SFEMG: A piece in the diagnostic puzzle of myasthenia

We very much thank Haran (2014) for his comments on our paper. We completely agree that interpretation of the results coming from a diagnostic test must be done with great caution and that only a comprehensive evaluation of the clinical picture and instrumental results will lead to correct diagnosis and proper management of our patients. This is always true, especially in a treatable disease such as myasthenia. Our view is clearly expressed in the very last sentence of the manuscript: “The results of SFEMG should not be interpreted in isolation from the clinical presentation and ancillary test results” (Padua et al., 2014); however, Haran’s reply gives us the opportunity to emphasize the concept even more, which is also the subject of a recent editorial (Caliandro et al., 2013). We know that myasthenia may be difficult to diagnose in individual cases and that we must use all available tools to reach the correct diagnosis (Caliandro et al., 2009), as Haran and coworkers did with their patient (Haran et al., 2013) who, although rare, is a paradigmatic myasthenic patient with antibodies to muscle-specific tyrosine kinase (MuSK-MG) (Evoli et al., 2003 and Evoli et al., 2012). In our work on the reliability of SFEMG in diagnosing myasthenia gravis, we concluded that patients with normal findings at SFEMG are unlikely to be affected by myasthenia gravis because the results from the sensitivity analysis underline that the positive likelihood ratio is always low in both evaluations and therefore, SFEMG has a small value as the confirmatory test for myasthenia gravis diagnosis. Meanwhile, the negative likelihood ratio, although with a wide range, has a low value in both analyses and, therefore, SFEMG has a moderate-to-large value as the test useful in identifying healthy subjects. All this means that normal findings at SFEMG are more meaningful than pathological findings, but of course, a normal SFEMG does not definitively exclude the diagnosis of myasthenia gravis.