Neuromyotonia: autoimmune pathogenesis and response to immune modulating therapy

Background: Neuromyotonia (NMT) has been postulated to be an autoimmune cha nnelopathy, probably by affecting voltage gated potassium channels (VGKC) l eading to excitation and abnormal discharges [Sinha et al., Lancet 338 (199 1) 75]. Objective: To report three patients with NMT who had other associat ed immune-mediated conditions, i.e., myasthenia gravis, thymoma and various types of peripheral neuropathies. One patient had peripheral neuropathy an d involvement of pre- and post-synaptic neuromuscular junction. Results: Al l three patients had evidence of polyneuropathy and neuromyotonic discharge s on electrodiagnostic studies. Elevated acetylcholine receptor antibodies were noted in all patients and malignant thymoma was found in two patients with metastasis. All three patients showed moderate to marked response to p lasma exchange. Conclusions: These findings strongly suggest a humoral auto immune pathogenesis of NMT, probably by K+ channel involvement, affecting a cetylcholine quantal release and postsynaptic membrane. Clinicians should b e aware of this: association of immune-mediated conditions in NMT patients and marked improvement with plasma exchange. (C) 2000 Elsevier Science B.V. All rights reserved.