Immune-Mediated Rippling Muscle Disease: Another Inflammatory Myopathy in Myasthenia Gravis

I read with great interest the article by Suzuki and colleagues¹ on myocarditis and polymyositis in myasthenia gravis (MG). Suzuki et al described 6 patients with MG with polymyositis. Onset of polymyositis was either prior to or at the same time as onset of myasthenic symptoms.¹ Intramuscular lymphocytic infiltration in MG is not uncommon, and it is often interpreted as a coincidental polymyositis.² To date, more than 30 cases of MG-associated polymyositis (MG-PM) have been desribed.² Patients described by Suzuki et al¹ had additional weakness and hyperCKemia, which supports a diagnosis of coexisting polymyositis. However, other patients with MG-PM who had been described earlier often did not have these clinical findings; therefore, a diagnosis of polymyositis may not be accurate.² Presence of endomysial lymphocytic infiltrates is nonspecific and can be seen in either thymoma-associated MG or other inflammatory myopathies.² A certain number of these patients with MG-PM who have subtle or no clinical findings suggestive of polymyositis may in fact represent another uncommon and underrecognized MG-associated inflammatory myopathy, immune-mediated rippling muscle disease (RMD).