Acquired Rippling Muscle Disease with Acetylcholine Receptor Antibodies (P1-8.008)

Abstract

<h3>Objective:</h3> To report a case series of acquired rippling muscle disease (RMD) with acetylcholine receptor (AChR) antibodies. <h3>Background:</h3> Previous studies have demonstrated association of acquired RMD with autoimmune disorders, or less commonly with cancer. AChR antibodies are often observed in RMD in parallel with the presumed immune-mediated etiology of acquired RMD. Despite having AChR antibodies, acquired RMD patients may exhibit minimal or no manifestations of myasthenia gravis (MG). Treatment selection in these RMD patients may prove challenging. <h3>Design/Methods:</h3> All cases of acquired RMD seen at our institution since 2010 were identified by search of the electronic medical record. <h3>Results:</h3> Three patients with acquired RMD were identified. These were men with classic RMD symptoms beginning in the fourth to sixth decade. Two developed ocular MG after onset of RMD, while the third had no MG symptoms. None had other autoimmune disorders or malignancy. AChR-binding antibodies were detected in all three patients, and two had positive striational antibodies. None had thymoma. Creatine kinase was mildly elevated, and caveolin-3 genetic testing was negative in all three patients. Concentric needle electromyography showed electrical silence during spontaneous muscle contractions in 2 of 3 patients. The third patient exhibited decreased caveolin-3 and dystrophin sarcolemmal immunoreactivity on muscle biopsy. All patients received at least one immunosuppressive (IS) therapy. While MG symptoms responded to IS treatment, RMD symptoms were more refractory. Only one individual who received intravenous immunoglobulin (IVIg) experienced significant improvement in RMD symptoms. Symptomatic treatment for RMD yielded only minimal benefit. <h3>Conclusions:</h3> Acquired RMD is a rare disorder of muscular hyperexcitability, presumably related to an underlying immune-mediated phenomenon. Most cases of RMD/MG were heralded by RMD and may only exhibit minimal or no manifestations of MG despite AChR antibody positivity. IS therapies appear to be ineffective for RMD symptoms, although one patient had significant symptomatic benefit with IVIg. <b>Disclosure:</b> Dr. Wannarong has nothing to disclose. Dr. Gable has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Medscape, Web MD. Dr. Gable has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Pharmacy Times. Dr. Gable has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Cowen. Dr. Gable has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Argenx. Dr. Gable has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Ultragenx. Dr. Gable has received personal compensation in the range of $5,000-$9,999 for serving as a Lecture series with Medscape. Dr. Juel has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Immunovant. Dr. Juel has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Alexion. Dr. Juel has received personal compensation in the range of $0-$499 for serving on a Scientific Advisory or Data Safety Monitoring board for Accordant Health Services. The institution of Dr. Juel has received research support from argenx. The institution of Dr. Juel has received research support from Alexion. The institution of Dr. Juel has received research support from Janssen. The institution of Dr. Juel has received research support from NIH Rare Diseases Network.