Variation in performance of the EMG examination at six European laboratories.

The quality of the EMG examination might be improved by standardization. However, knowledge about interlaboratory differences in the performance of the EMG examination is a prerequisite for standardization. The aim of this study was to describe differences in EMG techniques used and number of muscles and nerves examined per patient at 6 European EMG laboratories. The EMG results of 595 patients were prospectively sampled. The average number of muscles examined per patient in different disorders varied from laboratory to laboratory, for example from 3.0 to 10.8 muscles in anterior horn cell disorders and from 2.0 to 5.5 muscles in myopathies. The average number of muscles examined by quantitative EMG varied from 0 to 4.3 in anterior horn cell disorders and from 0.0 to 4.5 in myopathies. Also the average number of nerve segments examined per patient varied from laboratory for example from 2.7 to 17.7 for motor segments and from 3.1 to 9.0 for sensory segments in polyneuropathies. The laboratories that used needle electrodes for nerve conduction studies and quantitative analysis of individual motor unit potentials examined a smaller number of muscles and nerves than laboratories using surface electrodes for nerve conduction studies and qualitative EMG studies. The results of this study may have impact on guidelines and examination protocols as well as on quality assurance.