Myasthenia, thymoma, presynaptic antibodies, and a continuum of neuromuscular hyperexcitability

To the Editor:

Vernino et al.1 have confirmed our original observations of an association of rippling muscles with myasthenia gravis,2 but have misquoted us. We did not record repetitive motor unit discharges during rippling muscles when our patient was originally seen.

It is difficult to characterize the electrical activity reported in the paper by Vernino et al. at the gain and sweep settings shown in figure 3. A more specific description of the activity reported during the rippling, including size, shape, duration, frequency, and reproducibility of the potentials would be helpful. Could some of this be electrode movement artifact during the rippling phenomena?

My patient with autoimmune rippling muscles was seen quite early in the course of his illness (1 month after the onset of his rippling). Eighteen months later, he was seen at another institution where the neuromuscular specialists also reported his rippling muscles to be “electrically silent.”3 When he returned several years later with florid myasthenia gravis and a thymoma, he did have spontaneous activity on his EMG (fibs, positive waves, etc.) with inflammatory changes on muscle biopsy, but he was no longer rippling.

The cases of autoimmune rippling muscles reported by Müller-Felber et al.4,5 were also seen shortly after the onset of their rippling. Myotonia or motor unit action potentials (MUAPs) were not …