Electrically Active Immune-mediated Rippling Muscle Disease Preceding Breast Cancer

Abstract

Rippling muscle disease (RMD) is a rare disorder of muscle hyperexcitability clinically characterized by painful muscle stiffness, rippling phenomenon, percussion-induced muscle mounding, and rapid contraction. RMD is typically considered to be electrically silent, but electrical activity during the muscle rippling has been occasionally described. RMD could be genetically determined or immune-mediated (iRMD). The association between cancer and iRMD is extremely rare. We present here a patient with electrically active iRMD preceding the diagnosis of breast cancer. The patient had acetylcholine receptor binding antibodies but no clinical or electrophysiological signs of myasthenia. Muscle biopsy revealed inflammatory changes and a mosaic distribution of sarcolemmal caveolin-3 deficiency. Sequencing of caveolin-3 gene detected no mutation. Immunotherapy led to the resolution of the RMD and disappearance of the serum acetylcholine receptor antibodies. The abnormal electrical activity in this patient suggests that an acquired neuromuscular hyperexcitability syndrome represents a continuum of disorders. The close temporal relationship between the onset of iRMD and the diagnosis of breast cancer raises the possibility that iRMD might be paraneoplastic.