Clinical and electrophysiologic correlates of elevated anti-GM1 antibody titers

We reviewed the clinical and electrophysiologic features of 36 patients with increased titers of IgM anti-GM1 antibodies. Mildly elevated titers of up to 3,200 were not associated with any particular clinical syndrome or disease. Clinically, 14 of 16 patients with highly elevated titers of 6,400 or higher had progressive weakness with lower motor neuron signs; six had active tendon reflexes and eight had absent reflexes, but none had definite upper motor neuron signs. Electrophysiologic studies showed spontaneous activity in all 14 patients, one or more motor conduction blocks in nine, slowed motor conductions in one, and normal conductions in four patients. None had abnormal sensory conductions. These patients presented with a syndrome that has features of, but is distinct from, both motor neuron disease and demyelinating neuropathy.