Abstract
IntroductionDifferentiating between functional jerks (FJ) and organic myoclonus can be challenging. At present, the only advanced diagnostic biomarker to support FJ is the Bereitschaftspotential (BP). However, its sensitivity is limited and its evaluation subjective. Recently, event related desynchronisation in the broad beta range (13–45 Hz) prior to functional generalised axial (propriospinal) myoclonus was reported as a possible complementary diagnostic marker for FJ. Here we study the value of ERD together with a quantified BP in clinical practice. MethodsTwenty-nine patients with FJ and 16 patients with cortical myoclonus (CM) were included. Jerk-locked back-averaging for determination of the ‘classical’ and quantified BP, and time-frequency decomposition for the event related desynchronisation (ERD) were performed. Diagnostic gain, sensitivity and specificity were obtained for individual and combined techniques. ResultsWe detected a classical BP in 14/29, a quantitative BP in 15/29 and an ERD in 18/29 patients. At group level we demonstrate that ERD in the broad beta band preceding a jerk has significantly higher amplitude in FJ compared to CM (respectively −0.14 ± 0.13 and +0.04 ± 0.09 (p < 0.001)). Adding ERD to the classical BP achieved an additional diagnostic gain of 53%. Furthermore, when combining ERD with quantified and classical BP, an additional diagnostic gain of 71% was achieved without loss of specificity. ConclusionBased on the current findings we propose to the use of combined beta ERD assessment and quantitative BP analyses in patients with a clinical suspicion for all types of FJ with a negative classical BP.
Highlights
Differentiating between functional jerks (FJ) and organic myoclonus can be challenging
FJ are clinically characterized by an Abbreviations: BP, Bereitschaftspotential; CM, cortical myoclonus; event related desynchronisation (ERD), Event Related Desynchronisation; FJ, functional jerks
No significant correlation was present between the number of jerks and ERD amplitude in either the CM or FJ group
Summary
Differentiating between functional jerks (FJ) and organic myoclonus can be challenging. Event related desynchronisation in the broad beta range (13e45 Hz) prior to functional generalised axial (propriospinal) myoclonus was reported as a possible complementary diagnostic marker for FJ. When combining ERD with quantified and classical BP, an additional diagnostic gain of 71% was achieved without loss of specificity. Conclusion: Based on the current findings we propose to the use of combined beta ERD assessment and quantitative BP analyses in patients with a clinical suspicion for all types of FJ with a negative classical BP. FJ are clinically characterized by an Abbreviations: BP, Bereitschaftspotential; CM, cortical myoclonus; ERD, Event Related Desynchronisation; FJ, functional jerks. The reported sensitivity of a positive BP in FJ is heterogeneous ranging from 25% [18] to more than 80% in selected cohorts [9,23] This emphasizes the importance to improve the electrophysiological biomarkers in FJ
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