Neuromuscular transmission defects in myopathies: Rare but worth searching for

Introduction: Decremental responses in repetitive nerve stimulation have been reported in a few hereditary myopathies. We examined the frequency of decrement in a cohort of myopathy patients. Methods: We reviewed all patients referred for myopathy who underwent repetitive nerve stimulation between January 2007 and May 2017. We included patients with decrement (>10%) and either a pathological or molecular diagnosis of myopathy. Results: Among 157 patients with myopathies, 4 patients had decrement (2 hydroxychloroquine-associated vacuolar myopathy, 1 centronuclear myopathy, and 1 distal myopathy). One hydroxychloroquine-associated vacuolar myopathy patient also had inflammatory myopathy. Pyridostigmine improved weakness in the centronuclear myopathy patient, but not in the distal myopathy patient. No patient with an acquired myopathy received pyridostigmine. Conclusions: Despite the rare occurrence of decrement in myopathy, its presence may urge consideration of pharmacological intervention. Muscle Nerve 59:475–478, 2019.