Sensitivity and specificity of single-fibre EMG in the diagnosis of ocular myasthenia varies accordingly to clinical presentation

Maria Pia Giannoccaro, Vitantonio Di Stasi, Corrado Zenesini, Vincenzo Donadio, Patrizia Avoni, Rocco Liguori

Research output: Contribution to journalArticle

Abstract

Background and purpose: Single-fibre electromyography (SF-EMG) is considered as the most sensitive test for the diagnosis of MG. However, previous studies had limitations, such as a retrospective design, non-consecutive sampling, incorporation bias or were performed in small or mixed populations. Our aims were to determine the diagnostic sensitivity and specificity of SF-EMG of the orbicularis oculi in OMG and the utility of this test in relation to patients’ clinical presentation. Materials and methods: We studied 232 consecutive patients referred to the SF-EMG laboratory for a suspected OMG. Stimulated SF-EMG was performed on the orbicularis oculi muscle. Results: OMG was diagnosed in 165 cases and other disorders (OD) in 67. SF-EMG showed a sensitivity of 0.79 (95% CI 0.73–0.85) and a specificity of 0.80 (95% CI 0.71–0.90). False negative results were associated with mild symptoms and with isolated diplopia. Comparison of the diagnostic yield among patients with different clinical presentations showed a similar diagnostic accuracy of SF-EMG in patients with ptosis and in patients with ptosis and diplopia, significantly higher than in patients with isolated diplopia (P < 0.0001). Twenty-two patients with OMG presenting with isolated ptosis or diplopia, who initially tested negative, were re-tested in relation to a worsening of their symptoms showing a positivisation in 91% of cases. Conclusions: SF-EMG on the orbicularis oculi muscle is very sensitive in patients with ptosis. In contrast, in patients with isolated diplopia SF-EMG does not exclude OMG. Therefore, the interpretation of the results of the test should take into account the patients’ clinical presentation.

Original languageEnglish
JournalJournal of Neurology
DOIs
Publication statusE-pub ahead of print - Jan 1 2019

Keywords

  • Ocular myasthenia
  • Orbicularis oculi muscle
  • Sensitivity
  • SF-EMG
  • Specificity

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology

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