Multifocal motor neuropathy: electrodiagnostic features

Treatment of multifocal motor neuropathy

OPINION STATEMENT

Multifocal motor neuropathy (MMN) is a treatable immune disorder of the peripheral nerves that is characterized clinically by slowly progressive or stepwise asymmetric distal > proximal, upper > lower limb weakness in multiple motor nerve distributions; electrophysiologically by multifocal motor demyelination, specifically partial motor conduction block; laboratory evidence of high serum anti-GM1 IgM antibodies; and remarkable treatment response to intravenous immunoglobulin (IVIG). IVIG has become the treatment of choice, and the U.S. Food and Drug Administration (FDA) has approved Gammagard Liquid 10 % [immune globulin infusion (human)] as a treatment for multifocal motor neuropathy (MMN). Response to IVIG in MMN is dose- and frequency-dependent, most patients needing high (2 g/kg) and frequent (every 4-8 weeks) doses for several years. Over time, response to IVIG may decrease despite higher and more frequent dosing of IVIG treatment. Subcutaneous immunoglobulin (dose equivalent to IVIG) given in weekly fashion has recently been used with equal efficacy and fewer side effects. There are some case reports and non-randomized trials suggesting variable results from therapeutic or adjunctive use of other immunosuppressive or immunomodulatory agents such as cyclophosphamide, cyclosporine, methotrexate, azathioprine, interferon beta-1a, and rituximab. Of these, cyclophosphamide and rituximab are the only immune treatments that have shown some benefits in case reports. One randomized controlled trial of mycophenolate mofetil used as adjunctive agent did not prove efficacious in altering the disease course. Although MMN, like chronic inflammatory demyelinating polyneuropathy (CIDP), is a chronic immune-mediated demyelinating neuropathy, the use of corticosteroids and plasma exchange - two other therapies used in CIDP - is not beneficial for MMN. Further investigations are warranted to evaluate the immunopathogenesis of MMN and to explore options for dose, frequency, and duration of IVIG treatment as well as the use of alternative immunomodulatory agents either as primary therapeutic or adjunctive agents.

A trial of proficiency of nerve conduction: greater standardization still needed

INTRODUCTION

The aim of this study was to test the proficiency (accuracy among evaluators) of measured attributes of nerve conduction (NC).

METHODS

Expert clinical neurophysiologists, without instruction or consensus development, from 4 different medical centers, independently assessed 8 attributes of NC in 24 patients with diabetes mellitus (DM) on consecutive days.

RESULTS

No significant intraobserver differences between days 1 and 2 were found, but significant interobserver differences were seen. Use of standard reference values did not correct for these observed differences.

CONCLUSIONS

Interobserver variability was attributed to differences in performance of NC. It was of sufficient magnitude that it is of concern for the conduct of therapeutic trials. To deal with interrater variability in therapeutic trials, the same electromyographers should perform all NC assessments of individual patients or, preferably, NC procedures should be more standardized. A further trial is needed to test whether such standardization would eliminate interobserver variability.

Multifocal motor neuropathy, multifocal acquired demyelinating sensory and motor neuropathy, and other chronic acquired demyelinating polyneuropathy variants

Chronic acquired demyelinating neuropathies (CADP) constitute an important group of immune neuromuscular disorders affecting myelin. This article discusses CADP with emphasis on multifocal motor neuropathy, multifocal acquired demyelinating sensory and motor neuropathy, distal acquired demyelinating symmetric neuropathy, and less common variants. Although each of these entities has distinctive laboratory and electrodiagnostic features that aid in their diagnosis, clinical characteristics are of paramount importance in diagnosing specific conditions and determining the most appropriate therapies. Knowledge regarding pathogenesis, diagnosis, and management of these disorders continues to expand, resulting in improved opportunities for identification and treatment.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a rare disorder in which the symptoms are caused by persistent conduction block lesions. The mononeuropathy multiplex progresses over time with increasing axonal loss. The cause of the conduction blocks and axonal loss are not completely understood but immune mechanisms are involved and response to intravenous immunoglobulin has been established. The importance of MMN goes beyond its clinical incidence as the increasing understanding of the pathogenesis of this disorder has implications for other peripheral nerve diseases and for our knowledge of peripheral nerve biology.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) was first described in 1988 as a purely motor neuropathy affecting multiple motor nerves. The diagnosis was based entirely on demonstrating electrophysiological evidence of a conduction block (CB) that selectively affected motor axons, with sparing of sensory axons even through the site of motor CB. Subsequently, a similar disorder was reported but with absence of demonstrable CB on routine nerve conduction studies and there is still some debate as to whether MMN without CB is related to MMN. MMN is thought to be an inflammatory neuropathy related to an immune attack on motor nerves. The conventional hypothesis is that the primary pathology is segmental demyelination, but recent research raises the possibility of a primary axonopathy. Anti-GM1 antibodies can be found in some patients but it is unclear whether these antibodies are pathogenic. Intravenous immunoglobulin is the mainstay of treatment but other immunosuppressive treatments can also be effective.

Concurrence of Multifocal Motor Neuropathy and Hashimoto's Thyroiditis

Background

Multifocal motor neuropathy (MMN) is an immune-mediated disorder that is characterized by slowly progressive and asymmetrical weakness, but its pathophysiological mechanism is uncertain. The hypothesis that MMN is an immunological disease has been supported by the proven therapeutic effects of intravenous immunoglobulin and the detection of antiganglioside antibodies in MMN patients. The coexistence of MMN with other immune diseases has been rarely reported.

Case Report

A 37-year-old woman visited our hospital complaining of weakness in both hands. The clinical manifestations coincided well with MMN: predominantly distal upper-limb weakness, asymmetric involvement, a progressive course, absence of sensory symptoms, absence of pyramidal signs, and sparing of the cranial muscles. The electrophysiological findings also supported a diagnosis of MMN, with motor nerve conduction block in the median, ulnar, and radial nerves, without sensory nerve involvement. The patient was simultaneously diagnosed as having Hashimoto's thyroiditis, which is a well-known immune-mediated disease.

Conclusions

The concurrence of MMN and Hashimoto's thyroiditis in our patient is significant for understanding the immunological characteristics of the two diseases.

Neuropathies associated with conduction block

PURPOSE OF REVIEW

Two disorders, Lewis-Sumner syndrome and multifocal motor neuropathy, are defined by the demonstration of conduction block. These two entities have been intertwined since their description but there are important distinctions between them. It is therefore timely to reconsider these disorders and the physiologic process that defines them.

RECENT FINDINGS

Understanding of the pathophysiology of conduction block has evolved with better understanding of the structure of the node of Ranvier and surrounding apparatus. Axonal excitability studies have begun to give insights into why multifocal motor neuropathy has only motor conduction block. The many published criteria for conduction block vary in sensitivity and specificity and the electromyographer must be aware of the difficulties in determining physiologic block. The distinctions between Lewis-Sumner syndrome and multifocal motor neuropathy have become increasingly clear. Evidence suggests that Lewis-Sumner syndrome is a multifocal variant of chronic inflammatory demyelinating polyneuropathy but that multifocal motor neuropathy is distinct.

SUMMARY

It is important to recognize the distinctions between these disorders, not only because there are important therapeutic issues, but also because a true understanding of the nature of these illnesses will only be accomplished if the overlaps and differences are carefully considered.

Antibody testing in peripheral neuropathies

Many autoantibodies have been described in association with peripheral neuropathy, but the use of antibody testing in clinical practice remains a matter of some debate. Serum autoantibodies to gangliosides or glycoproteins are implicated in a variety of sensory and motor neuropathy syndromes. Paraneoplastic antibodies help identify patients who have a neuropathy related to an underlying malignancy. Detection of an autoantibody in the right clinical setting provides some evidence that the peripheral nerve disturbance is immune mediated and that immunomodulatory therapy may be of benefit.

Multifocal motor neuropathy with conduction block: Distribution of demyelination and axonal degeneration

OBJECTIVE

Multifocal motor neuropathy with conduction block (MMN) is an immune-mediated neuropathy, characterized by progressive muscle weakness. Although demyelination is regarded as the underlying pathophysiologic mechanism of MMN, recently, it was reported that different pathophysiologic mechanisms were responsible for disease in the upper and lower limbs. Specifically, demyelination in the upper limbs and axonal loss in the lower limbs. Consequently, the aim of the present study was to assess, through clinical neurophysiology studies, whether different pathophysiologic mechanisms were occurring in the upper and lower extremities. Furthermore, we wanted to investigate whether the presence of conduction block (CB) correlated with axonal degeneration (AD), and to determine the electrophysiological abnormalities that correlate with muscle weakness.

METHODS

We reviewed medical records of 18 patients with MMN for clinical features (using the Medical Research Council score and Guys Neurology Disability Scale) and neurophysiologic abnormalities (CB, AD prolongation of distal motor and F-wave latencies, and reduction of conduction velocity in the demyelinating range).

RESULTS

Electrophysiological abnormalities deemed specific of demyelination were non-significantly different in the upper and lower extremities. The presence of axonal degeneration correlated significantly with conduction block (odds ratio 10.4, 95% CI 4.2-25.6), and both parameters correlated with muscle weakness (P<0.01).

CONCLUSION

Our study suggests that the same pathophysiologic process occurs in the upper and lower extremity nerves. Moreover, one pathophysiologic process may be responsible for the development of CB and AD, and therefore muscle weakness.

SIGNIFICANCE

The present study has established that both AD and CB occur in MMN, irrespective of extremity, and both correlate with muscle weakness.

Peripheral neuropathy in two patients with rheumatoid arthritis receiving infliximab treatment

Antitumor necrosis alpha agents have been successfully used for the treatment of rheumatoid and seronegative arthritis, Crohn's disease, psoriasis, and severe cases of vasculitis. Several side effects have been observed in patients receiving these agents including hypersensitivity reactions, infections, drug-induced lupus, or demyelinating syndromes. The presence of peripheral neuropathy has been reported only in isolated cases. We describe two cases of peripheral neuropathy which occurred in patients with rheumatoid arthritis receiving infliximab treatment, one with multifocal motor neuropathy with conduction block and another with axonal sensory polyneuropathy, reversed upon discontinuation of infliximab and intravenous gammaglobulin treatment.

Axon loss is an important determinant of weakness in multifocal motor neuropathy

BACKGROUND

Multifocal motor neuropathy (MMN) is characterised by asymmetrical weakness and muscle atrophy, in the arms more than the legs, without sensory loss. Despite a beneficial response to treatment with intravenous immunoglobulins (IVIg), weakness is slowly progressive. Histopathological studies in MMN revealed features of demyelination and axon loss. It is unknown to what extent demyelination and axon loss contribute to weakness. Unlike demyelination, axon loss has not been studied systematically in MMN. Aims/

METHODS

To assess the independent determinants of weakness in MMN, 20 patients with MMN on IVIg treatment were investigated. Using a standardised examination in each patient, muscle strength was determined in 10 muscles. In the innervating nerve of each muscle, axon loss was assessed by concentric needle electromyography, and conduction block or demyelinative slowing by motor nerve conduction studies. Multivariate analysis was used to assess independent determinants of weakness.

RESULTS

Needle electromyography abnormalities compatible with axon loss were found in 61% of all muscles. Axon loss, and not conduction block or demyelinative slowing, was the most significant independent determinant of weakness in corresponding muscles. Furthermore, axon loss and conduction block were independently associated with each other.

CONCLUSION

Axon loss occurs frequently in MMN and pathogenic mechanisms leading to axonal degeneration may play an important role in the outcome of the neurological deficit in patients with MMN. Therapeutic strategies aimed at prevention and reduction of axon loss, such as early initiation of treatment or additional (neuroprotective) agents, should be considered in the treatment of patients with MMN.

Diagnosis and Treatment of Chronic Immune-mediated Neuropathies

The chronic autoimmune neuropathies are a diverse group of disorders, whose diagnosis and classification is based on the clinical presentations and results of ancillary tests. In chronic inflammatory demyelinating polyneuropathy, controlled therapeutic trials demonstrated efficacy for intravenous gamma-globulins, corticosteroids, and plasmaphereis. In multifocal motor neuropathy, intravenous gamma-globulins have been shown to be effective. In the other immune-mediated neuropathies, there are no reported controlled therapeutic trials, but efficacy has been reported for some treatments in non-controlled trials on case studies. Choice of therapy in individual cases is based on reported efficacy, as well as severity, progression, coexisting illness, predisposition to developing complications, and potential drug interactions.

A practical definition of conduction block in IvIg responsive multifocal motor neuropathy

BACKGROUND

Multifocal motor neuropathy with conduction block (MMN) can be mistaken for motor neurone disease or other lower motor neurone syndromes, but is treatable with intravenous immunoglobulin (IvIg). Formal electrophysiological criteria for conduction block (CB) are so stringent that substantial numbers of patients may miss out on appropriate treatment.

METHODS

Electrophysiological data were collected from 10 healthy volunteers and compared to data from 10 patients who satisfied the clinical criteria for MMN and who responded to IvIg. This produced a definition of CB in MMN patients which was compared with existing definitions to assess "miss rates".

RESULTS

Mean values for compound muscle action potential area, amplitude, and duration were calculated in normal subjects. Results beyond 3 SD of their respective means were considered abnormal. Using these criteria, CB in the context of MMN was defined as a reduction in negative peak area >23% along a distal nerve segment or >29% across a proximal segment; or a reduction in amplitude >32% across a distal segment or >33% across a proximal segment. All IvIg responsive patients had at least one nerve segment showing such CB. Employing some criteria from the literature would have denied treatment to over 30% of responsive patients.

CONCLUSION

In the clinical setting of suspected MMN, less stringent criteria for CB can improve the diagnosis of this treatable disorder. Exclusions on grounds of temporal dispersion may be over-restrictive. A little over one third of CBs occur proximally.

The effect of treatment upon temporal dispersion in IvIg responsive multifocal motor neuropathy

BACKGROUND

Multifocal motor neuropathy with conduction block (MMN) is a treatable disorder that can be mistaken for other lower motor neurone syndromes. Existing electrophysiological diagnostic criteria for MMN are restrictive. In particular, many are cautious about diagnosing conduction block (CB) in the presence of abnormal temporal dispersion (TD).

OBJECTIVE

To study the significance of TD in MMN, its relationship to CB in intravenous immunoglobulin (IvIg) responsive patients, and its utility in detecting a treatment response.

METHODS

We compared pre- and post-treatment changes in CB and TD in nine patients who satisfied clinical and electrophysiological criteria for MMN and responded to IvIg.

RESULTS

TD improved in one or more nerve segments in eight of nine patients tested. There was marked improvement in 65% of all nerve segments, and 60% of those segments with CB. By comparison, significant improvement in CB occurred in only 33% of segments. Of segments with significantly better CB after treatment, all but one showed similar improvements in TD. Such changes were not related to the degree of TD before treatment, being seen in segments with abnormal as well as normal TD. There was no correlation between improvements seen in TD and CB.

CONCLUSION

We believe that TD should be considered an inherent feature of MMN. Improvement in TD is an independent marker of electrophysiological improvement in this disorder and is likely to be more useful than CB. When MMN is clinically suspected, the use of stringent criteria for CB in the presence of TD should be avoided.

Multifocal motor neuropathy: current concepts and controversies

Multifocal motor neuropathy (MMN) is now a well-defined purely motor multineuropathy characterized by the presence of multifocal partial motor conduction blocks (CB), frequent association with anti-GM1 IgM antibodies, and usually a good response to high-dose intravenous immunoglobulin (IVIg) therapy. However, several issues remain to be clarified in the diagnosis, pathogenesis, and therapy of this condition including its nosological position and its relation to other chronic dysimmune neuropathies; the degree of CB necessary for the diagnosis of MMN; the existence of an axonal form of MMN; the pathophysiological basis of CB; the pathogenetic role of antiganglioside antibodies; the mechanism of action of IVIg treatments in MMN and the most effective regimen; and the treatment to be used in unresponsive patients. These issues are addressed in this review of the main clinical, electrophysiological, immunological, and therapeutic features of this neuropathy.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is an immune-mediated disorder characterised by slowly progressive, asymmetrical weakness of limbs without sensory loss. The clinical presentation of MMN mimics that of lower-motor-neuron disease, but in nerve-conduction studies of patients with MMN motor-conduction block has been found. By contrast with chronic inflammatory demyelinating polyneuropathy, treatment with prednisolone and plasma exchange is generally ineffective in MMN and even associated with clinical worsening in some patients. Of the immunosuppressants, cyclophosphamide has been reported as effective but only anecdotally. Various open trials and four placebo-controlled trials have shown that treatment with high-dose intravenous immunoglobulin leads to improvement of muscle strength in patients with MMN. Although clinical, pathological, imaging, immunological, and electrophysiological studies have improved our understanding of MMN over the past 15 years, further research is needed to elucidate pathogenetic disease mechanisms in the disorder.

Intravenous immunoglobulin for multifocal motor neuropathy

BACKGROUND

Multifocal motor neuropathy is a rare, probably immune mediated disorder characterised by slowly progressive, asymmetric, distal weakness of one or more limbs with no objective loss of sensation. It may cause prolonged periods of disability. The treatment options for multifocal motor neuropathy are sparse. Patients with multifocal motor neuropathy do not usually respond to steroids or plasma exchange, and may even worsen with these treatments. Many uncontrolled studies have suggested a beneficial effect of intravenous immunoglobulin.

OBJECTIVES

To review systematically the evidence from randomised controlled trials concerning the efficacy and safety of intravenous immunoglobulin in multifocal motor neuropathy.

SEARCH STRATEGY

We used the search strategy of the Cochrane Neuromuscular Disease Review Group to search the Disease Group register (searched September 2003), MEDLINE (January 1990 to September 2003), EMBASE (January 1990 to September 2003) and ISI (January 1990 to September 2003) databases for randomised controlled trials.

SELECTION CRITERIA

Randomised controlled studies examining the effects of any dose of intravenous immunoglobulin versus placebo in patients with definite or probable multifocal motor neuropathy. Outcome measures had to include one of the following: disability, strength, or conduction block. Studies which reported the frequency of adverse effects were used to assess safety.

DATA COLLECTION AND ANALYSIS

Two authors reviewed literature searches to identify potentially relevant trials, scored their quality and extracted data independently. For dichotomous data, we calculated relative risks, and for continuous data, effect sizes and weighted pooled effect sizes. Statistical uncertainty was expressed with 95% confidence intervals.

MAIN RESULTS

Four randomised controlled trials including a total of 34 patients were suitable for this systematic review. Strength improved in 78% of patients treated with intravenous immunoglobulin and only 4% of placebo-treated patients. Disability improved in 39% of patients after intravenous immunoglobulin treatment and in 11% after placebo (statistically not significantly different). Mild, transient side effects were reported in 71% of intravenous immunoglobulin treated patients. Serious side effects were not encountered.

AUTHORS' CONCLUSIONS

Limited evidence from randomised controlled trials shows that intravenous immunoglobulin has a beneficial effect on strength. There was a non-significant trend towards improvement in disability. More research is needed to discover whether intravenous immunoglobulin improves disability and is cost-effective.

Magnetic stimulation using a triple-stimulation technique in patients with multifocal neuropathy without conduction block

It has been suggested previously that multifocal motor neuropathy (MMN) without conduction block (CB) or other features of demyelination is axonal in nature. Conventional transcranial magnetic stimulation (TMS) and the triple-stimulation technique (TST) performed on 10 MMN patients without CB revealed a proximal focal CB in 4 patients. In 3 other patients, the amplitude ratio obtained in response to conventional TMS was abnormally low, but the area ratio was normal. The TST amplitude ratio and area ratio were normal in these 3 patients. This pattern suggested the occurrence of temporal dispersion without CB. The occurrence of temporal dispersion or CB was associated with a relatively satisfactory response to intravenous immunoglobulins. These findings suggest that some forms of MMN previously thought to be axonal are in fact proximal variants of MMN with CB.

Neuropathies motrices multifocales avec blocs de conduction persistants : 18 ans après

Multifocal motor neuropathy with persistent conduction blocks was firstly reported in 1986 and outlined from the group of purely motor diseases of the peripheral nervous system. The main criterion is the presence of conduction blocks located only on the motor nerves; additionally 30 percent of patients have IgM subclass serum antibodies directed against GM1 ganglioside. The clinical picture is a multifocal, asymmetrical, neuropathy, starting and predominant in the upper limbs, occurring in males aged 50 years and more, and having a progressive course. There is no biological sign besides elevated anti-GM1 antibodies. CSF analysis discloses mild increased protein count. The course is unpredictable, the neuropathy may be strictly limited to one or two motor nerves, or spread to other motor nerves in the four limbs. There is no involvement of the sensory and the cranial nerves, no involvement of the autonomic and the central nervous system. The pathophysiology is unknown, animal models do not allow to confirm the role of humoral immunity, and the role of anti-GM1 antibodies is controversial. Randomized controlled trials have assessed the efficacy of intravenous immunoglobulins which dramatically improve strength in 70-80 percent of patients in the short term, but remain unable to prevent motor deterioration in most patients, together with the occurrence of new conduction blocks. Corticosteroids and plasma exchanges do not improve the patients and may be followed by transient worsening. Long-term efficacy of immunosuppressive agents is not known.

On the early diagnosis of IVIg-responsive chronic multifocal acquired motor axonopathy

Multifocal acquired motor axonopathy (MAMA) is a treatable, immune mediated motor neuropathy with purely axonal electrophysiological features. Distinction from degenerative neuronopathies such as progressive muscular atrophy (PMA) or early motor neuron disease (MND) can be difficult because of the similar clinical and electrophysiological findings. Here, we report the clinical, electrophysiological and laboratory findings in 6 patients with MAMA. Electrophysiological testing showed purely axonal findings with evidence of pathological spontaneous activity and chronic neurogenic changes. Of particular note, pathological spontaneous activity in paraspinal myotoms was not detectable in any of the patients even though it had been documented in peripheral muscles of the corresponding myotome(s). Elevated serum ganglioside antibody levels,most frequently anti-GD1a antibodies, were present in all 6 patients. IV Ig treatment led to clinical improvement in all but one patient, who showed an allergic response when exposed to IVIg. Our findings indicate that paraspinal EMG and anti-GD1a antibodies can facilitate the early identification of treatable, IVIg responsive, patients with MAMA.

Autoimmune neuropathies

Autoimmune neuropathies are common and treatable disorders of the peripheral nerves, which should be properly recognized. This article discusses their diagnosis, differential diagnosis and proper treatment.

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.

Demyelinating focal motor neuropathy of the ulnar nerve masquerading as compression in Guyon's canal: a case report

Ulnar nerve-innervated intrinsic muscle weakness, in the absence of sensory complaints or deficits, usually is the result of compression at the ulnar nerve in zone II of Guyon's canal. In rare instances the problem is not caused by a compressive neuropathy but by a demyelinating focal motor neuropathy. Demyelinating neuropathies have been well documented in the neurologic literature but they have received little attention in the hand surgery literature. We report on one such case and the importance of differentiating the 2 neuropathies. Although surgery often is necessary for a compressive neuropathy it is contraindicated for a demyelinating neuropathy.

Anterior interosseous nerve and multifocal motor neuropathy

We report the case of a 47-year-old woman with a left anterior interosseous nerve palsy. Surgical release of the anterior interosseous nerve was initially proposed, but electrodiagnostic evaluation demonstrated that the neuropathy was due not to compression or to neuralgic amyotrophy but to a proximal conduction block. At that time, the conduction block could be defined only by indirect electrodiagnostic criteria. A multifocal motor neuropathy with persistent conduction block was subsequently diagnosed, and the patient was treated with intravenous immunoglobulins. The efficacy of this treatment and the subsequent disclosure of conduction block in the right posterior interosseous and peroneal nerves definitively confirmed the multifocal motor neuropathy.

Nerve conduction studies in selected peripheral nerve disorders

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Electrodiagnostic approach to the patient with suspected motor neuron disease

The diagnosis of amyotrophic lateral sclerosis (ALS) per se may be challenging since there is no single diagnostic test for ALS (with the exception of finding a mutation in the SOD1 gene). Additionally, the disease may begin focally and resemble a variety of other neurologic disorders that share clinical features with ALS. This latter point emphasizes an important imperative for the clinician--the need to consider a broad range of peripheral and central nervous system disorders in the process of differential diagnosis of ALS, especially when the disease is in its early stages. The authors review the diagnostic criteria for ALS and discuss which features to consider in determining the degree of certainty or level of confidence in the diagnosis. The authors then enumerate the important differential diagnostic possibilities that emerge from a careful consideration of the clinical features and comment on neuroimaging studies and laboratory tests employed in the diagnostic process. Next, the authors turn their attention to the important role played by electrophysiologic studies in the diagnostic evaluation of the patient with suspected ALS. The authors then return to a focused consideration of selected disorders in the differential diagnosis of ALS and conclude with a summary of their diagnostic approach for this disease.

Secondary amyloidosis as a life-ending event in multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a disorder of peripheral nerve often associated with a high monosialoganglioside (GM1) antibody and multifocal conduction block. It has a chronic, indolent course with involvement of predominantly peripheral motor nerves, usually in an asymmetric fashion. There have been few reported cases of progression to frank quadriplegia. Secondary amyloidosis refers to the deposition of amyloid in various tissues due to an underlying chronic inflammatory state. We report the first case, to our knowledge, of a patient with MMN associated with high titer of GM1 antibody who developed acute paraplegia with both cranial nerve and worsening sensory involvement associated with multiorgan compromise due to a secondary amyloidosis involving the myocardium.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) is a recently identified peripheral nerve disorder characterized by progressive, predominantly distal, asymmetric limb weakness mostly affecting upper limbs, minimal or no sensory impairment, and by the presence on nerve conduction studies of multifocal persistent partial conduction blocks on motor but not sensory nerves. The etiopathogenesis of MMN is not known, but there is some evidence, based mostly on the clinical improvement after immunological therapies, that the disease has an immunological basis. Antibodies, mostly IgM, to the gangliosides GM1, and though less frequently, GM2 and GD1a, are frequently detected in patients' sera, helping in the diagnosis of this disease. Even if there is some experimental evidence that these antibodies may be pathogenic in vitro, their role in the neuropathy remains to be established. Patients with MMN do not usually respond to steroids or plasma exchange, which may occasionally worsen the symptoms, while the efficacy of cyclophosphamide is limited by its relevant side effects. More than 80% of MMN patients rapidly improve with high dose intravenous immunoglobulin therapy (IVIg). The effect of this therapy is, however, transient and improvement has to be maintained with periodic infusions. A positive response to interferon-beta has been recently reported in a minority of patients, some of whom were resistant to IVIg. Even if many progresses have been made on the diagnosis and therapy of MMN, there are still several issues on the nosological position, etiopathogenesis and long-term treatment of this neuropathy that need to be clarified.

Asymmetric Acquired Demyelinating Polyneuropathies: MMN and MADSAM

More than a half a century after Austin's initial description of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), the clinical spectrum of chronic acquired demyelinating polyneuropathies has expanded. Currently there are a number of entities that can be put under the heading of chronic acquired demyelinating neuropathy (CADP) based on differing clinical presentations. In this scheme, CIDP is used only to refer to patients with demyelinating neuropathies and generalized symmetric weakness. In contrast, multifocal motor neuropathy (MMN) and multifocal acquired demyelinating sensory and motor neuropathy (MADSAM) fall into the category of asymmetrical, multifocal forms of CADP. These are distinguished from each other only by the presence of sensory involvement. In our opinion, there are pragmatic reasons for splitting these clinical presentations into distinct entities. Although each of these clinical subtypes shares some basic similarities, there are important differences. MMN is usually considered resistant to corticosteroid therapy and the first line agent in this disorder is intravenous immunoglobulin (IVIg). MADSAM neuropathy can be responsive to prednisone or IVIg, and has a profile more analogous to classic CIDP with regards to its laboratory features and treatment response.

Clinical spectrum of chronic acquired demyelinating polyneuropathies

A number of presentations of chronic demyelinating polyneuropathy have been identified, each distinguished by its phenotypic pattern. In addition to classic chronic inflammatory demyelinating polyneuropathy (CIDP), which is characterized clinically by symmetric proximal and distal weakness and sensory loss, several regional variants can be recognized: multifocal motor neuropathy (MMN: asymmetric and pure motor), multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy (asymmetric, sensory, and motor), and distal acquired demyelinating symmetric (DADS) neuropathy (symmetric, distal, sensory, and motor). There are also temporal, pathological, and disease-associated variants. This review describes a clinical scheme for approaching the chronic acquired demyelinating polyneuropathies that leads to a rational use of supportive laboratory studies and treatment options. In addition, we propose new diagnostic criteria for CIDP that more accurately reflect current clinical practice.

Electrodiagnostic studies in amyotrophic lateral sclerosis and other motor neuron disorders

The clinical electrodiagnostic medicine (EDX) consultant asked to assess patients with suspected amyotrophic lateral sclerosis (ALS) has a number of responsibilities. Among the most important is to provide a clinical assessment in conjunction with the EDX study. The seriousness of the diagnoses and their enormous personal and economic impact require a high-quality EDX study based on a thorough knowledge of and experience with motor neuron diseases (MNDs) and related disorders. Clinical evaluation will help determine which of the EDX tools available to the EDX consultant should be applied in individual patients. Although electromyography (EMG) and nerve conduction study are the most valuable, each of the following may be helpful in the assessment of selected patients based on their clinical findings: repetitive nerve stimulation, motor unit number estimate, single-fiber EMG, somatosensory evoked potential, autonomic function test, and polysomnography. The pertinent literature on these is reviewed in this monograph. The selection and application of these EDX tools depend on a thorough knowledge of the MNDs and related disorders.

Natural history of 46 patients with multifocal motor neuropathy with conduction block

We studied 46 consecutive patients with multifocal motor neuropathy with conduction block (MMN-CB). Typically, asymmetric weakness and atrophy of the hands or arms developed insidiously, but spontaneous improvement (without treatment) or death from this disease did not occur and 94% remained employed. For 18 patients examined on multiple occasions using the weakness subscore of the neuropathy impairment score [NIS(W)] for a median time of 2.3 years, worsening of 1.3 points per year was observed; many patients, however, had received intensive immunomodulating therapy. Median worsening to our first evaluation (generally without treatment) was estimated at 4.2 points per year, perhaps suggesting that treatment had influenced course. Three criteria for conduction block (CB) were compared, but the least stringent was sensitive for the diagnosis. Conduction block accompanied by weakness and atrophy typically affected only motor fibers, especially of midforearm nerves, and these sites of dysfunction persisted for months or years. Neurological signs and electrodiagnostic features were consistent with CB, axonal degeneration, a variable degree of reinnervation, and segmental demyelination. Although this study did not focus on therapy, intravenous gammaglobulin and cyclophosphamide appeared to be associated with neurological improvement, which was seldom complete or sustained. Axonal degeneration and faulty regeneration may in part explain this muted response. Possibly, treatment must be earlier, more intense, or different.

Chronic demyelinating hypertrophic brachial plexus neuropathy

A patient with unilateral, painless, chronic progressive upper limb sensorimotor deficit showed electrophysiological evidence of a focal demyelinating neuropathy with almost complete conduction block across the brachial plexus. Magnetic resonance imaging disclosed marked brachial plexus hypertrophy. Intravenous immunoglobulin led to fast and complete recovery, maintained by intermittent perfusions. Hypertrophic brachial plexus neuropathy can be a presentation of focal chronic inflammatory demyelinating polyradiculoneuropathy. Objective and quantitative assessment of hand function is useful to evaluate treatment results and to optimize treatment regimens.

Multifocal acquired demyelinating sensory and motor neuropathy: the Lewis-Sumner syndrome

We report 11 patients with multifocal acquired demyelinating sensory and motor (MADSAM) neuropathy, defined clinically by a multifocal pattern of motor and sensory loss, with nerve conduction studies showing conduction block and other features of demyelination. The clinical, laboratory, and histological features of these patients were contrasted with those of 16 patients with multifocal motor neuropathy (MMN). Eighty-two percent of MADSAM neuropathy patients had elevated protein concentrations in the cerebrospinal fluid, compared with 9% of the MMN patients (P < 0.001). No MADSAM neuropathy patient had elevated anti-GM1 antibody titers, compared with 56% of MMN patients (P < 0.01). In contrast to the subtle abnormalities described for MMN, MADSAM neuropathy patients had prominent demyelination on sensory nerve biopsies. Response to intravenous immunoglobulin treatment was similar in both groups (P = 1.0). Multifocal motor neuropathy patients typically do not respond to prednisone, but 3 of 6 MADSAM neuropathy patients improved with prednisone. MADSAM neuropathy more closely resembles chronic inflammatory demyelinating polyneuropathy and probably represents an asymmetrical variant. Given their different clinical patterns and responses to treatment, it is important to distinguish between MADSAM neuropathy and MMN.