F-wave latency shortened, whereas other electrophysiological parameters remained unchanged. In conclusion, isokinetic dynamometry is a sensitive and clinically relevant method for monitoring the acute response to IVIG treatment in CIDP.

F-wave conduction velocity, persistence, and amplitude for the tibial nerve in clinically normal cats

OBJECTIVE

To establish a method of F-wave evaluation and to determine normative values of F-wave parameters, including F-wave conduction velocity, persistence, and amplitude for the tibial nerve in cats.

ANIMALS

30 clinically normal cats.

PROCEDURES

F-waves elicited in the interosseous muscles by stimulation of the tibial nerve were recorded, and linear regression analyses of the shortest latency versus the length of the tibial nerve and the limb length were performed. F-wave persistence was calculated by dividing the number of recorded F-waves by the number of stimuli.

RESULTS

The correlation coefficient between F-wave latency and nerve length was 0.92, and that between F-wave latency and limb length was 0.58. Mean +/- SD F-wave conduction velocity of the tibial nerve was calculated to be 97.1 +/- 5.0 m/s. Linear regression analysis yielded the regression equation as follows: F-wave latency (milliseconds) = 2.60 + (0.02 x nerve length [mm]). Mean F-wave persistence and amplitude were 98.7 +/- 2.3% and 1.01 +/- 0.62 mV, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that nerve length should be used for nerve conduction studies of F-waves in felids. The regression equation for F-wave latency, conduction velocity, persistence, and amplitude may contribute to the diagnosis of nervous system diseases or injury in cats, such as trauma to the spinal cord or diabetic neuropathy.

Polyneuropathy in hemodialysis patients: The most sensitive electrophysiological parameters and dialysis adequacy

BACKGROUND

Polyneuropathy (PNP) is a common complication in hemodialysis (HD) patients. Electrophysiological parameters are quantitative indices of its severity. The aim of our study was to find the prevalence of pathologic electrophysiological parameters, to assess their prevalence in relation to duration of HD treatment and age, to establish which parameters are the most sensitive in demonstrating PNP and to find an association between them and HD adequacy.

PATIENTS AND METHODS

We included 84 (50 men, 34 women) HD patients (average age 47.32 years; average dialysis duration 62.56 months) and divided them into three groups according to the duration of HD treatment. Each group was further divided into two subgroups according to age. We included electrophysiological parameters for evaluation of motor and sensory nerve functions (Medelec Sapphire Premiere device). HD adequacy was measured with urea kinetic modeling (Kt/V).

RESULTS

PNP was found in 77 (91.6%) HD patients and was more common in men (P < 0.016). The association between the number of pathologic electrophysiological parameters and age (P < 0.0001), duration of HD treatment (P < 0.009) and HD adequacy (P < 0.0001) was statistically significant. The most sensitive electrophysiological parameter was the latency of the F wave (pathologic values of F wave latency in the lower limbs in 86% patients and in the upper limbs in 49%). Sensory conduction velocities and the amplitudes of the orthodromic sensory action potentials and the M wave were also sensitive parameters. The F wave latency of different nerves was associated with dialysis adequacy.

CONCLUSIONS

PNP is frequent in HD patients and is associated with age and duration of dialysis treatment. The most sensitive electrophysiological parameter of PNP is F wave latency, which may also be used as a parameter of dialysis adequacy.

F-waves: neurophysiology and clinical value

This review deals with F responses, which are late responses obtained by supramaximal stimulation of virtually all the motor and mixed peripheral nerves. They are recorded over a muscle innervated by the stimulated nerve. The first description of F-waves was published in the fifties. Their neurophysiological mechanisms have been abundantly discussed in the literature leading to a current consensus, whereby F-waves are considered as antidromic responses produced by a pool of motoneurons activated by peripheral nerve stimulation. In the first part of this review, the neurophysiological mechanisms of F-waves as well as the distinction between these and H reflexes are described from a historical point of view. Other late responses are intentionally not reported; nevertheless A-waves are discussed since they are frequently ill-described in a number of conditions. Stimulation and recording procedures as well as F-wave parameters analysis are detailed, with emphasis on measures most useful for clinical purposes. A rigorous F-wave recording method is mandatory for reliable and meaningful analyses. Physiological factors, which influence F-waves such as ageing, drugs and sleep, must be known and their effects discussed. Also, as maturation is an important factor in clinical neurophysiology, data on F-wave ontogenesis are reviewed and discussed. Finally, the different F-wave alterations described so far in the literature, in either peripheral or central disorders, are listed and commented. It is emphasised that F-waves are particularly useful for the diagnosis of polyneuropathies at a very early stage and for the diagnosis of proximal nerve lesions. F-wave recording is indeed one of the rare methods in routine examination allowing at the same time the functional assessment of motor fibres on their proximal segment, and contributing to the evaluation of motoneuronal excitability.

Various aspects of F-wave values in a healthy population

OBJECTIVE

To characterize various aspects of F-wave in a healthy population and establish normative data for future clinical use.

METHODS

A total of 100 healthy volunteers underwent sensory and motor nerve conduction studies of the ulnar and tibial nerves, including F waves elicited by 32 stimuli.

RESULTS

The F-wave measurements (mean +/- SD for ulnar vs tibial nerve) consisted of persistence (83 +/- 19 vs 97 +/- 5%), minimum, mean and maximum latencies (26.5 +/- 2.1, 28.1 +/- 2.2, and 30.4 +/- 2.3 vs 47.0 +/- 4.1, 49.6 +/- 4.4, and 52.5 +/- 4.4 ms), minimum, mean and maximum F-wave conduction velocities (FWCV) (55.0 +/- 2.7, 60.0 +/- 2.3, and 64.0 +/- 3.0 vs 49.0 +/- 2.9, 52.2 +/- 3.1, and 55.5 +/- 3.4 m/s), chronodispersion (3.9 +/- 0.9 vs 5.5 +/- 1.4 ms), mean amplitude (347 +/- 152 vs 384 +/- 148 microV) and mean duration (8.6 +/- 2.9 vs 13.0 +/- 4.5 ms). Additional measures, registered by electronic averaging, included latency (27.4 +/- 2.3 vs 48.6 +/- 4.7 ms), duration (9.6 +/- 2.2 vs 16.4 +/- 4.2 ms), and amplitude (299 +/- 156 vs 208 +/- 116 microV).

CONCLUSIONS

The use of a height nomogram serves well as an acceptable means to adjust F latencies for the limb length. In addition to the commonly used minimal latency, maximal FWCV, and persistence, clinically relevant measures with a narrow variability includes mean and maximal latencies, chronodispersion, and mean duration. In particular, mean latency obtained with 10 stimuli gave accurate results either for group or individual analysis.

SIGNIFICANCE

The data help establish an adequate manner of recording F-wave latencies in clinical evaluation.

[Diagnostic value of the F-reaction in localization of the level of peripheral motor neuron lesions]

F-wave is a secondary muscle response, which occurs by antidromic activation of the limited number of alphamotoneurons. Based on M- and F-response and the nerve length, the conduction time, conduction velocity, and the ratio of F-response can be determined. These parameters help in assessing the data about functional condition of peripheral motor neurons along the most proximal segment in relatively simple and non-invasive way. In routine practical work, minimal latency of F-wave is measured, while F-wave conduction time, F-wave conduction velocity and F-ratio are not measured. The aim of this research was to examine the importance of F-wave latency, F-wave conduction time, F-wave conduction velocity, and F-ratio in the localization of level of lesion of peripheral motor neurons. Electromyoneurography examination included 50 patients with radiculopathies of lumbosacral part of spinal cord, 50 patients with neuropathy, and 25 healthy persons. Minimal latency of F-wave for tibial nerve and peroneal nerve was determined after 10 stimulations. F-wave latency, F-wave conduction time, F-wave conduction velocity, and F-ratio were determined in accordance with the formulas defined by Kimura. The results of our test have shown that F-wave latency, F wave conduction time, F-wave conduction velocity, were important electrophysiological parameters, while F-ratio was found to be highly sensitive, which made it the most valid electro-physiological parameter in the differentiation of proximal and distal lesion of peripheral motor neuron.

Reference values of F wave parameters in healthy subjects

OBJECTIVE AND METHODS

A large reference value database for F wave parameters was constructed with data from 121 to 196 healthy subjects; the age range of the subjects was 14-95 years. We studied the following parameters: minimum F wave latency (FMINLAT), mean F wave latency (FMEANLAT), maximum F wave latency (FMAXLAT), number of F waves/20 stimuli (FNUMBER) and F wave dispersion (FDISP=FMAXLAT-FMINLAT). The median, ulnar, peroneal and tibial nerves were studied.

RESULTS

Height explains almost half of the FMINLAT variability. The F wave latency increases with height in the arms by 0.2 ms/cm and in legs 0.4 ms/cm. The effect of age on F wave latency in the arms is relatively small, only 0.03 ms/year; and in the legs age increases the FMINLAT by 0.1 ms/year. Gender does not affect FMINLAT in a systematic way. The peroneal nerve has slightly longer FMINLAT than the tibial nerve, while the FNUMBER is higher in the tibial nerve than the peroneal nerve. The differences between the ulnar and median nerve are slight. There is a very high correlation between all 3 latency parameters (FMINLAT, FMAXLAT and FMEANLAT), but no correlation between FDISP and FNUMBER and the other parameters. Side to side comparisons reveals no significant differences in any of the parameters except for the median nerve FMINLAT and FMEANLAT, which is 0.2 ms longer on the right than left. If side difference of more than 2 standard deviation is taken as the upper limit for normal, the side difference in arms is 1.4 ms and in legs 3 ms. In repeated studies the interexaminer variability is small; the correlation coefficient between the different F parameters is high (P>0.6 in arms and P>0.7 in legs). In the arms the upper limit for a significant difference of FMINLAT on repeated studies in the median nerve is 1.0 and 1.7 ms for the ulnar nerve. In the legs, FMINLAT for the peroneal nerve is 2.6 ms and for the tibial nerve is 2.1 ms.

CONCLUSIONS

This large reference value database can be used not only to evaluate single measurements in relation with height and age, but also to compare right and left side and changes over time at repeated studies.

Electrodiagnostic approach to patients with weakness

Electrodiagnosis has a key role in the evaluation of patients presenting with weakness. The electrodiagnostician should maintain a broad inclusive differential diagnosis and tailor the examination using a sound conceptual framework. A clear understanding of what is normal provides the proper foundation upon which to judge electrodiagnostic findings. Many peripheral neuromuscular conditions manifest themselves in characteristic ways on NEE and nerve conduction testing, making them identifiable to the skilled electrodiagnostic medicine consultant.

Detection of lumbosacral nerve root compression with a novel composite nerve conduction measurement

STUDY DESIGN

Multivariate logistic regression techniques were used to develop a composite nerve conduction measurement that detects lumbosacral (L5, S1, or both) nerve root compression.

OBJECTIVES

To evaluate the diagnostic efficacy of a composite nerve conduction measurement for detection of lumbosacral nerve root compression.

SUMMARY OF BACKGROUND DATA

Nerve root involvement is characterized by clinical abnormalities and confirmed by radiologic and electrodiagnostic studies. Imaging studies visualize structural abnormalities; however, they are associated with high false-positive rates. Electrodiagnostic methods assess the physiologic integrity of the nerve roots. One form of electrodiagnostic testing, nerve conduction studies, is widely used for evaluation of musculoskeletal and neuromuscular complaints. Although similar clinical value is expected for the evaluation of nerve root compromise, prior applications of nerve conduction studies have yielded widely varying results.

METHODS

Two groups of subjects were compared. The L5-S1 compression group was composed of 25 patients with magnetic resonance imaging-confirmed lumbosacral (L5, S1, or both) nerve root compression and symptoms in the appropriate segmental distribution. The majority of subjects (22) had at least one of the following findings on physical examination: positive straight-leg raise test, diminished ankle reflexes, sensory loss, or weakness. The control group consisted of 35 asymptomatic individuals with no history of radiculopathy or potentially confounding neuropathology. The posterior tibial and deep peroneal nerves were evaluated bilaterally in all study subjects using standard nerve conduction procedures, which consisted of the measurement of distal motor latencies and F-wave latencies that assess nerve root pathophysiology. A composite nerve conduction measurement was determined using multivariate logistic regression analysis. The efficacy of the composite measurement was assessed by receiver operating characteristic curve analysis and by the diagnostic sensitivity and specificity.

RESULTS

Five F-wave latency parameters (peroneal mean F-wave latency, odds ratio = 0.42; peroneal seventh F-wave latency decile, odds ratio = 2.71; tibial mean F-wave latency, odds ratio = 8.90; tibial first F-wave latency decile, odds ratio = 0.47; tibial maximum F-wave latency, odds ratio = 0.44) were found to be predictive of nerve root compression. A composite nerve conduction measurement, NC composite, constructed from these five parameters (NC composite = exp(phi)/(1 + exp(phi)), phi = -31.2 + 1.0 * Per7 Decile - 0.88 * PerMean + 2.2 * TibMean - 0.88 * Tib1 Decile - 0.83 * TibMax) yielded an area under the receiver operating characteristic curve of 0.91. At a threshold of 0.20, NC composite had a diagnostic specificity of 84.3% and a sensitivity of 83.3%.

CONCLUSION

This preliminary study suggests that a novel composite nerve conduction measurement, based on F-wave latency parameters, may be highly effective at detecting magnetic resonance imaging-confirmed lumbosacral nerve root compression. Because these measurements provide objective evidence of functional nerve root compromise and are noninvasive, they may be of diagnostic value to clinicians evaluating patients presenting with low back and leg pain.

Axonal neuropathy in chronic peripheral arterial occlusive disease

Chronic peripheral arterial occlusive disease of the lower limbs may cause tissue damage. Type and extent of peripheral nerve involvement is controversial. We examined 25 patients with peripheral arterial occlusive disease in various grades of severity and 37 age-matched healthy controls using conventional angiography and motor and sensory nerve conduction tests. Subjects with confounding factors for peripheral neuropathies were excluded. We found prolongation of distal motor latencies, decrease of motor and sensory nerve conduction velocities, and reduction in amplitude of the compound muscle action potential. Amplitudes of the compound muscle action potentials were lower in patients with pain at rest than in patients with intermittent claudication and decreased with increasing neurological disability score. Sural nerve conduction velocity, peroneal nerve F-wave chronodispersion, and tibial nerve F-wave persistence were the most frequent abnormal findings. Therefore we concluded that chronic peripheral arterial occlusive disease causes axonal degeneration, resulting in axonal polyneuropathy.

Neurography: late responses

The meaningfulness of routine conduction velocity studies can be increased when so-called late responses (F waves, H reflex, and intermediate late responses) are considered. The techniques to elicit different types of late responses are described as well as their occurrence in physiological and pathological conditions. Late responses are muscle action potentials of different origins and different configurations, and they have different clinical implications. F waves are recurrent discharges of alpha-motor neurons that have diagnostic value in patients with demyelinating neuropathies and proximal lesions of peripheral nerves. H reflexes are similar to the muscle stretch reflex. H reflexes can be elicited in only a few nerves, so they are routinely used only in patients suffering from sacral plexopathies, S1 radiculopathy, and polyneuropathies. Intermediate late discharges are of various origins and clinical significance. True axon reflexes occur seldom in routine neurography and are usually caused by submaximal stimulation. However, A waves with a constant shape, latency, and configuration are often found in patients with polyneuropathies and may be early signs of acute inflammatory demyelinating neuropathy (Guillain-Barré syndrome).

Electrophysiology of radiculopathies

The anatomy, pathophysiology, and clinical evaluation of radiculopathies are discussed. Defining whether root injury is present and which roots are involved can be difficult but critical for patient management. In conjunction with clinical and radiological information, studies that establish physiological abnormalities of roots should be helpful and important. Clinical neurophysiological studies for radiculopathies are performed frequently but have yet to achieve a universally accepted role in the evaluation of these patients. Electrophysiological techniques for the evaluation of radiculopathies are reviewed. Needle electromyography is the best established of these procedures but has the disadvantage of requiring injury to motor fibers of both a certain degree and distribution. Nerve conduction studies may rarely be abnormal in radiculopathies but are needed to be certain other conditions that may produce similar symptoms and signs are not present. H reflexes and F waves probably have roles in the evaluation of radiculopathies but published reports about F waves in radiculopathies have been marred by inadequate methodology. There is evidence based on large series of patients that somatosensory evoked potentials can be helpful for evaluating patients with multilevel injury such as spinal stenosis, patients where electrophysiological studies may have their greatest clinical utility. Further work using either electrical stimulation with needles or magnetic stimulation of roots seems warranted. The demonstration of meaningful electrophysiological changes with activities that reproduce radicular symptoms may be a promising experimental approach. Available information does not necessarily answer critical questions about the role of electrophysiology in patients with radiculopathies. This cannot be done using analyses based on current ideas about evidence based medicine given the absence of a 'gold standard' for defining radiculopathies as well the absence of blinded studies. The available information provides strong arguments for further investigations evaluating different clinical neurophysiological techniques in the same patient, and for evaluating the value of these techniques by concentrating on their clinical import.

Proximal motor conduction evaluated by transcranial magnetic stimulation in acquired inflammatory demyelinating neuropathies

OBJECTIVES

To evaluate conduction abnormalities in the proximal motor nerve in patients with acquired inflammatory demyelinating neuropathies by transcranial magnetic stimulation (TMS).

METHODS

TMS intensity and background voluntary contraction (BVC) to evoke maximal size of motor evoked potential (MEP) in hand muscle were investigated in 24 normal subjects. Effect of experimentally induced conduction block by injecting local anesthetics in the peripheral nerve on MEP size was also studied in two normal subjects. In 22 patients with inflammatory demyelinating neuropathies, maximal MEPs were recorded in the deteriorating and recovery stages of the illness.

RESULTS

In normal subjects, the MEP became maximal with 30-50% of maximal BVC and at more than 80% the maximal stimulator output of the 2.0 T circular coil. The change in MEP size well reflected the degree of conduction block induced by local anesthetics. Findings for patients suggested conduction abnormalities proximal to axilla in 9 patients, and that the abnormal reduction of Erb CMAP was the result of submaximal stimulation, not true conduction block, in 3 patients. The increase in MEP/wrist CMAP ratio was better correlated with improvement in muscle strength than with change in the axilla or Erb CMAP/wrist CMAP ratio.

CONCLUSIONS

Problems such as conduction abnormalities in the motor tract of the central nervous system could not fully be excluded, but we consider that maximal MEP size can be used to predict proximal motor nerve conduction abnormalities.

Aldose reductase inhibition ameliorates pupillary light reflex and F-wave latency in patients with mild diabetic neuropathy

OBJECTIVE

The present study was conducted to investigate the effect of an aldose reductase inhibitor, epalrestat, on autonomic and somatic neuropathy at an early stage in type 2 diabetic patients by assessing the pupillary light reflex and minimum latency of the F-wave.

RESEARCH DESIGN AND METHODS

A total of 30 diabetic patients with subclinical or mild diabetic neuropathy were randomly allocated to a control group (n = 15) and epalrestat (150 mg/day) group (n = 15). After 24 weeks, the pupillary light reflex test, cardiovascular autonomic function tests, and nerve conduction study were performed.

RESULTS

The beneficial effect of epalrestat on the pupillary light reflex was observed in the minimum diameter after light stimuli (P = 0.044), constriction ratio (P = 0.014), and maximum velocity of constriction (P = 0.008). Among cardiovascular autonomic nerve functions, the ratio of the longest expiratory R-R interval to the shortest inspiratory R-R interval during deep breathing was significantly improved by epalrestat (P = 0.037). Minimum latencies of F-wave of median and tibial motor nerves were significantly shortened by epalrestat (P = 0.002 and P = 0.001, respectively); however, no significant effects were observed in motor or sensory nerve conduction velocity.

CONCLUSIONS

These observations suggest that epalrestat may have therapeutic value at the early stage of diabetic neuropathy and that the pupillary light reflex and minimum latency of F-wave may be useful indicators of diabetic neuropathy.

Revisão relacionada a alguns aspectos técnicos e fisiológicos das ondas F e análise dos dados obtidos em um grupo de indivíduos diabéticos

Fazemos uma revisão da literatura e discutimos aspectos fisiológicos relacionados aos tipos de neurônios motores envolvidos na gênese das ondas F. São revistos aspectos técnicos relativos ao número de ondas F a serem colhidas para uma melhor definição dos parâmetros utilizados no estudo destes potenciais. São analisadas as latências, persistência e as velocidades de condução das ondas F registradas nos nervos ulnares em um grupo de indivíduos normais e em um grupo de pacientes diabéticos.

A comparison between different parameters in F-wave studies

Ulnar nerve F-waves were studied in 23 healthy volunteers and 27 diabetic patients. Latencies and chronodispersion were analyzed in each group. In the diabetic group all the parameters were normal in 14 patients (52%) and in 13 (48%) at least one parameter was altered. In these patients the most frequently altered parameter was the maximum latency (92%), followed by mean latency (85%), minimum latency (54%) and chronodispersion (54%). These findings suggest that maximum and mean latencies are better parameters to be analyzed in ulnar F-wave studies than minimum latency.

Remote F-wave changes after local botulinum toxin application

OBJECTIVE

Although the therapeutic effects of botulinum toxin A can be explained by its action at the neuromuscular junction, central or more proximal effects have also been discussed.

METHODS

Eleven patients with torticollis spasmodicus and 3 patients with writer's cramp were studied before and 1 and 5 weeks after the first treatment with botulinum toxin. We measured compound muscle action potentials (CMAPs), motor conduction velocities (MCVs), the shortest (SFL) and the mean F-wave latencies (MFL) and F-wave persistence (30 trials) of untreated muscles for each side (ulnar nerve-abductor digiti minimi muscle, peroneal nerve-tibialis anterior muscle).

RESULTS

CMAPs and MCVs showed no significant changes. For both nerves, however, SFL and MFL were prolonged slightly 1 week after treatment and returned to about baseline after 5 weeks (t test). The F-wave persistence was reduced 1 week after treatment for the right ulnar and both peroneal nerves (t test).

CONCLUSIONS

These results are not likely due to an impairment of neuromuscular transmission. Instead, we propose a decreased excitability of alpha-motoneurons supplying non-treated muscles. A reduction of muscle spindle activity or changes of the recurrent inhibition are discussed as possible causes.

Electrodiagnosis of polyneuropathy

Electrodiagnostic studies comprising electromyography (EMG) and nerve conduction studies (NCS) are well-established objective methods for the diagnosis, quantification and classification of polyneuropathies (PNP). This paper reviews examination techniques, their pathophysiological interpretation, examination strategies and diagnostic criteria for the diagnosis and classification of a PNP. The routine electrodiagnostic evaluation includes sensory NCSs performed with surface or needle electrodes, motor NCSs, F-wave studies and EMG by qualitative or quantitative techniques. Sensory NCSs and F-wave studies have a high sensitivity in PNPs and the different techniques complement each other. The distinction between a PNP with predominantly axonal loss and a PNP with predominantly demyelination is one of the major aims of the electrophysiological examination. There are, however, large variation in suggested criteria for predominantly demyelination. The degree of slowing in conduction taken to indicate demyelination varies between a decrease of 50 to 30% from mean of controls, distal latency prolongation criteria vary from 35% to 70% of mean of controls, F-wave latency prolongation criteria vary from 120% to 150% of upper limit of controls, and criteria for partial motor conduction block vary from 11 to 50% reduction of CMAP amplitude and/or area between proximal and distal stimulation. Needle EMG studies may be valuable in order to detect and quantify denervation activity, to assess chronicity by an evaluation of the extent of reinnervation, and to evaluate the topographical distribution of changes. It is concluded that electrodiagnostic studies are valuable in patients with suspected PNP and the results may have consequences for prognosis and therapy of individual patients. Large variation in examination techniques, strategies, interpretations and diagnostic criteria have been found among electromyographers and it is suggested that the value of electrodiagnostic studies may be further improved by international standardisation.

Nerve conduction studies in amyotrophic lateral sclerosis

We studied 137 ulnar nerves and abductor digiti minimi (ADM) muscles in 70 patients with amyotrophic lateral sclerosis (ALS), and correlated the results with ADM strength graded on the Medical Research Council (MRC) scale, to address the potential value of a standardized neurophysiological assessment of this nerve-muscle system. The ulnar nerves of 35 normal subjects matched for age, gender, and height served as controls. Reduced compound muscle action potential (CMAP) amplitude and area in the ADM muscle recordings correlated strongly with weakness. Distal motor latency, proximal conduction time, and F-wave frequency were abnormal with minimally detectable weakness. In weaker ADM muscles, conduction velocities and F-wave latencies were also abnormal. Conduction block was never observed and sensory potentials were normal. An "ALS neurophysiological index" was derived from these ulnar nerve studies and consisted of the expression: (CMAP amplitude/DML) x F frequency -, where F frequency was expressed as the number of F responses recorded in 20 trials. This index was strongly correlated with ADM weakness (r = 0.74, P < 0.001). Neurophysiological studies restricted to a single nerve-muscle system, the ulnar nerve/ADM, appear potentially useful in objectively assessing change in ALS.

Isolated absence of F waves and proximal axonal dysfunction in Guillain-Barré syndrome with antiganglioside antibodies

OBJECTIVES

To investigate the pathophysiology of selective absence of F waves and its relation with antiganglioside antibodies in Guillain-Barré syndrome (GBS). Some patients with GBS show the absence of F waves as an isolated conduction abnormality, which has been interpreted as demyelination in the proximal nerve segments.

METHODS

In 62 consecutive patients with GBS, sequential nerve conduction and F wave studies were reviewed, and antibodies against ganglioside GM1, GM1b, GD1a, GalNAc-GD1a, GD1b, and GQ1b were measured by an enzyme linked immunosorbent assay.

RESULTS

In the first electrophysiological studies, isolated absence of F waves was found in 12 (19%) patients. Sequential studies in 10 of these patients showed two electrophysiological sequel patterns; rapid restoration of F waves (six patients), and persistent absence of F waves with distal motor nerve degeneration (acute motor axonal neuropathy, four patients). None of the 10 patients showed evidence of demyelination in the proximal, intermediate, or distal nerve segments throughout the course. Of the 62 patients, IgG antibodies against GM1, GM1b, GalNAc-GD1a, or GD1b were significantly associated with the electrodiagnosis of acute motor axonal neuropathy, and patients with these antibodies more often had isolated absence of F waves than patients without them (11 of 36 (31%) v one of 26 (4%); p<0.01). Eleven of the 12 patients with isolated absence of F waves had positive serology for one or more antiganglioside antibodies.

CONCLUSIONS

In GBS with antiganglioside antibodies, isolated absence of F waves is a frequent conduction abnormality especially in the early phase of the disease, and may be caused by axonal dysfunction, such as physiological conduction block or axonal degeneration at the nerve roots.