Sensitivity and specificity of diagnostic criteria for conduction block in chronic inflammatory demyelinating polyneuropathy

Conduction slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies: Electrophysiology meets pathology

Nerve conduction studies are usually the first diagnostic step in peripheral nerve disorders and their results are the basis for planning further investigations. However, there are some commonplaces in the interpretation of electrodiagnostic findings in peripheral neuropathies that, although useful in the everyday practice, may be misleading: (1) conduction block and abnormal temporal dispersion are distinctive features of acquired demyelinating disorders; (2) hereditary neuropathies are characterized by uniform slowing of conduction velocity; (3) axonal neuropathies are simply diagnosed by reduced amplitude of motor and sensory nerve action potentials with normal or slightly slow conduction velocity. In this review, we reappraise the occurrence of uniform and non-uniform conduction velocity slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies attempting, with a translational approach, a correlation between electrophysiological and pathological features as derived from sensory nerve biopsy in patients and animal models. Additionally, we provide some hints to navigate in this complex field.

Compound muscle action potential duration ratio for differentiation between Charcot-Marie-Tooth disease and CIDP

OBJECTIVE

To elucidate the utility of the proximal to distal compound muscle action potential (CMAP) duration ratio to distinguish between demyelinating Charcot-Marie-Tooth disease (CMT) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) compared with nerve ultrasound.

METHODS

Thirty-nine demyelinating CMT patients and 19 CIDP patients underwent nerve conduction studies (NCS) and nerve ultrasound. NCS parameters including CMAP duration ratio calculated by dividing the value at the proximal site by that at the distal site and nerve cross-sectional area (CSA) measured by ultrasound were compared between the two groups. The diagnostic sensitivity and specificity of each parameter were analysed.

RESULTS

CMT patients showed a significantly lower CMAP duration ratio than CIDP patients (p < 0.05). The area under the curve (AUC) value of the CMAP duration ratio exceeded 0.95 when CMT was considered "positive", and a cut-off value of 1.13 resulted in high diagnostic sensitivity and specificity (84.6 and 100 % for median nerve, 97.4 and 85.7 % for ulnar nerve, respectively), whereas the AUC value of nerve CSA ranged from 0.70 to 0.81.

CONCLUSIONS

The CMAP duration ratio could effectively distinguish between demyelinating CMT and CIDP.

SIGNIFICANCE

Adding the CMAP duration ratio to a routine NCS may improve the accuracy of the diagnosis of demyelinating CMT.

A novel locus for a hereditary recurrent neuropathy on chromosome 21q21

Hereditary recurrent neuropathies are uncommon. Disorders with a known molecular basis falling within this group include hereditary neuropathy with liability to pressure palsies (HNPP) due to the deletion of the PMP22 gene or to mutations in this same gene, and hereditary neuralgic amyotrophy (HNA) caused by mutations in the SEPT9 gene. We report a three-generation family presenting a hereditary recurrent neuropathy without pathological changes in either PMP22 or SEPT9 genes. We performed a genome-wide mapping, which yielded a locus of 12.4 Mb on chromosome 21q21. The constructed haplotype fully segregated with the disease and we found significant evidence of linkage. After mutational screening of genes located within this locus, encoding for proteins and microRNAs, as well as analysis of large deletions/insertions, we identified 71 benign polymorphisms. Our findings suggest a novel genetic locus for a recurrent hereditary neuropathy of which the molecular defect remains elusive. Our results further underscore the clinical and genetic heterogeneity of this group of neuropathies.

[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.

Pathophysiology inferred from electrodiagnostic nerve tests and classification of polyneuropathies. Suggested guidelines

OBJECTIVE

To present criteria for pathophysiological interpretation of motor and sensory nerve conduction studies and for pathophysiological classification of polyneuropathies suggested by a group of European neurophysiologists.

METHODS

Since 1992 seven neurophysiologists from six European countries have collected random samples of their electrodiagnostic examinations for peer review medical audit in the ESTEEM (European Standardized Telematic tool to Evaluate Electrodiagnostic Methods) project. Based on existing criteria in the literature, the experience with a patient material of 572 peer reviewed electrodiagnostic examinations, and productive discussions between the physicians at workshops, the collaboration has produced a set of criteria now routinely used at the centres involved in the project.

RESULTS

The first part of the paper considers pathophysiology of individual nerve segments. For interpretation of motor and sensory nerve conduction studies, figures showing change in amplitude versus change in conduction velocity/distal latency and change in F-wave frequency versus change in F-wave latency are presented. The suggested boundaries delimit areas corresponding to normal, axonal, demyelinated, or neuropathic nerve segments. Criteria for motor conduction block in upper and lower extremities are schematically depicted using the parameters CMAP amplitude and CMAP duration. The second part of the paper suggests criteria for classification of polyneuropathies into axonal, demyelinating, or mixed using the above-mentioned criteria.

CONCLUSIONS

The suggested criteria are developed during many years of collaboration of different centres and may be useful for standardization in clinical neurophysiology.

SIGNIFICANCE

Consistent interpretation of nerve conduction studies is an important step in optimising diagnosis and treatment of nerve disorders.

A case of severe congenital chronic inflammatory demyelinating polyneuropathy with complete spontaneous remission

Chronic inflammatory demyelinating polyneuropathy (CIPD) is characterised by progressive weakness, hyporeflexia and electrophysiological evidence of demyelination with maximal neurological deficit reached after at least 8 weeks progression. CIPD rarely affects children. We present a neonate with clinical features compatible with congenital CIPD. A term male infant of non-consanguineous parents was referred to us at birth with weakness and contractures affecting his legs, suggesting a prenatal onset of immobility. He also had evidence of bulbar dysfunction with poor suck, recurrent aspiration and requiring nasogastric feeding. He had no antigravity movements in the legs, bilateral wrist drop, distal joint contractures and absent deep tendon reflexes. Electromyography showed neurogenic changes, with nerve conduction velocities markedly reduced, increased distal motor latency and dispersed compound muscle action potentials. Cerebrospinal fluid protein was raised. Sural nerve biopsy demonstrated decreased numbers of myelinated fibres and inflammatory cell infiltrates. Muscle biopsy showed denervation. He only received supportive treatment and by 6 months he had fully recovered, and all electrophysiological parameters had normalised.

Neurophysiologic findings in early acute inflammatory demyelinating polyradiculoneuropathy

BACKGROUND

Patients with early acute inflammatory demyelinating polyradiculoneuropathy (AIDP) may not meet the current neurophysiologic criteria.

OBJECTIVE

To document neurophysiologic findings in early AIDP.

METHODS

Clinical and neurophysiologic data from 38 AIDP patients, assessed within 10 days of symptom onset were reviewed.

RESULTS

In addition to absent H reflexes and abnormal F-wave responses in the acute stage of AIDP, abnormalities of blink reflexes, upper limb sensory responses abnormalities with spared sural responses, presence of distal CMAP dispersion, and A-waves were frequently observed. Established demyelinating neurophysiologic parameters were infrequently seen.

CONCLUSIONS

Abnormalities of H reflexes and F responses were most frequently noted in early AIDP. Additionally, distal temporal dispersion, prolonged or absent blink reflexes, and A-waves were often present in the acute stage of AIDP when classic diagnostic criteria of AIDP were not satisfied.

SIGNIFICANCE

Neurophysiologic studies in early AIDP frequently reveal abnormalities that are not specific of primary demyelinating neuropathy.

A novel stop codon mutation in the PMP22 gene associated with a variable phenotype

The most frequent inherited peripheral neuropathy is the peripheral myelin protein 22 (PMP22) gene related disease. Duplication, deletion, and point mutations in that gene are associated with phenotypic variability. Here we report a family carrying a novel mutation in the PMP22 gene (c. 327C>A), which results in a premature stop codon (Cys109stop). The family members who carry this mutation have a Charcot-Marie-Tooth type 1 variable phenotype, ranging from asymptomatic to severely affected. These findings suggest that the fourth transmembrane domain of the PMP22 gene may play an important role, although the intrafamilial clinical variability reinforces the observation that pathogenic mutations are not always phenotype determinant and that other factors (genetic or epigenetic) modulate the severity of the clinical course.

Marinacci communication: an electrophysiological study

OBJECTIVE

Prevalence of Martin-Gruber anastomosis, an anomalous median-to-ulnar forearm communication, is well reported in literature while Marinacci communication, the reverse of Martin-Gruber with a forearm ulnar-to-median communication is under-recognized. We systematically evaluated the presence of Marinacci communication in a series of patients referred for electrophysiological studies.

METHODS

One hundred consecutive patients referred to the electrophysiological laboratory for various diagnoses were studied using standard techniques for motor, sensory and f wave studies.

RESULTS

Of the 100 patients (200 arms) studied, electrophysiological features of Marinacci communication were observed in 4 patients (7 arms). Median stimulation with recording over abductor pollicis brevis (APB) revealed a pseudo-conduction block over the forearm segment while on ulnar stimulation and recording over abductor digiti minimi (ADM), the amplitude of the compound muscle action potential (CMAP) obtained on proximal stimulation was higher than that obtained on distal stimulation. Ulnar stimulation at the elbow but not at the wrist revealed CMAP from APB without initial positivity. Its amplitude was 50% of the amplitude obtained on median stimulation at the wrist.

CONCLUSIONS

Marinacci communication is not uncommon in the general population. A pseudo-conduction block on median stimulation and higher CMAP amplitude on proximal than distal stimulation provide valuable clues to its recognition.

Inter-nerves and intra-nerve conduction heterogeneity in CMTX with Arg(15)Gln mutation

OBJECTIVE

In X-linked Charcot-Marie-Tooth disease (CMTX), electrophysiological and histopathological studies have suggested either a demyelinating or an axonal polyneuropathy. We report a CMTX family with a striking heterogeneity of nerve conductions between and within nerves.

METHODS

Two men and one woman have been studied by conduction velocities, sural nerve biopsy with morphometry (one man) and DNA analysis.

RESULTS

In both men motor conduction velocities were slowed in the demyelinating range, conduction velocity differences among nerves in the same subject varied from 13 to 24 m/s, and distal median compound muscle action potential (CMAP) amplitudes were 3-5 times reduced compared to ulnar CMAPs. Abnormal area reduction or excessive temporal dispersion of proximal CMAP was present in at least two nerves in all patients. Sural nerve biopsy showed reduction of large myelinated fibres, cluster formations, occasional onion bulbs. Teased fibres study revealed short internodes for fibre diameter, enlarged Ranvier nodes but no evidence of segmental demyelination and remyelination. DNA analysis showed an Arg(15)Gln mutation in connexin32 gene in all patients.

CONCLUSIONS

In this family conduction slowing and segmental conduction abnormalities, in absence of morphological evidence of de-remyelination, may be related to short internodes, widened Ranvier nodes and the specific effect of the mutation. The occurrence in some CMTX patients of a non uniform involvement between and within nerves, as in acquired demyelinating neuropathies, should be kept in mind to avoid misdiagnoses.

Variation in the classification of polyneuropathies among European physicians

OBJECTIVE

Considerable debate still exists regarding the classification of polyneuropathies (PNPs) into predominantly demyelinating, predominantly axonal loss, mixed or unclassified. This study was designed to determine the variation among physicians in the classification of PNPs by using the European Standardized Telematic tool to Evaluate Electromyography knowledge-based systems and Methods (ESTEEM) multicenter database.

METHODS

Seven physicians from 6 laboratories in Europe sent a total of 156 prospectively collected cases of PNP with electromyography (EMG) data including diagnosis (examination diagnosis) to the database. Each physician interpreted the electrophysiological data from all cases (interpretation diagnosis) and a final diagnosis was given at the consensus meetings of the group (consensus diagnosis).

RESULTS

Comparison of each physician's examination diagnosis with his/her interpretation diagnosis, i.e. intra-physician variation, showed a change towards less classified PNPs (P < 0.05). Interpretation diagnoses showed large inter-physician variation in the classification of PNPs. The consensus group was more cautious than individual physicians in classifying PNPs as mixed and axonal. The probability of the consensus diagnosis increased with increasing number of abnormal motor and sensory segments tested.

CONCLUSIONS

Recognition of variation in classification of PNP as shown in this study and suggesting standards of good clinical practice developed by a consensus group may increase the quality of EMG practice.

Can electrophysiology differentiate polyneuropathy with anti-MAG/SGPG antibodies from chronic inflammatory demyelinating polyneuropathy?

OBJECTIVES

Patients with polyneuropathy and antibodies to myelin-associated glycoprotein (MAG) and sulphated glucuronyl paragloboside (SGPG) differ from chronic inflammatory demyelinating polyneuropathy (CIDP) because of a slower, progressive course, symmetrical and predominantly sensory involvement of legs, predominantly distal slowing of motor conductions, and poorer response to therapy. We studied whether a wide set of electrophysiologic parameters may differentiate these two neuropathies.

METHODS

We reviewed the electrophysiological studies of 10 patients with anti-MAG/SGPG antibodies and 22 with CIDP examining: (1) motor conduction velocity and distal compound muscle action potential amplitude; (2) conduction block (CB) and temporal dispersion; (3) distal motor latency and terminal latency index (TLI); (4) F wave and proximal conduction time; and (5) sensory conduction and occurrence of abnormal median with normal sural sensory potential.

RESULTS

Anti-MAG/SGPG neuropathies showed: (1) more severe involvement of peroneal nerves; (2) more frequent disproportionate distal slowing of motor conductions (TLI< or =0.25) and absent sural potential, and (3) no CB. However 3/22 CIDP patients also had at least two nerves with TLI< or =0.25 and no CB.

CONCLUSIONS

Electrophysiologic findings suggest in anti-MAG/SGPG neuropathy a length-dependent process with a likely centripetal evolution. A disproportionate slowing of conduction in distal segments of motor nerves suggests the diagnosis of anti-MAG/SGPG neuropathy, although it is not pathognomonic.

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.

Sensitivity and specificity of different conduction block criteria

OBJECTIVES

To resolve the discrepancy between conduction block criteria derived from healthy controls and stricter criteria suggested by computer simulation of interphase cancellation through altered motor units.

METHODS

An EMG database provided control nerves from patients with amyotrophic lateral sclerosis (ALS) or neural muscular atrophy (CMT1) (disease controls) and from subjects without neuromuscular diseases (healthy controls). We estimated normal limits from the healthy controls (criterion A) and from the pooled sample of healthy and disease controls (criterion B). We compared their sensitivity with that of an arbitrary limit of 0.5 (criterion C) in acute (AIDP) and chronic inflammatory demyelinating neuropathy (CIDP) and in multifocal motor neuropathy (MMNP). Specificity was assessed in ALS and CMT1.

RESULTS

Limits estimated from healthy controls (criterion A: amplitude ratio of <0.7 in median and peroneal nerves and <0.8 in the ulnar nerve) gave false positive results in 17.3% of the ALS nerves. High scatter of the amplitude ratio of the nerves with distal response amplitudes below 1 mV required amplitude-dependent limits (0.36 for distal responses below 1 mV, 0.56 between 1 and 2 mV, and between 0.67 and 0.73 for higher response amplitudes) for criterion B. It was false positive in 4.3% of the ALS nerves and in 28.3% of the CMT1 nerves. A limit of 0.5 for nerves with distal responses above 1 mV and a limit of 0.36 for smaller responses (criterion D) avoided false positive results in ALS without further impairing sensitivity per patient in MMNP. Sensitivity in AIDP was 34.9% for criterion A, 19.5% for criterion B, and 10.2% for criterion D. Amplitude ratios were more sensitive than area ratios in CIDP and MMNP, but less specific in CMT1.

CONCLUSIONS

Limits derived from healthy controls are unspecific in chronic neuromuscular diseases and in nerves with low response amplitudes. Criterion D should be used if motor unit restructuring or conduction delays have to be taken into account. Criterion A may be applicable in early AIDP if the distal response amplitude is above 1 mV.

Peroneal neuropathy after weight loss

The objectives of this study were to evaluate the clinical and electrophysiological findings in peroneal mononeuropathies following a weight-reduction diet. Thirty patients with acute peroneal palsy and weight loss were studied. Complete nerve conduction studies (NCS) were performed in upper and lower limbs. NCS showed conduction block (CB) of the peroneal nerve at the fibular head that recovered in 29 patients within 3 weeks to 3 months. Severity of CB was correlated with clinical weakness. Three patients had abnormalities consistent with polyneuropathy (PNP). NCS in asymptomatic relatives confirmed familial neuropathy. Nerve biopsy and molecular study were consistent with hereditary neuropathy with liability to pressure palsies (HNPP). One of these peroneal palsies (6 months) recovered after neurolysis. Weight loss might be a risk factor in peroneal mononeuropathies. NCS is a tool in the diagnosis of the site and severity of the nerve injury. Testing should be considered for relatives of patients with PNP because peroneal mononeuropathies may be the first expression of HNPP.

Minimal and asymptomatic chronic inflammatory demyelinating polyneuropathy

OBJECTIVES

Show the chronic inflammatory demyelinating polyneuropathy (CIDP) is not only clinically heterogeneous but extremely variable in severity.

METHODS

Three patients were referred for mild distal paresthesiae lasting more than 6 months and one for inguinal and thigh pain later ascribed to coxarthrosis. Strength was normal in all patients and tactile sensation reduced distally only in one. Tendon jerks were absent, except the knee jerks in one patient, reduced in lower limbs in two and normal in one.

RESULTS

Electrophysiology showed a demyelinating neuropathy without motor conduction block. CSF protein content was increased in all patients. Nerve biopsies showed de-remyelination with varying degrees of axonal loss. Genetic studies excluded a demyelinating neuropathy associated with duplication or deletion of the 17p.11.2 segment.

CONCLUSIONS

CIDP patients with pure sensory clinical presentation have been described but are generally more severely impaired. However, because of the mildness of symptoms and the unequivocal electrophysiological involvement of motor fibers, we think that in these cases the term minimal CIDP is more appropriate than sensory CIDP. These cases represent the most benign end of the CIDP spectrum. In our series minimal or even asymptomatic CIDP encompasses 8% of cases.

Chronic inflammatory demyelinating polyneuropathy in diabetics: motor conductions are important in the differential diagnosis with diabetic polyneuropathy

OBJECTIVE

It is important to recognize CIDP occurring in diabetics because, unlike diabetic polyneuropathy, it is treatable. The aim of this study was to find out whether there are clues which help to differentiate CIDP in diabetics from diabetic polyneuropathy.

METHODS

We compared the electrophysiological and pathological findings of 7 diabetics, who developed a predominantly motor polyneuropathy with the features of CIDP, with a group of diabetics referred for symptomatic polyneuropathy.

RESULTS

Of the 7 diabetics we believe developed CIDP, 6 met at least 3 and one patient two of the 4 electrophysiological criteria of demyelination. Of the 100 patients referred for diabetic polyneuropathy, only 4 fulfilled two criteria and none 3. Nerve biopsy findings were not helpful in differential diagnosis, as segmental demyelination and remyelination, onion bulbs and inflammatory infiltrates, which are the histologic features of CIDP, were also present in diabetic polyneuropathy.

CONCLUSIONS

CIDP can be diagnosed in a diabetic patient when motor symptoms are predominant, are more severe than expected in diabetic polyneuropathy and 3 of the 4 electrophysiological criteria for demyelination are fulfilled. When only two criteria are met, we believe that a trial with one of the established treatments for CIDP may be helpful in confirming the diagnosis.

Kugelberg lecture: principles and pitfalls of nerve conduction studies

Optimal application of the nerve conduction study depends on an understanding of the principles and a recognition of the pitfalls of the technique. The conventional methods deal primarily with distal nerve segments in an extremity. Other techniques allow one to assess nerve segments in less accessible anatomical regions, to improve the accuracy in precisely localizing a focal lesion, and to increase the sensitivity in detecting subclinical abnormalities. Despite certain limitations, nerve conduction studies can provide diagnostically pertinent information if they are used judiciously in the appropriate clinical contexts.

Decrease in nerve temperature: a model for increased temporal dispersion

A decrease in nerve temperature causes a proportional decrease in conduction velocity which, in percentage terms, is equal for all nerve fibers. The absolute decrease in conduction velocity is larger for faster conducting nerve fibers. This results in a compression and a shift to lower values of the conduction velocity distribution and an increase in temporal dispersion. The purpose of this study was to determine if these effects could be detected by a combination of two collision techniques designed to obtain the motor conduction velocity distribution and refractory period distribution. In 12 healthy volunteers we measured the conduction velocity distribution in the median nerve at nerve temperatures of 25 and 40 degrees C. The results showed that our method could detect the predicted changes in conduction velocity distribution and temporal dispersion. We conclude that temperature change is a model that can be used to study temporal dispersion. This may be a first step towards distinguishing between the effects of conduction block and (abnormal) temporal dispersion in demyelinated nerve fibers.

Childhood chronic inflammatory demyelinating polyneuropathy

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a chronic disorder of the peripheral nervous system with sensory and motor involvement, and insidious onset over a period of months. In children and adults, both proximal and distal muscles are affected. Muscle stretch reflexes are absent or depressed. Laboratory findings include elevated cerebrospinal fluid protein with no increase of mononuclear cells. Electrophysiological and pathological studies show evidence of demyelination. No control studies of the efficacy of immunomodulating therapy in childhood CIDP are available. However, several studies have indicated clinical improvement after treatment with prednisolone, plasmapheresis and intravenous immunoglobulin, but disappointing results with other immunosuppressive agents. While some children have a monophasic course, with complete recovery, others have a protracted course, with either a slowly progressive or a relapsing-remitting course, resulting in prolonged morbidity and disability.

Chronic dysimmune demyelinating polyneuropathy: a clinical and electrophysiological study of 93 patients

OBJECTIVES

To identify clinical, electrophysiological, and immunological characteristics of chronic immune demyelinating polyneuropathy to define for each group the appropriate therapeutic strategies.

METHODS

The clinical and electrophysiological data and the response to treatment of 93 patients with an acquired chronic dysimmune demyelinating polyneuropathy (CDDP) studied over a period of 10 years were reviewed. Two groups were identified: group 1, comprising 64 patients with an idiopathic CDDP, of whom 13 had serum monoclonal or polyclonal gammopathy without detectable antibodies directed against the "myelin associated glycoprotein" (MAG), and group 2, comprising 29 patients with an IgM monoclonal gammopathy of undetermined significance (MGUS) with antibodies binding to the MAG.

RESULTS

Group 1 patients had either a progressive or relapsing course. The relapsing course had more pronounced distal slowing of motor conduction velocity. In group 1, there were no significant clinical or electrophysiological differences between patients with or without gammopathy. Patients with anti-MAG antibody (group 2) differed significantly from group 1 patients, especially on the basis of electrophysiological results. They had a more pronounced slowing of peroneal motor nerve conduction velocity, a lower frequency of conduction block, and a distal accentuation of conduction slowing, distinguishing them from those with idiopathic CDDP, Charcot-Marie-Tooth polyneuropathy type 1A, and control subjects.

CONCLUSION

The idiopathic CDDP group is heterogeneous with probably different subgroups. Patients with IgM MGUS polyneuropathy and anti-MAG antibodies have characteristics which distinguish them significantly from other CDDP and suggest different immune mechanisms and responses to treatment.

The F wave disappears due to impaired excitability of motor neurons or proximal axons in inflammatory demyelinating neuropathies

OBJECTIVES

Investigation of pathophysiology of F wave disappearance in demyelinating neuropathies.

METHODS

The peripheral motor nerve conduction was studied by motor evoked potential (MEP) on transcranial magnetic stimulation as well as conventional nerve conduction studies before and after the treatment in 26 patients with inflammatory demyelinating neuropathies. In addition, serum antiganglioside antibodies in the acute or active stage were examined.

RESULTS

The F wave was abolished in 10 patients. Seven of the 10 patients showed motor evoked potentials (MEPs) on transcranial magnetic stimulation that ranged from 1-4 mV. In six of them the F wave reappeared in the recovery stage, but the MEP size did not change. This may be caused by humoral factors, because the F wave reappeared immediately after plasma exchange or intravenous immunoglobulin treatment. A correlation of F wave disappearance with the presence of serum antiganglioside antibodies was found.

CONCLUSIONS

The major pathophysiology of F wave disappearance in demyelinating neuropathies is impairment of motor neuron excitability or prolonged refractoriness of the most proximal axon for backfiring. The conventional interpretation that absent F waves suggest a conduction block at the proximal site is often inadequate.

Proximal and segmental motor nerve conduction in the sciatic nerve produced by percutaneous high voltage electrical stimulation

Percutaneous high voltage electrical stimulation was applied to the proximal sciatic nerve at the hip in 18 normal subjects to evaluate motor conduction in the proximal sciatic nerve, and short-segment stimulation of the sciatic and posterior tibial nerves was given in 6 normal subjects. Compound muscle action potentials (CMAPs) were recorded from the abductor hallucis (AH) and extensor digitorum brevis (EDB) muscles. Supramaximal stimulation was easily obtained at the proximal sciatic nerve and all the sites in the short-segment stimulation. The motor nerve conduction velocity of the sciatic nerve between the hip and the popliteal fossa was 49.2 +/- 4.24 m/sec in the tibial division and 54.1 +/- 6.48 m/sec in the peroneal division. The respective peak-to-peak amplitude and negative-peak areas of the CMAPs at the hip were reduced to 86.8 +/- 5.65% and 97.3 +/- 5.36% for the tibial division, and 93.4 +/- 7.06% and 96.8 +/- 5.09% for the peroneal division as compared to the values for the popliteal fossa. The negative-peak duration of the CMAPs at the hip point were increased to 109.2 +/- 7.2% for the tibial nerve and 107.1 +/- 5.68% for the peroneal nerve as compared with the duration at the popliteal fossa. This method is non-invasive and useful for evaluating motor nerve conduction in the lower limb.

Chronic progressive steroid responsive axonal polyneuropathy: a CIDP vaariant or a primary axonal disorder?

Five patients presented with chronic,, progressive, predominantly motor polyneuropathy. CSF protein content was increased in 4 patients. Motor conduction velocities and EMG were consistent with axonal involvement. Sural nerve conductions were normal in all cases and sural nerve biopsy performed in 1 patient was normal. Serum antibodies to GM1, GD1a, GD1b, and GM2 were negative. All patients improved after steroid treatment and 3 completely recovered. Because of therapeutic implications it is important to differentiate these patients from those with chronic idiopathic axonal neuropathies. It is unclear whether this is a primary axonal, probably immune-mediated, polyneuropathy, or whether it represents one extreme of the chronic inflammatory demyelinating polyradiculoneuropathy spectrum characterized by severe axonal loss. We suggest that the term "chronic inflammatory polyneuropathy," encompassing cases from pure demyelinating to pure axonal neuropathies responsive to steroids, should be reinstated and that, like in Guillain-Barré syndrome, different subtypes should be individuated.

Differential electrophysiological features of neuropathies associated with 17p11.2 deletion and duplication

Hereditary neuropathy with liability to pressure palsies (HNPP) and hereditary motor-sensory neuropathy type IA (HMSN IA) are quite distinct clinical entities recently associated to deletion and duplication, respectively, of the 17p11.2 segment including the gene for peripheral myelin protein 22 (PMP-22). We studied the electrophysiological features of 48 HNPP and 62 HMSN IA motor nerves. Conduction velocities (CV) and compound muscle action potential amplitudes were significantly reduced and distal latencies prolonged in HMSN IA compared to HNPP. CV was uniformly slowed in HMSN IA nerves whereas in HNPP it was focally slowed in 80% of ulnar and 12% of peroneal nerves at usual compression sites. Conduction block was present in 6% of HNPP nerves but in none of HMSN IA.

IN CONCLUSION

(1) HMSN IA with 17p11.2 duplication presents marked, diffuse, and uniform slowing; (2) HNPP with 17p11.2 deletion presents focal electrophysiological abnormalities possibly correlated with the presence of tomaculae; and (3) under- and overexpression of PMP-22 in concurrence with environmental factors might be responsible for the distinctive features of HNPP and HMSN IA.

Quantitative analysis of the compound muscle action potential in early acute inflammatory demyelinating polyneuropathy

We quantitated the size and configuration of compound muscle action potentials (CMAPs) in 266 nerves (66 median, 67 ulnar, 71 tibial and 62 peroneal) of 72 patients with acute inflammatory demyelinating polyneuropathy (AIDP) initially studied within 19 days of symptom onset. Results were compared with criteria for CMAP abnormalities, including criteria for abnormal negative peak duration and desynchronisation, derived from a control population of 50 median, ulnar, tibial and peroneal nerves. Other motor conduction abnormalities including minimal F response latency were also examined. We also analysed patterns of CMAP abnormality, peak disability and outcome for AIDP patients who had at least 3 motor nerves evaluated at first electrophysiologic study. Amongst AIDP nerves, low amplitude of the distal CMAP, usually with prolonged distal latency, was much more common than an abnormal fall in CMAP amplitude between stimulus sites. Using our CMAP criteria more than half of these low amplitude distal responses showed prolonged negative peak duration of desynchronisation or both, consistent with demyelination. Of the 47 AIDP patients who had 3 or more nerves initially studied, 37 (78.7%) had at least 1 motor nerve with a distal CMAP showing evidence of temporal dispersion. In addition, those with at least 75% of motor nerves showing a pattern of low amplitude of the distal CMAP without a further significant fall in amplitude between stimulus sites had greater peak disability and a poorer outcome. Assessment of temporal dispersion of the distal CMAP should be included in electrophysiologic criteria for acute demyelination. In addition, for some patients with AIDP patterns of CMAP amplitude abnormality amongst motor nerves are present early in the illness and may provide prognostic information.