Multifocal acquired demyelinating neuropathy masquerading as motor neuron disease

Fasciculation-myokymic activity and prolonged nerve conduction block. A physiopathological relationship in radiation-induced brachial plexopathy

Fourteen radiation-induced brachial plexus neuropathies in 12 patients suffering from cancer were studied. Neurophysiological evaluation showed a diffuse neurogenic lesion with muscular denervation signs associated with motor and sensory nerve conduction impairment of axonal type in the distal segments of the arm. Somatosensory evoked potentials were frequently abnormal, with absence of N9 in 9 out of the 10 extremities explored. The most characteristic findings were, however, the presence of fasciculation potentials--single and grouped--and myokymic discharges in 78.5% of cases (11 out of 14 plexuses), and a motor nerve conduction block on proximal stimulation, at the supraclavicular as well as cervical spine levels, in all of the cases. Both phenomena showed a high correlation when analyzed in the same neuromuscular territory. The 5 muscles with no voluntary activity and complete--or nearly complete--motor nerve conduction block were the ones with the most intense ectopic activities. The conduction blocks were present after long periods of illness in all cases and, in 2 of the cases, they persisted in successive explorations at intervals of 9 months and 2 years respectively. These data would support a probable cause-effect relationship between a persistent and prolonged motor nerve conduction block and the presence of fasciculation-myokymic type activities. One could even postulate that the infrequent neuropathies, in which both findings have been described as relevant features, have a similar physiopathological mechanism.

Motor neuron disease: a disease of old age

There is little information dealing specifically with motor neuron disease (MND) in the elderly. Given current epidemiological trends, geriatricians will be increasingly called upon to diagnose and manage this condition. We report four patients who presented within a six month period to a geriatric medical unit, and place this experience in the perspective of 229 patients from a population-based study of adult-onset MND in Scotland in 1989 and 1990. In 1990 Scotland had a crude annual incidence of MND of 2.25/100,000; the figure for those over 65 is four times greater. MND is more common in men, but the sex ratio was nearly equal over the age of 65. The risk of presenting with bulbar palsy was greater in women, and even higher in elderly women. This, together with increasing age, is the most important negative prognostic factor in MND. Problems with the diagnosis and management of MND in the elderly are highlighted.

Persistent and transient "conduction block" in motor neuron diseases

Although conduction block indicates dysfunction of peripheral nerve, it may occur in patients with clinically typical motor neuron disease. There are no universally accepted criteria to identify conduction block, so diagnosis may be difficult. In some peripheral neuropathies, conduction block persists over long periods of time. If conduction block persists in motor neuron disease, then a more reproducible means for identification would be available. We repeatedly studied 9 patients with different forms of motor neuron diseases; conduction block was suspected because of excessive loss of the amplitude of motor evoked responses between distal and proximal stimulation sites. Five showed persistent amplitude loss at intervals between 12 and 36 months. All had focal loss of amplitude and area across a specific segment; all were men; none had definite upper motor neuron signs, 2 had probable and 3 had no upper motor neuron signs; 1 had IgM paraproteinemia, one elevated anti-GM1 titers; the duration of symptoms spanned 4-13 years. Four patients had transient loss of amplitude that was not reproduced in intervals between 3 and 13 months. None had focal loss of both amplitude and area; 2 were men; all had definite upper motor neuron signs and none had symptoms for more than 3-13 months; and none had immunological abnormalities. Thus, patients with persistent amplitude loss fulfill other criteria for conduction block, have prolonged survival but otherwise have clinical syndromes indistinguishable from ALS, except that definite upper motor neuron signs seem to be exceptional.

Conduction abnormalities induced by sera of patients with multifocal motor neuropathy and anti-GM1 antibodies

Increased titers of anti-GM1 antibodies have been associated with motor neuron disease and motor neuropathy with or without conduction block. To investigate the pathogenetic role of anti-GM1 antibodies we injected into rat tibial nerves sera from patients with multifocal motor neuropathy and conduction block (MMN) or progressive spinal muscular atrophy (PMA), both presenting anti-GM1 antibodies. Sera of patients with MMN produced reduction of amplitude and dispersion of compound muscle action potential from proximal stimulation. Morphometry revealed demyelination in 6.2% of fibers. Sera of patients with PMA did not produce clear-cut electrophysiological or morphological changes. Differential effects of sera from patients presenting high-titer anti-GM1 antibodies, but with distinct clinical syndromes, might depend on differences in anti-GM1 antibody affinity, valency, or ability to fix complement. Alternatively, circulating factors other than, or in addition to, anti-GM1 antibodies present in sera of patients with MMN, but not of PMA patients, might be responsible for conduction abnormalities and reproduce them after passive transfer.

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

Detection of conduction block (CB) has important clinical implications because it suggests segmental demyelination potentially reversible following treatment. There are no universally accepted criteria to define CB. We tested the sensitivity of two diagnostic criteria of partial motor CB in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and hereditary motor-sensory neuropathy type I (HMSN I) which are thought to be the prototypes of segmental and uniform demyelination respectively. Criterion I requires > 20% drop in negative peak amplitude and area and < 15% change in duration between proximal and distal compound muscle action potentials (CMAPs). Criterion II requires > 50% drop in negative peak amplitude and area of proximal CMAP independently from temporal dispersion. Twenty-eight percent of CIDP nerves and 65% of CIDP patients had CB according to criterion I. However, 29% of nerves and 61% of patients with HMSN I also fulfilled the same criterion. Thirty-four percent of CIDP nerves and 78% of CIDP patients and none of HMSN I patients fulfilled criterion II. Criterion II has the same sensitivity as criterion I, but seems to be highly specific in diagnosis of the segmental demyelination characteristic of CIDP. Therefore this criterion should be employed, as the diagnostic tool of CB, in chronic neuropathies presenting high stimulation threshold and coexisting axonal loss.

Multifocal motor neuropathy: response to human immune globulin

Multifocal motor neuropathy (MMN) is a progressive disorder producing asymmetrical weakness and muscle wasting. Case reports suggest that patients with MMN improve after cyclophosphamide therapy, but not after prednisone or plasmapheresis. Because MMN is likely to be immune mediated, we investigated the therapeutic response to human immune globulin (HIG) in an open, uncontrolled trial. Nine patients, ages 28 to 58 years, had chronic, progressive, asymmetrical, predominantly distal, limb weakness for 5 to 18 years. Sensation was normal, and reflexes were reduced asymmetrically. All had physiological evidence of multifocal motor demyelination with partial motor conduction block, and 7 had elevated serum titers of anti-GM1 IgM antibody. All patients were treated with HIG, 1.6 to 2.4 gm/kg, given intravenously over 3 to 5 days. Strength improved in all patients 3 to 10 days after treatment, with improvement peaking at 2 weeks and lasting for an average of 2 months. The range of functional improvement varied from dramatic to mild. The degree of partial motor conduction block was reduced, at least partially, in 7 of 8 patients. The serum anti-GM1 antibody titers did not change. Repeated courses of HIG resulted in similar improvements. We conclude that HIG may be an effective therapy for patients with MMN.

Pathological findings at the site of conduction block in multifocal motor neuropathy

We report on 2 patients with multifocal motor neuropathy with focal conduction block involving motor but not sensory fibers at the site of nerve swelling. A nerve biopsy specimen from adjacent to the enlargement in 1 patient showed a perivascular area containing scattered demyelinated axons surrounded by small onion bulbs. The observed pathological findings are consistent with the conduction block considered characteristic of this neuropathy, although the underlying immunological mechanisms for selectivity and persistence remain undetermined.

Cortical excitability in amyotrophic lateral sclerosis: a clue to pathogenesis

Motor evoked potentials (MEPs) were recorded from selected non-wasted, non-denervated hand muscles in 40 patients with Amyotrophic Lateral Sclerosis (ALS) with both upper and lower motor neuron signs. In most the compound muscle action potential (CMAP) of the target muscle was normal. Compared to the control group, cortical threshold in ALS varied considerably and there was a significant (r2 = 0.702) inverse, exponential, correlation between cortical threshold and MEP/CMAP ratio. There was a linear correlation between threshold and disease duration (r2 = 0.66) so that early in the disease threshold was normal and later the motor cortex could not be stimulated. It is suggested that early in ALS normal threshold reflects glutamate-induced hyper-excitability of the corticomotoneuron. The findings lend support to the hypothesis that ALS is primarily a disease of the corticomotoneuron.

Multifocal motor nerve conduction abnormalities in amyotrophic lateral sclerosis

Motor nerve conduction in motor neuron disease is considered normal until the terminal stages of the disease, a notable exception being lower motor neuron syndrome associated with anti-glycolipid antibodies. We reviewed the electrophysiological findings in all our patients who were diagnosed as having amyotrophic lateral sclerosis (ALS) during the last 6 years. Six patients, clinically indistinguishable from "classical" ALS patients, out of 31 (19%) displayed motor nerve conduction abnormalities. The most consistent finding, occurring in all 6, was prolonged distal latency or reduced conduction velocity in the distal segment of the median nerve, with normal sensory conduction, suggesting possible pressure proneness of motor nerve fibers in ALS. Additional abnormalities included multifocal motor conduction slowing (3 patients), and conduction blocks (4 patients). None of the patients had paraproteinemia and anti-GM1 and anti-GD1a antibodies were not detected. Thus, a subgroup of clinically indistinguishable ALS patients may have multifocal motor nerve conduction abnormalities, indicating motor nerve fiber involvement. The etiology and pathogenesis of the peripheral nerve involvement are presently unknown.

Comparison of electric and magnetic coil stimulation in the supraclavicular region

We compared the compound motor action potentials (CMAPs) evoked in the biceps, triceps, and abductor digiti minimi (ADM) muscles by conventional electrical stimulation at Erb's point (EP), and by magnetic coil stimulation of the supraclavicular region in 11 normal subjects. We found that magnetic coil stimulation was less effective than conventional stimulation in activating motor fibers in the brachial plexus in 45% of the recordings analyzed. CMAP amplitudes greater than those obtained with EP electrical stimulation were seen in 16% of recordings with supraclavicular magnetic stimulation, and in 33% of recordings with cervical magnetic stimulation, indicating that EP electrical stimulation is submaximal in a large proportion of cases.

Amyotrophic lateral sclerosis (ALS): a phylogenetic disease of the corticomotoneuron?

It is proposed that the primary cell involved in amyotrophic lateral sclerosis (ALS) is the corticomotoneuron. The spinal motoneuron becomes affected as a result of antegrade effects. This hypothesis does not negate most of the presently popular theories regarding the pathogenesis of ALS, but directs focus to one cell type--the corticomotoneuron. It takes cognizance of the complex, monosynaptic, corticomotoneuronal-spinomotoneuronal connections that have evolved in primates, and especially in man. It might explain the lack of any natural or thus far induced animal model which closely mimics the human disease. Threshold measurements to transcotical magnetic stimulation might be used to test the hypothesis. Replication of ALS in an animal is only likely to succeed in a nonhuman primate.

Chronic multifocal demyelinating neuropathy associated with central nervous system demyelination

We have carried out a long-term study of lesions found in a man who had a demyelinating disease of both central and peripheral nervous systems. During the 10 years of his clinical course, he suffered from optic neuritis, multifocal myelitis, and chronic multifocal demyelinating neuropathy, with persistent conduction block. Our study revealed that both central and peripheral nervous system demyelination occurred repeatedly and simultaneously.

Invited review: motor neuropathies, motor neuron disorders, and antiglycolipid antibodies

High titers of IgM anti-GM1 antibodies are commonly found in the serum of patients with some lower motor neuron disorders and peripheral neuropathies. Enzyme-linked immunosorbent assays (ELISA) are useful for the detection and quantitation of anti-GM1 antibodies. Testing for serum anti-GM1 activity is indicated in the diagnostic evaluation of lower motor neuron syndromes. The presence of high titers of anti-GM1 antibodies mandates careful electrophysiologic testing for the motor conduction block that is found in multifocal motor neuropathy, a treatable disorder. Quantitation of anti-GM1 antibodies may also be a useful guide in the treatment of multifocal motor neuropathy. Further study of antiglycolipid antibodies in motor neuron disorders and peripheral neuropathies may provide clues to the events that stimulate these antibodies and to the pathogenesis of such syndromes.

Immunosuppressive treatment in multifocal motor neuropathy

We report the results of immunosuppressive treatments of 13 patients with multifocal motor neuropathy and elevated titers of serum antibodies to the GM1 ganglioside. All patients failed to respond to oral prednisone. There was no clinical response in 4 patients treated with plasma exchange. Nine patients received cyclophosphamide, with clinical improvement and fall in antibody titers in 8. In 3 patients, cyclophosphamide was discontinued with ensuing clinical relapse and rise in the titers of serum anti-GM1 antibodies. These patients provide further evidence for the efficacy of cyclophosphamide therapy in patients with multifocal motor neuropathy.

Chronic acquired demyelinating motor neuropathy

A patient with chronic, acquired, demyelinating, pure or predominantly motor asymmetric neuropathy is described. Electrophysiological tests showed multifocal conduction block in motor nerves. The sensory system was intact and the first signs of slight trival involvement appeared after 4 years of disease duration. The antiganglioside antibodies were present in serum and the patient responded to immunosuppressive therapy (azathioprine). Distinction of such cases from motor neuron disease is critical since motor demyelinating neuropathy is treatable in most cases.

Predictive value of anti-GM1 ganglioside antibodies in neuromuscular diseases: a study of 180 sera

The incidence of anti-GM1 antibodies in the serum of 104 patients with neurological diseases, 35 patients with non-neurological diseases (NND) and 41 normal controls was determined by enzyme-linked immunosorbent assay (ELISA). Anti-GM1 antibodies were found in 90% of patients presenting with a motor neuropathy (all except one had multifocal conduction blocks). A large proportion (60%) of these patients displayed high antibody titer ranging from 101 to 788. A low incidence of anti-GM1 antibodies was found in the other groups of patients, i.e. 21% of amyotrophic lateral sclerosis (ALS), 26% of other neurological diseases (OND) and 23% of NND. High antibody titers ranging from 106 to 260 were found in two (5%) ALS patients, one (2%) OND patient (myasthenia gravis), and one (3%) NND patient (Waldenström's disease). This study shows that high titers of anti-GM1 antibodies are found in a large proportion of patients with motor neuropathy with multifocal conduction blocks. This argues for a possible autoimmune origin of this neuropathy. We suggest that anti-GM1 antibody determination should be included systematically in the evaluation of all patients with motor neuron diseases and predominantly motor neuropathies.

Chronic multifocal demyelinating neuropathy simulating motor neuron disease

We describe a patient with a chronic acquired predominantly motor polyneuropathy. His clinical picture initially led to a diagnosis of lower motor neuron form of amyotrophic lateral sclerosis. However electrophysiological examination revealed multifocal, prevalently proximal, conduction blocks at sites not prone to compression. Distinguishing this unusual polyneuropathy from motor neuron diseases is critical, since the former is a potentially, treatable disorder.

AAEM minimonograph #34: polyneuropathy: classification by nerve conduction studies and electromyography

Electrodiagnostic evaluation of patients with suspected polyneuropathy is useful for detecting and documenting peripheral abnormalities, identifying the predominant pathophysiology, and determining the prognosis for certain disorders. The electrodiagnostic classification of polyneuropathy is associated with morphologic correlates and is based upon determining involvement of sensory and motor fibers and distinguishing between predominantly axon loss and demyelinating lesions. Accurate electrodiagnostic classification leads to a more focused and expedient identification of the etiology of polyneuropathy in clinical situations.

Lower motor neuron syndromes defined by patterns of weakness, nerve conduction abnormalities, and high titers of antiglycolipid antibodies

We studied 74 patients with progressive, asymmetrical lower motor neuron syndromes. Clinical features of these patients, including age, sex, disease duration, patterns of weakness, and reflex changes, were evaluated by review of records. In each patient the clinical features were compared to the type of nerve conduction abnormalities and to the specificities of high-titer serum antiglycolipid antibodies. Antibody specificities were determined by an enzyme-linked immunosorbent assay using purified glycolipids and carbohydrates as substrates. Our results show that high titers of antibodies to glycolipids are common in sera of patients with lower motor neuron syndromes. Selective patterns of reactivity indicate that specific carbohydrate epitopes on the glycolipids are the targets of the high-titer antibodies in individual patients with lower motor neuron syndromes. Several distinct lower motor neuron syndromes can be identified based on clinical, physiological, and antiglycolipid antibody characteristics. These syndromes include multifocal motor neuropathy with evidence of multifocal conduction block on motor, but not sensory, axons and frequent (84%) high titers of anti-GM1 ganglioside antibodies; a lower motor neuron syndrome with predominantly distal weakness early in the disease course, no conduction block, and a high incidence (64%) of anti-GM1 antibodies; and a lower motor neuron syndrome with predominant early weakness in proximal muscles and serum antibodies to asialo-GM1 that do not cross-react with GM1 ganglioside.

The idiopathic polyradiculoneuropathies: a historical guide to an understanding of the clinical syndromes

Recognition of the idiopathic polyradiculoneuropathies began with Graves, Landry and Dumenil who, respectively, suggested, implied and established the peripheral nervous system as a site of disease. Over the ensuing decades other neurologists separated the idiopathic disorders from neuropathies of known cause, poliomyelitis and myelopathies. Guillain, Barré and Strohl described the acute benign syndrome and its cerebrospinal fluid abnormalities. Haymaker & Kernohan solidified the features of the acute disorder as did Dyck et al and Prineas & McLeod for the relapsing and chronic conditions. Currently the idiopathic polyradiculoneuropathies are regarded as autoimmune in nature, clinically generalized with some cases having focal involvement, and of varying severity with only occasional fatalities. Neurologists are divided as to whether the acute and chronic disorders represent 2 different conditions or whether they are 2 forms in the spectrum of a single disorder. This author favors the concept of a single disorder with multifarious manifestations.

Neuropathy with onion bulb formations and pure motor manifestations

A thirty-eight-year-old man presented with a six year history of symptoms resembling an anterior horn cell disorder. There was progressive upper extremity wasting and weakness in the absence of sensory complaints. Electrophysiologic abnormalities were confined to motor nerve conduction and indicated a demyelinating process involving the brachial plexus and major proximal upper extremity nerve trucks bilaterally. Biopsy of the proximal right ulnar nerve revealed changes suggesting a chronic demyelinating process, and onion-bulb formations were present. Immunohistochemical staining for S-100 protein was positive in the cells comprising the onion-bulbs, indicating a Schwann cell, not a perineurial origin of these cells. After 8 years, symptoms have failed to appear in the lower limbs. Recent reports in the literature have begun to delineate the syndrome, which appears to represent an unusual, localized or multifocal, sometimes inflammatory, clinically benign neuropathy that can mimic motor neuron disease in its earlier stages. We report the first such case with underlying pathology.

A treatable multifocal motor neuropathy with antibodies to GM1 ganglioside

We report 2 patients with a treatable, immune-mediated motor polyneuropathy associated with antibodies to defined neural antigens. In these patients asymmetrical weakness developed in one arm and progressed over 2 to 3 years to involve the other arm, legs, and trunk. Both patients were initially diagnosed as having lower motor neuron forms of amyotrophic lateral sclerosis. However, repeated electrophysiological testing eventually showed multifocal conduction blocks in motor but not sensory fibers compatible with patchy selective demyelination. Serum testing by thin-layer chromatography and enzyme-linked immunosorbent assay revealed that both patients had high titers of antibody directed against GM1 and other gangliosides. Initial therapeutic trials of prednisone (100 mg daily for 4 to 6 months) and plasmapheresis were unsuccessful. Treatment with cyclophosphamide, however, was followed by marked improvement in strength in both patients.