Multifocal acquired demyelinating neuropathy masquerading as motor neuron disease

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.

Results of testing for anti-GM1 antibodies

We used an ELISA technique to measure IgG and IgM antibodies to the ganglioside GM1, with the results expressed in arbitrary units. We tested 1007 sera from patients with peripheral neuropathy or muscle weakness. For IgG and IgM antibodies, the distribution of results differed significantly from a normal distribution. In the patient group, 81 of 1007 sera had elevated levels of IgG antibodies (> 10 units). Of these, 11 patients had very high levels (> 50 units). These 11 patients had diagnoses of GBS (4), motor neurone disease (3) or non-specific idiopathic neuropathy (4). For IgM antibodies, 115 of 1007 sera were positive (> 20 units). Of these, 18 patients had very high levels (> 50 units). These 18 patients had diagnoses of Guillain-Barré syndrome or Miller Fisher syndrome (4), multifocal motor neuropathy (4), motor neurone disease (2), non-specific neuropathy (2). We conclude that anti-GM1 antibodies in high titre are uncommon. Patients with multifocal motor neuropathy have high levels of antibody. However, patients with other disorders may also have high levels, so that anti-GM1 antibody levels alone are not a specific test for multifocal motor neuropathy. We found that antibodies to GM1 were present in the sera of patients with chronic idiopathic neuropathy, leading us to suggest that these antibodies may sometimes arise as a secondary response to disease.

Chronic motor axonal neuropathy associated with antibodies monospecific for N-acetylgalactosaminyl GD1a

We report on three patients with chronic motor neuropathy who had elevated titers of immunoglobulin (Ig)G antibodies against N-acetylgalactosaminyl GD1a (GalNAc-GD1a) and normal titers of antibodies against other gangliosides. Presenting with progressive muscular atrophy, fasciculations, and no sensory deficits, the patients had been diagnosed to have motor neuron disease. Electrodiagnostic features were predominantly axonal. Two patients clinically improved after intravenous Ig infusion and cyclophosphamide therapy. Increased titers of IgM antibodies to GalNAc-GD1a were also found in two of 15 patients with multifocal motor neuropathy with conduction block but were associated with concomitant rise of anti-GM1 antibodies. These three cases represent a chronic motor axonal neuropathy in which antibody testing for a minor ganglioside was helpful for instituting therapy.

Multifocal motor neuropathy mimicking motor neuron disease: nine cases

Multifocal motor neuropathy with persistent conduction block (MMN) is a rare clinical entity, mimicking motor neuron disease (MND). In order to research which are the most frequent nerves and segments where conduction block (CB) can be identified, we reviewed the clinical and neurophysiological data of nine patients with MMN who were studied and followed by the authors. Weakness and muscle atrophy of the dominant hand was the most frequent presentation. Lower limbs were involved later in the disease evolution. The ulnar and median nerves were the most affected nerves. They had conduction blocks mostly at the forearm and at Erb's point-elbow (or above elbow) segments. Both common peroneal and tibial nerves were frequently affected at their distal segments, but proximal segments were also probably involved. The presence of anti-GM1 antibodies was variable, and their determination was not essential for the diagnosis of MMN. Eight patients given IV immunoglobulin therapy had no disease progression. One patient was responsive to corticosteroids. The CB identification in our patients allowed us to clearly distinguish MMN from MND. The good prognosis and need for management with IV immunoglobulin, support the crucial role of a careful neurophysiological study to diagnose this clinical entity.

Entrapment neuropathies

Entrapment neuropathies occur when nerves are chronically compressed or mechanically injured at specific locations. Some of these focal neuropathies such as carpal tunnel syndrome are common, and others such as neurogenic thoracic outlet syndrome are rare. This article highlights recent advances and interesting observations that cover a wide spectrum of such focal neuropathies. Selected disorders that can affect individual peripheral nerves and masquerade as 'entrapment neuropathies' are also emphasized.

Evaluation and rehabilitation of patients with adult motor neuron disease

Adult motor neuron disease (amyotrophic lateral sclerosis [ALS]) is a neurodegenerative disorder characterized by loss of motor neurons in the cortex, brain stem, and spinal cord, manifested by upper and lower motor neuron signs and symptoms affecting bulbar, limb, and respiratory musculature. Clinically, the disease course is characterized by progressive weakness, atrophy, spasticity, dysarthria, dysphagia, and respiratory compromise, ultimately resulting in death or mechanical ventilation in the vast majority of patients. Patterns of presentation and pathological features of the disease, along with clinical and electrophysiologic criteria for diagnosis, are discussed in this review. Since 8% to 22% of patients survive more than 10 years without ventilator use, meticulous medical and rehabilitation management is extremely important to ensure optimal health and quality of life in these patients. Major issues in the care of individuals with ALS include weakness and spasticity, impairments in activities of daily living and mobility, communication deficits and dysphagia in those with bulbar involvement, respiratory compromise, fatigue and sleep disorders, pain, and psychosocial distress. Research in ALS changes rapidly, but is currently focused on potential etiologic factors such as glutamate excitotoxicity, role of oxidative stress, autoimmunity to calcium channels, and cytoskeletal abnormalities, as well as related treatment initiatives including glutamate modulators, neurotrophic factors, antioxidants, antiapoptotic factors, and gene therapy. Recently, mutations in the gene encoding Cu/Zn superoxide dismutase were identified in a subset of familial ALS patients. Riluzole, a glutamate antagonist and Na-channel blocker, became the only drug currently approved for treatment of ALS after studies showed a small positive effect on survival. Until a definitive treatment or cure for ALS is found, the multifaceted rehabilitation team approach remains the best hope for improving health and survival in this devastating illness.

Central motor conduction time in patients with multifocal motor conduction block

The finding of conduction block (CB) within short consecutive segments along a motor nerve is a key feature of multifocal motor neuropathy (MMN). Despite their different pathogenesis, this may be the only clinical difference between some cases of MMN and the pure spinal muscular atrophy form of motor neuron disease (MND). In 12 patients with distal atrophy and fasciculations and electrophysiological evidence of CBs in the upper limbs, we measured the peripheral and central motor conduction times (PMCT and CMCT) to hand muscles. We reasoned that patients with MMN should show an abnormally prolonged PMCT with normal CMCT, whereas an increased CMCT would suggest MND. All patients had delayed F-wave latency and increased PMCT. Three patients had increased CMCT. Follow-up showed little clinical and electrophysiological change in 7 of the 9 patients with normal CMCT, and a progressive motor deficit leading ultimately to death in 1 of the 3 patients with increased CMCT. This patient's electrophysiological follow-up showed a significant decrement of the compound motor action potential to both proximal and distal stimulation points, with disappearance of earlier CBs. Autopsy revealed loss of anterior horn cells and axons of the ventral root, and degeneration of large myelinated fibers. We conclude that determining the CMCT may help in differentiating MND from MMN. Persistence of a stable clinical picture over a span of at least 1 year and lack of electrophysiological signs of involvement of upper motor neurons should both be required before establishing the diagnosis of MMN even with electrophysiological evidence of CB.

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.

Assessment of temporal dispersion in motor nerves with normal conduction velocity

Demyelinated nerves attenuate high-frequency components of propagating action potentials. In order to study if there is diagnostic use of this in motor nerves, the spectral energy above 49 Hz, amplitude, area, and duration of the compound muscle action potentials were measured; values after distal and proximal stimulation of posterior tibial nerves were compared. Normative data were collected in 48 control subjects. The same measurements were made in 20 patients with polyneuropathy and reduced motor nerve conduction velocity, in 21 patients with mild polyneuropathy but normal motor nerve conduction velocity, and in 8 patients with myasthenia gravis. Overall, high-frequency attenuation was closely correlated with amplitude decay (r = 0.63, P<10(-19)) and with increase of action potential duration (r = 0.34, P = 10(-5)). In the group of patients with normal NCV, high-frequency attenuation was abnormal in 9 (43%), amplitude decay was abnormal in two (10%), and area decay was abnormal in one (5%) patient. The action potential duration was normal in all of these patients. High-frequency attenuation was not influenced by stimulus intensity, thus it is not changed by conduction block, and it was not influenced by impaired neuromuscular transmission. Hence, high-frequency attenuation, both sensitively and specifically does indicate abnormal temporal dispersion. In conclusion, the simple measurement of high-frequency attenuation markedly improves detection and characterization of demyelination of human motor fibers.

Response to therapy in demyelinating motor neuropathy

We reviewed results of immunotherapy in patients with demyelinating motor neuropathy (DMN), and found that patients over 50 years of age at onset responded poorly, and younger patients responded variably to intervention. We suggest that patients with DMN be given a guarded prognosis, particularly if >50 years of age at onset.

Treatment of chronic inflammatory demyelinating polyneuropathy

The management of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is the main topic of this review. A few comments will also be made about treatment of the demyelinating form of paraproteinaemic demyelinating polyneuropathy (PDN) and of multifocal motor neuropathy (MMN). The review briefly describes the main characteristics of these neuropathies, and examines case series and trials which evaluated the principal therapeutic strategies for CIDP, PDN and MMN, such as intravenous immunoglobulin (IVIg) therapy, steroid treatment, plasma exchange and immunosuppressor administration. Controlled trials demonstrated that IVIg, steroid treatment and plasma exchange are effective in CIDP. For PDN the therapeutic strategies are the same as for idiopathic CIDP, but usually the clinical response is poorer. For MMN, IVIg therapy is definitely the first choice treatment.

Diagnosis of amyotrophic lateral sclerosis

This review of the differential diagnosis of amyotrophic lateral sclerosis focuses on two themes. The first is practical, how to establish the diagnosis based primarily on clinical findings buttressed by electrodiagnosis. The main considerations are multifocal motor neuropathy and cervical spondylotic myelopathy. The second theme is the relationship of motor neuron disease to other conditions, including benign fasciculation (Denny-Brown, Foley syndrome), paraneoplastic syndromes, lymphoproliferative disease, radiation damage, monomelic amyotrophy (Hirayama syndrome), as well as an association with parkinsonism, dementia and multisystem disorders of the central nervous system.

Multifocal motor neuropathy with conduction block misdiagnosed as multiple entrapment neuropathies

We describe a 58-year-old male with a few years history of multifocal weakness in the upper limbs with minimal to absent sensory complaints. He was diagnosed as having multiple compressive neuropathies, which required repeated decompressive surgeries. Electrodiagnostic studies prior to diagnosis were limited to a few nerves, evaluating only distal segments. Because of delay in making the diagnosis, his condition progressed, and possibly because of the unnecessary surgeries, he developed atrophy in some muscles, which resulted in significant motor disability. He was later diagnosed as having multifocal motor neuropathy with conduction block and has partially responded to intravenous immunoglobulin therapy.

Human autoimmune neuropathies

Peripheral nerve diseases are among the most prevalent disorders of the nervous system. Because of the accessibility of the peripheral nervous system (PNS) to direct physiological and pathological study, neuropathies have traditionally played a unique role in developing our understanding of basic mechanism of nervous system injury and repair. At present they are providing new insight into the mechanisms of immune injury to the nervous system. A rapidly growing catalogue of PNS disorders are now suspected to be immune-mediated, and in the best understood of these disorders, the molecular and cellular targets of immune attack are known, and the pathophysiology follows directly from the specific immune injury. This review summarizes the immunologically relevant features of the PNS, then considers selected immune-mediated neuropathies, focusing on pathogenetic mechanisms. Finally, the PNS is providing a testing ground for new immunotherapies and approaches to protection and regeneration, including the use of trophic factors. The current status of treatment and implications for future approaches is reviewed.

Demyelinating polyneuropathy with preferentially-proximal involvement

A 47-year-old man showed progressive, symmetrical weakness in the limbs for 6 months. There was muscle atrophy, fasciculations, and acute denervation without motor conduction abnormalities below the elbows or knees, and motor neuron disease had once been suspected. However, compound muscle action potentials (CMAPs) after proximal stimulation showed an amplitude reduction between axilla and Erb's point for the median and ulnar nerves on both sides. His weakness as well as the amplitude reduction improved after administration of prednisolone. Demyelinative conduction abnormalities can be limited to the proximal segments for at least several months in a conduction equivalent to chronic inflammatory demyelinating polyneuropathy (CIDP).

Multifocal motor neuropathy without overt conduction block

One of the defining electrophysiological characteristics of multifocal motor neuropathy (MMN) is focal motor nerve conduction block. We have noted occasional patients with typical clinical features of MMN in whom there is no demonstrable conduction block. Upon review of 5 such cases, we conclude that otherwise typical MMN may present without overt conduction block. This subset of patients does not otherwise differ from patients with MMN in whom this hallmark electrodiagnostic feature is present.

Intravenous immunoglobulin treatment of neurological autoimmune diseases

Intravenous immunoglobulin (IVIg) has been widely used in neurological diseases during the last decade. The current indications of IVIg in neurological diseases are reviewed and discussed on the basis of the available experimental data and clinical trials. Compared to other immunomodulating treatments used in neurological diseases, IVIg has only few side effects with a small risk of transmission of infectious agents. Good clinical evidence for the effectiveness is available for Guillain-Barré-Syndrome, chronic inflammatory demyelinating polyneuropathy and multifocal motor neuropathy. In conditions like myasthenia gravis and myositis favourable effects of IVIg were reported, but future studies have to be awaited. For all other neurological conditions where IVIg has been administered, there is currently no support for the use of IVIg other than in controlled trials. In conclusion, IVIg is a promising immunomodulary therapy that has been shown to be effective in some neurological autoimmune diseases. Routine use in neurological practice should be restricted to diseases for which a positive effect has been proven in controlled trials. For all other conditions no definite recommendations can presently be made.

Long term effect of intravenous immunoglobulins and oral cyclophosphamide in multifocal motor neuropathy

OBJECTIVES

To report the long term effect of the combined treatment with high dose intravenous immunoglobulins (i.v.Ig) and oral cyclophosphamide (CTX) in patients with multifocal motor neuropathy, and to determine whether the association of oral CTX in these patients may help to delay and, possibly, suspend i.v.Ig infusions.

METHODS

Six patients with multifocal motor neuropathy responding to an initial course of i.v.Ig (0.4 g/kg/day for five consecutive days) were followed up for 37 to 61 (mean 47) months. All patients were subsequently treated with periodic i.v.Ig infusions (0.4 g/kg/day for two days at clinical worsening) and oral CTX (1-3 mg/kg/day). Improvement was assessed using the Rankin disability scale, a functional impairment scale for upper and lower limbs, and the MRC rating scale on the 20 most affected muscles. Electrophysiological and antiglycolipid antibody studies were performed before treatment, then yearly during follow up.

RESULTS

All patients improved during treatment and, by the end of follow up or before worsening after therapy suspension, the median Rankin (P=0.0335) and upper (P=0.0015) and lower limb (P=0.0301) impairment scores and the mean MRC (P=0.0561) score were improved. By that time the number of nerves with partial motor conduction block was reduced (P=0.0197) and antiglycolipid antibody titres had decreased in all but one patient. All patients required periodic i.v.Ig infusions to maintain improvement but, after three to seven months of oral CTX, the interval between i.v.Ig infusions could be progressively prolonged until, in three patients, both treatments could be stopped for up to two years before clinical worsening. The main complications, both related to oral CTX, were haemorrhagic cystitis in two patients and persistent amenorrhea in one patient.

CONCLUSIONS

I.v.Ig can induce and maintain improvement in multifocal motor neuropathy but does not eradicate the disease. Oral CTX may help to induce a sustained remission but it is not devoid of side effects and might therefore be reserved for patients with multifocal motor neuropathy who require frequent i.v.Ig infusions to maintain improvement.

[Multifocal motor neuropathy: an individualized disease of the peripheral nervous system]

Multifocal motor neuropathy is a peripheral nervous system disease described among chronic inflammatory demyelinating polyneuropathies. It is characterized according to both clinical criteria, including chronic asymmetric and multifocal deficit which starts and remains prominent in the upper limbs, and electrophysiological criteria, including persistent multifocal motor conduction blocks in motor nerves. High titers of serum antiganglioside GM1 antibodies are discovered in nearly 40% of cases. Steroids and plasma exchange are not efficient. High doses of intravenous immunoglobulins (i.v.Ig) improved symptoms in the majority of open and controlled published studies. The quality of the response to i.v.Ig may worsen in some patients after a variable number of infusions, leading to immunosuppressive treatments mainly with oral or intravenous cyclophosphamide. Its etiology is unknown but the frequent presence of anti-GM1 antibody high serum titers, the pathological findings in some rare morphological studies, and the response to i.v.Ig favor the hypothesis of an autoimmune disorder.

Long term follow up of multifocal motor neuropathy with conduction block under treatment

Eighteen patients (15 men, three women; age range 30 to 71 years, mean 45.8 years) with multifocal motor neuropathy treated with high dose intravenous immunoglobulin (IVIg) were evaluated for nine to 48 months (mean follow up 25.3 months). The median time between onset of multifocal motor neuropathy and treatment was 5.8 years. The dose of IVIg was 0.4 g/day for three to five days. The interval between each treatment was determined for each patient by the evaluation of the effect of the first course. Muscle strength was evaluated by a computerised analyser. Clinical improvement was seen in 12 patients treated with IVIg (67%). Isometric strength increased from 32% to 97% (mean 54.5%) of the initial value. Functional scales corroborated these findings. No clear predictive factors of response to IVIg was found except the presence of high titres of IgM anti-GM1 antibodies. Often, patients needed repeated courses of IVIg to maintain the improvement. In two patients, IVIg infusions were stopped without signs of relapse after one year. Four patients were initially treated with prednisone (1 mg/kg/day), without any clear improvement. Five patients with no response to IVIg or who were IVIg dependent were treated with cyclophosphamide, but only one showed improvement. These results show the long term benefits and safety of IVIg in multifocal motor neuropathy but also the transient effect of this expensive treatment in most patients.

Intravenous immunoglobulin treatment in multifocal motor neuropathy and other chronic immune-mediated neuropathies

This review deals with the use of intravenous IVIg immunoglobulins in the treatment of chronic immune-mediated neuropathies: multifocal motor neuropathy, chronic inflammatory demyelinating polyneuropathy, neuropathies associated with monoclonal gammopathies. A particular attention is given to case series and trials which compare IVIg to other therapies, such as steroid treatment immunosuppressors and plasma exchange. At present clinical and instrumental data seem to indicate the short term efficacy of IVIg in multifocal motor neuropathies, especially as early treatment; further studies are need in order to prove its long term efficacy in this disease. Concerning chronic inflammatory demyelinating polyneuropathies, short term IVIg efficacy is comparable to that of plasma exchange and in the long term most patients need repeated treatments. Most patients respond to the initial therapy and the initial nonresponders usually improve with a second treatment modality.

Motor nerve biopsy studies in motor neuropathy and motor neuron disease

The clinical presentation of motor neuropathy often resembles that of motor neuron disease, sometimes leading to an erroneous diagnosis. Moreover, the underlying pathological process in motor neuropathy has been rarely investigated and there are no systematic studies of the affected motor nerves. We describe a new motor nerve biopsy procedure, performed in 15 patients: 6 with motor neuropathy and 9 with motor neuron disease. The motor branch from the anterior division of the obturator nerve to the gracilis muscle in the thigh was biopsied. In both groups of patients the motor nerves exhibited depletion of myelinated nerve fibers. In motor neuropathy there was a significantly higher density of regenerative clusters of small myelinated fibers in comparison to motor nerves from patients with motor neuron disease. In addition, in 3 patients with motor neuropathy there was evidence for demyelination with thinly myelinated axons and small onion bulb formations. These pathological studies of motor nerve biopsies can help to differentiate motor neuropathy from motor neuron disease.

Pitcher's arm: an electrodiagnostic enigma

Every major league baseball pitcher, most minor league pitchers, but only few amateur pitchers that we have studied have had reduced sensory nerve action potentials in the throwing arm. We present 6 clinical cases which demonstrate the spectrum of "pitcher's arm." These cases suggest that the phenomenon is a pathologic process, probably an example of a repetitive use syndrome affecting the brachial plexus. Although it does not appear to impact performance, it has clear implications for the interpretation of electrodiagnostic studies in symptomatic pitchers.

Motor neuropathies mimicking amyotrophic lateral sclerosis/motor neuron disease

We report three patients in whom the initial diagnosis was of possible A myotrophic lateral sclerosis (ALS/MND) according to the 'El Escorial Criteria'. All of them presented with monomelic paresis, atrophy of the paretic muscles and generalised brisk reflexes. The initial electromyograms showed a neurogenic pattern in the limbs with normal sensory and motor conduction velocities. Laboratory evaluation and imagiological investigations were normal in all of them. The previous diagnosis was changed in to demyelinating motor neuropathy with conduction block in 2 patients and tomaculous neuropathy in one after clinical and electromyographic follow-up and nerve biopsy. Patients 1 and 2 were given intravenous immunoglobulin treatment and showed moderate improvement.

Chronic immune-related demyelinating neuropathies

In recent years many important advances have been made in the knowledge of the mechanisms that may produce peripheral nerve damage. Data in the literature indicate that in some chronic demyelinating neuropathy autoantibodies against myelin antigens may play a pathogenic role. The pathogenic role of T cells, cytokines, complement, and class II molecules has also been studied. Identification of specific immune-related demyelinating polyneuropathies provides clues to future therapeutic approaches. This paper focuses on the chronic inflammatory demyelinating polyneuropathy, chronic demyelinating neuropathies associated with monoclonal gammapathies of undetermined significance, and multifocal motor neuropathy, and reviews their clinical, patophysiological and immunological features.

Generator sites for spontaneous activity in neuromyotonia. An EMG study

A 16-year-old female patient with symptoms and signs compatible with neuromyotonia was studied with various neurophysiological tests and with muscle biopsy. Nerve conduction studies revealed signs of axonal motor neuropathy. EMG showed denervation in distal muscles, and moderate neurogenic changes in other muscles. Abundant spontaneous motor unit activity was recorded in all muscles. This activity did not disappear upon proximal nerve blockade with local anaesthetics. Based on the shape of spontaneous discharges and their behaviour on nerve stimulation and during voluntary effort, the site of generation was suggested. This varied for different discharges, from proximally in the nerve, to various sites along the intramuscular nerve tree. In some axons there were signs of conduction block proximal to the generation site for the spontaneous discharges. Different axons showed various degrees of abnormality; local hyperexcitability triggering new impulses only after the passage of a preceding impulse, increased hyperexcitability generating spontaneous activity, total impulse blocking, and finally axonal degeneration. Treatment with dihydantoin reduced the spontaneous activity with concomitant clinical improvement.

Sensitization of Lewis rats with sulfoglucuronosyl paragloboside: electrophysiological and immunological studies of an animal model of peripheral neuropathy

Antibodies against sulfoglucuronosyl glycosphingolipids (SGGLs) are known to be present in sera of patients with chronic polyneuropathy associated with IgM paraproteinemia. We recently studied rats sensitized with sulfoglucuronosyl paragloboside (SGPG), a major SGGL species, emulsified with keyhold limpet hemocyanin and Freund's adjuvant. The titer of the IgM class antibodies against SGPG increased up to 1:1,600, while that of the IgG class increased up to 1:800 2 weeks after sensitization. The antibodies showed a high degree of antigenic specificity; no cross-reactivity with other brain glycolipids could be detected. They, however, reacted with human myelin-associated glycoprotein (MAG) by Western blot analysis, but not with rat MAG. These animal models showed minor but clear clinical signs of neuropathy, consisting of mild tail muscle tone loss and walking disabilities. Electrophysiological examination of the sciatic nerves revealed nerve conduction abnormalities which consisted of conduction block and mild decrease in conduction velocity. Thus, our results support the concept that anti-SGPG antibodies may play an important pathogenetic role in this type of chronic neuropathy.

AAEM case report #30: multifocal motor neuropathy

A 73-year-old man with a 16-year history of fasciculations and 15 years of weakness in his right arm was diagnosed with focal motor neuron disease. After 10 years of purely motor symptoms, he developed mild parasthesias although his sensory examination remained normal. Reflexes were reduced or absent in the weak muscles but were normal elsewhere. Nerve conduction was studied in nerves innervating weak muscles and showed severe motor conduction block. Sensory nerve conduction studies were minimally abnormal, showing reduced amplitudes with normal velocities. Based on the clinical picture and the presence of severe motor conduction block, the patient was diagnosed as multifocal motor neuropathy. Treatment with high-dose intravenous immunoglobulin was given with significant improvement in strength and partial resolution of the conduction block. As this case demonstrates, this treatable disorder may occasionally be mistaken for motor neuron disease although the resemblance is only superficial, and it should never be mistaken for amyotrophic lateral sclerosis. Multifocal motor neuropathy is an inflammatory, demyelinating neuropathy which, like chronic inflammatory demyelinating polyneuropathy (CIDP), is probably immune-mediated. It differs from typical CIDP by virtue of a marked predilection for motor axons, a strikingly restricted distribution, and a protracted course. Treatment with high-dose intravenous immunoglobulin is frequently helpful, but other forms of immune manipulation are less effective.

A novel trial design to study the effect of intravenous immunoglobulin in chronic inflammatory demyelinating polyradiculoneuropathy

Using a novel trial design, we prospectively examined the effect of intravenous immunoglobulin in seven patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) in a double-blind, placebo-controlled cross-over study. We suggest that the commonly used manual muscle testing and Rankin scale are not sufficiently sensitive to measure changes in CIDP and should not be used as isolated outcome measures. We propose a timed 10-m walk, the Nine-Hole Peg Test, the Hammersmith Motor Ability Score, and myometry as alternative measures which are valid, reliable and sensitive. Our trial design permitted the measurement of a treatment response in three responders despite different patterns of disability typical of the broad clinical picture seen in CIDP.

Pathological findings in a patient with amyotrophic lateral sclerosis and multifocal motor neuropathy with conduction block

We studied a 53-year-old woman with progressive weakness of the left arm, gradually spreading to the other limbs. Neurological examination revealed a motor neuron syndrome with paresis, fasciculations and atrophy. Electrophysiological studies showed multiple motor conduction blocks. The anti-GM1 IgM titer was elevated. The patient was thought to have a multifocal motor neuropathy. Despite intravenous cyclophosphamide treatment, however, she died with respiratory insufficiency. On postmortem examination, the brachial plexus showed patches of demyelination underlying different areas of motor conduction block. The spinal cord, however, revealed severe neuronal loss in the ventral horn and axonal loss in the corticospinal tract, indicative of amyotrophic lateral sclerosis. Demyelination of peripheral nerves could have been responsible for the other conduction blocks in this patient. The prominent degeneration of motor neurons, however, must also have played a role in the clinical picture. Some patients with the syndrome of a multifocal motor neuropathy may have MND rather than, or in addition to, a demyelinating peripheral motor neuropathy.

Sensory nerve pathology in multifocal motor neuropathy

The nosological status of multifocal motor neuropathy remains controversial. The clinical and electrodiagnostic hallmarks suggest selective motor fiber involvement. In this study, we asked to what extent sensory nerves might be involved pathologically in multifocal motor neuropathy. Examination of sensory nerve biopsy specimens from 11 patients did reveal pathological findings in all, but they were very mild. An increased number of thinly myelinated, large-caliber fibers was the unifying feature common to each specimen. By electron microscopy, each biopsy specimen had thinly myelinated fibers surrounded by minor onion bulbs. Active demyelination, though scant, was seen in 3 nerves. Myelinated fiber density was normal. Subperineurial edema and inflammation were not present. We conclude that multifocal motor neuropathy is not an exclusively motor abnormality, although it appears to be so clinically and electrophysiologically. The frequent, albeit mild, pathological abnormalities in sensory fibers suggest that the demyelinating pathophysiology also affects sensory fibers, but to a lesser degree than motor fibers. Some investigators maintain that multifocal motor neuropathy is within the spectrum of chronic inflammatory demyelinating polyneuropathy. The very mild degree of sensory fiber involvement, the absence of inflammation or edema, and the distinctive clinical features support the concept of multifocal motor neuropathy as distinct from chronic inflammatory demyelinating polyneuropathy.

Diagnosis in neuromuscular diseases

The diagnosis of neuromuscular diseases can be challenging and successful in the majority of patients, due to advancements in electrophysiology, muscle and nerve biopsy immunohistochemistry, and cytogenetics. This article reviews diverse topics, highlighting these recent achievements, with an emphasis on how they affect the clinical and laboratory diagnosis of specific neuromuscular disorders.

Laboratory testing in peripheral nerve disease

Selecting appropriate laboratory tests in diagnosing peripheral neuropathies is important because it increases the yield of correct diagnoses and is cost effective. A large number of tests are available. This article provides a guide to selecting appropriate tests and reviews the clinical situations that suggest specific tests. Electrodiagnostic testing is valuable in almost all patients with peripheral neuropathy. Quantitative sensory testing adds additional information and is especially useful in patients with small fiber neuropathy. On occasion, routine blood tests may discover metabolic disorders causing a patient's neurologic disorder. A number of antibody assays for neuropathies are available commercially, with the most useful being anti-MAG, anti-GM1, anti-GQ1b, anti-Hu, and anticalcium channel antibodies, but only in very select situations and not as "screening studies". The role of cutaneous nerve and skin biopsies in selected disorders is discussed.

Multifocal motor neuropathy with conduction block: a study of 24 patients

Twenty four patients with pure motor neuropathy are reported. The chronic motor involvement associated with fasciculations and cramps, mainly in the arms, led, in most patients, to an initial diagnosis of motor neuron disease. In some patients (nine of 24), there was no appreciable muscle atrophy. Tendon reflexes were often absent or weak. The finding of persistent multifocal conduction block confined to motor nerve fibres raises questions about the nature and the importance of this syndrome. Segmental reduction of motor conduction velocity occurred at the site of the block, but significant slowing of motor nerve conduction was not found outside this site. The response to intravenous IVIg treatment seems to be correlated with the absence of amyotrophy. Patients with little or no amyotrophy had an initial and sustained response to IVIg, and did not develop amyotrophy during the follow up study. They could be considered to have a variant of chronic inflammatory demyelinating polyneuropathy. Patients with pronounced amyotrophy independent of the disease duration did not respond as well to IVIg treatment, suggesting the existence of a distinct entity. Among the patients treated about two thirds who had an initial good response to IVIg had high or significant antiganglioside GM1 (anti-GM1) antibody titres, but there was no correlation between the high titres before treatment and long lasting response to IVIg treatment.

Chronic motor neuropathies: diagnosis, therapy, and pathogenesis

Pure motor neuropathy syndromes resemble amyotrophic lateral sclerosis variants with no upper motor neuron signs. Their identification is important, as, in contrast to amyotrophic lateral sclerosis, they are often immune mediated and treatable. Typically the immune-mediated motor neuropathy syndromes are distal and asymmetrical and progress slowly. The clinical features may help alert the clinician to the diagnosis, but other ancillary evidence such as abnormalities on electrophysiological testing and the presence of serum autoantibodies to neural antigens are helpful in making the diagnosis more secure. Electrophysiological abnormalities include not only motor conduction block but also other evidence of a demyelinative process such as prolonged distal latencies or F-wave abnormalities. High-titer anti-GM1 antibodies occur frequently but more specific patterns of reactivity may be especially helpful. Treatment of these motor neuropathy syndromes includes cyclophosphamide, which we use in combination with plasma exchange, and in some patients, human immune globulin. Clinical responses to therapy may occur within the first 2 to 4 months in patients with motor neuropathy syndromes with demyelinative features, but only become obvious 6 months or later after starting treatment in patients with predominantly axonal disorders.

Antiglycolipid antibodies in peripheral neuropathy: fact or fiction?

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Human immunoglobulin treatment of multifocal motor neuropathy and polyneuropathy associated with monoclonal gammopathy

Intravenous human immune globulin (IVIg) has been proposed for the treatment of various peripheral neuropathies that are considered to be immunemediated. The results are reported of an open trial conducted in multifocal motor neuropathy and polyneuropathy associated with monoclonal gammopathy. Six cases with multifocal motor neuropathy, selected on clinical and electrophysiological criteria (four of six patients also had significantly high anti-GM1 titres), received IVIg monthly, at doses varying from 1.6 to 2.5 mg/kg, over three to 13 months. The initial response to treatment was dramatic in 3/6 cases (with improvement of at least two grades on the MRC scale in the five more severely affected muscles). The final evaluation showed a good result in 4/6 cases, but the conduction blocks were not significantly reduced. In 13 other cases with polyneuropathy associated with IgM monoclonal gammopathy of unknown significance, IVIg was of benefit, with improvement of at least one grade on the Prineas score, in 4/7 cases previously treated with immunosuppression and 2/3 cases not treated before IVIg. In the last group of four patients with polyneuropathy and IgG monoclonal gammopathy, IVIg was followed by clinical improvement in the two cases with a chronic demyelinating polyneuropathy.

Central nervous system involvement in multifocal demyelinating neuropathy with persistent conduction block

We report the case of a 27-year-old man treated for bilateral optic neuritis 5 and 3 years before who within a few months developed sensorimotor disorders of the arms and legs characterized by asymmetric distribution and distal prominence. In addition to sensorimotor defects, which were particularly marked in the left arm and right leg, clinical examination showed nearly generalized areflexia. Electrophysiological studies revealed a multifocal neuropathy with persistent distal and proximal conduction blocks associated with a considerable slowing of motor nerve conduction, as well as central nervous system involvement indicated by motor-, somatosensory-, and visual-evoked potentials. CSF analysis showed a mildly elevated protein level; anti-GM1 activity was negative. Sural nerve biopsy revealed onion-bulb-like formations, and cerebral MRI showed a small, isolated, and aspecific high signal for white matter. First described by Lewis and Sumner in 1982, multifocal neuropathy with persistent conduction blocks may be associated with central demyelination. Our case is compared with 3 similar ones in the literature, and the favorable effects of steroid therapy are emphasized.

Fasciculation potentials in foot and leg muscles of healthy young adults

The occurrence of fasciculation potentials (FPs) was studied in healthy subjects aged 18-25. In 25 males and 25 females 3 intrinsic foot muscles, the tibialis anterior and the gastrocnemius muscles on both sides were monitored with surface electrodes for 2 min periods. Only potentials with a peak-to-peak amplitude of at least 50 microV were counted. The number of FPs per minute (FPs/min) was significantly higher in the abductor hallucis (AH) and significantly lower in the tibialis anterior as compared to all other muscles (P < 0.001). Men had significantly more FPs in the AH than women (P < 0.05). In all subjects FPs were found in at least 1 AH. Cooling of the foot did not influence the numbers of FPs/min in the foot muscles. To study diurnal variation, all 5 muscles on both sides were monitored 3 times/day on 10 different days in another 10 subjects (5 males, 5 females). Only in the tibialis anterior did the number of FPs never exceed 3/min. In the other muscles considerable fluctuations were found, especially in the AH, where more than 100 FPs/min were occasionally recorded. In the course of the day a significant (P = 0.05) decrease in FPs/min was found for the AH muscle. In 8 subjects there was a significant correlation between the numbers of FPs in the left and right AH during successive recordings. This indicates that an, as yet unknown, general factor determines the fluctuations in numbers of FPs.

Cloning of human anti-GM1 antibodies from motor neuropathy patients

Patients with multifocal motor neuropathy frequently have elevated titers of serum antibodies reactive with GM1 ganglioside. Although these antibodies may cause the syndrome, this has yet to be proven directly. As part of our studies on the nature and pathogenic potential of anti-GM1 antibodies, we have cloned B cells from the peripheral blood of 3 patients with multifocal motor neuropathy and generated four stable heterohybridoma cell lines secreting human monoclonal IgM anti-GM1 antibodies. In this report we describe the basic properties of these monoclonal antibodies in comparison with the patient's sera from which they were derived. The antibodies all differ in their pattern of reactivity with GM1 and other Gal(beta 1-3)GalNAc-containing glycoconjugates. They have widely varying thermal ranges and their reactivities are strongly influenced by the presence of accessory lipids. Affinity purification of the patient's sera with GM1 led to the identification of previously unrecognized paraproteins that were resolvable above the background of polyclonal anti-GM1 IgM. Our data demonstrate considerable heterogeneity in the immune response to GM1 both within individual sera and between different patients, which is likely to be of importance to their role in disease pathogenesis.

AAEM case report #5: Amyotrophic lateral sclerosis

A 40-year-old man presented with a gradual onset of gait unsteadiness and weakness in the arms. The stretch reflexes were normal in the upper extremities but hyperactive in the lower extremities with bilateral Babinski signs. A myelogram revealed a partial obstruction at C-5-6. Two prior electromyograms, 7 and 5 months prior to admission, reportedly showed positive waves only in two peroneal supplied muscles. Repeat electromyographic testing demonstrated normal nerve conduction velocities and needle electrode abnormalities in upper and lower extremities as well as thoracic paraspinal muscles allowing a diagnosis of amyotrophic lateral sclerosis (ALS). The importance of electromyographic testing in clinically nonaffected areas is stressed as well as its role in patients presenting with upper motor neuron signs. It is the task of the clinical electromyographer to consider other entities in the differential diagnosis, such as a multifocal motor neuropathy with conduction blocks and design the tests accordingly. The role of electromyography in the prediction of the course of ALS by assessing the degree of reinnervation is discussed. This will become increasingly important in the design of treatment trials.

Multifocal motor neuropathy: electrodiagnostic features

Diagnosis of multifocal motor neuropathy (MMN), a syndrome characterized by progressive asymmetric weakness with intact sensation, is important because the disorder often responds to treatment. Multifocal partial motor conduction block (PMCB) has been emphasized as a cardinal feature in the diagnosis of this syndrome, but detailed nerve conduction studies are not available. Nine patients, ages 28-58, had chronic, progressive, asymmetric, predominantly distal limb weakness for 5-18 years. Sensation was normal and reflexes were reduced asymmetrically. Although all 9 demonstrated PMCB localized to short nerve segments, additional features of multifocal motor demyelination were present, including temporal dispersion (5 patients), segmentally reduced motor nerve conduction velocity (7 patients), prolonged distal motor latency (4 patients), and prolonged F-wave latency (9 patients). The strength of all patients improved after treatment with human immune globulin. A reduction in the degree of PMCB or an increase in the distal motor amplitude or both accompanied the clinical improvement. These studies suggest that patients with MMN demonstrate widespread evidence of motor demyelination in addition to the well-described PMCB, and that reduction of PMCB accounts for the increase in strength following therapy.