Acquired neuromyotonia and chronic inflammatory demyelinating neuropathies: 3 case reports

Acquired neuromyotonia is a very rare entity of probable autoimmune origin. Its association with chronic inflammatory demyelinating neuropathies is quite rare. We report here three such cases. Two men and one woman between 40 to 56 years old, presented neuromyotonia before, after, or at the time of the onset of a chronic inflammatory demyelinating neuropathy. They reported abnormal muscle twitching, contractures, or muscle hypertrophy in the regions affected by the neuropathy. The neuropathy was responsible for motor deficit and areflexia in all the case and paresthesia in one with a multifocal distribution in all the patients. The level of impairment due to the neuropathy and the neuromyotonia were equivalent. For all of the patients, the electromyogram (EMG) showed spontaneous activities matching the diagnosis criteria of neuromyotonia as well as conduction blocks or temporal dispersion with slowed conduction velocities in two patients. One patient met the diagnostic criteria of multifocal motor neuropathy with conduction blocks, the second one was classified as a Lewis-Sumner syndrome, and the third one remained unclassified. None of the three patients had thymoma or anti-Caspr2 antibodies. For all of them, the neuromyotonia dramatically improved with intravenous immunoglobulins (IVIg) while the neuropathy responded to IVIg in only two patients. The last patient developed a severe motor asymmetrical neuropathy with axonal loss and amyotrophy despite several attempts of immunomodulatory treatments. Conduction blocks and neuromyotonia are assumed to be generated in the nodo-paranodal region. However, the chronological dissociation between the onset of the two disorders suggests that the mechanisms underlying them were not strictly identical while response to IVIg indicates an immune mediated disease. Thus, these three cases are probably due to an autoimmune disturbance affecting several targets in the nodo-paranodal region. The absence of anti-Caspr2 antibodies leads us to suspect the presence of other antibodies not yet identified.