Immunosuppressive treatment in multifocal motor neuropathy

T cell-dependent activity of ganglioside GM1-specific B cells in Guillain-Barré syndrome and multifocal motor neuropathy in vitro

Synthesis of anti-ganglioside GM1 antibodies of the IgM class by peripheral blood mononuclear cells (PBMNC) from patients with immune-mediated neuropathies and motor neuron diseases and from normal controls was stimulated by Pokeweed mitogen (PWM) in vitro. In patients with acute Guillain-Barré syndrome or multifocal motor neuropathy and high serum titers of IgM anti-ganglioside GM1 antibodies this culture response was greatly enhanced as compared to controls and already detectable in unstimulated cultures. Limiting dilution analysis demonstrated high frequencies of GM1-specific B cells in these patients. Anti-ganglioside GM1 antibodies of the IgG and IgA class were only produced by PBMNC from patients with Guillain-Barré syndrome corresponding to serum titers. In cultures taken at intervals over 6 months in vitro B cell activity for IgM, IgG and IgA anti-ganglioside GM1 antibodies in two Guillain-Barré syndrome patients declined accompanied by clinical improvement and falling serum titers. We conclude that GM1-specific PWM-responsive B cells pre-exist in peripheral blood and respond to T cell-dependent stimulation in Guillain-Barré syndrome and multifocal motor neuropathy.

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.

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.

Chlorambucil fails to improve patients with motor neuropathies and antibodies to gangliosides

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