18. Is there a P18 component after stimulation of the median nerve at the wrist?

Abstract

cussion-induced rippling of the anterior thigh muscles and biceps brachii. Creatine kinase (CK) values were elevated 3-fold and acetylcholine receptor (AChR) binding antibodies were positive. Nerve conduction studies, including 2 Hz repetitive nerve stimulation were normal. Single fiber electromyography was normal. The needle examination demonstrated small motor unit potentials. Multichannel, intramuscular needle recording of thigh muscles revealed a brief discharge with a frequency of 100 Hz lasting 0.5–1 s. These discharges were much briefer than muscle rippling noted on the skin surface. Muscle biopsy showed an active inflammatory myopathy and reduced sarcolemmal caveolin-3 immunostain in a mosaic pattern. Caveolin-3 gene analysis revealed no mutation. Immunotherapy resulted in resolution of the muscle weakness and rippling and normalization of the CK and AChR antibodies. Conclusion: This case underscores the importance of caveolin-3 in the pathogenesis of iRMD. In addition, the abnormal muscle activity was not completely silent in this patient, suggesting that acquired neuromuscular hyperexcitability consists of a continuum of disorders.