T37. Electrodiagnostic criteria for neuromuscular transmission disorders suggested by a European consensus group

Abstract

Despite advances in antibody testing, electrodiagnostic testing still plays a crucial role in diagnosing disorders of the neuromuscular transmission (NMT). Existing criteria for NMT disorders are derived from consensus, while no evidence-based criteria have been published. The aim of this study was to derive evidence-based criteria for the electrodiagnosis of NMT disorders, supported on clinical diagnosis as agreed by consensus (gold standard) in an expert group. A group of experienced physicians in the European multicentre project ESTEEM representing six different European countries reviewed samples of their patients diagnosed with NMT disorder. A total of 164 examinations obtained a consensus diagnosis of definite (105), probable (44), or possible (15) NMT disorder. In these examinations 405 repetitive nerve stimulation (RNS) and 116 single fibre electromyography (SFEMG) studies were performed. The average numbers of abnormal RNS and SFEMG studies in the patients with a probable consensus diagnosis of NMT disorder served as basis for recommendation of minimal electrodiagnostic criteria. The average number of performed RNS studies per patient from each of eight physicians ranged from 1.9 to 5.2, while the average number of abnormal RNS studies ranged from 0.7 to 3.2. For SFEMG the average number ranged from 0.09 to 1.6 for performed studies and from 0.09 to 1.5 for abnormal studies. In the 99 patients diagnosed with generalised myasthenia, the sensitivity of RNS varied from 43% (abductor digiti minimi muscle) to 78% (nasalis muscle), while the sensitivity of SFEMG ranged from 80% (orbicularis oculi muscle) to 100% (anconeus and frontalis muscles). As minimal electrodiagnostic criteria, the ESTEEM group recommends that either (a) 2 abnormal RNS studies, or (b) 1 abnormal RNS study and 1 abnormal SFEMG study, or (c) 2 abnormal SFEMG should be required to diagnose a NMT disorder. To evaluate the electrodiagnostic tests, the routinely used limits for decrement at the different centres should be applied. Electrodiagnostic consensus recommendations for the minimum number of RNS and SFEMG studies to diagnose disorders of the neuromuscular junction are suggested. The recommendations encourage use of different limits according to the muscle examined and the relevant age group (e.g. children vs. adults), preferably obtained locally at each diagnostic centre. These are the first electrodiagnostic criteria for NMT based on clinical evidence of diagnosis as agreed by consensus.