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BRIEF COMMUNICATIONS: G. M. Terwindt, E. E. Kors, A. A. Vein, M. D. Ferrari, and J. G. van Dijk Single-fiber EMG in familial hemiplegic migraine Neurology 2004; 63: 1942-1943 [Abstract] [Full text] [PDF]

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Reply to Shoenen et al

J. Gert van Dijk, Gisela M Terwindt, Esther E. Kors, Alla A Vein, Michel D. Ferrari   (21 January 2005)

Single-fiber EMG in familial hemiplegic migraine

Jean E Schoenen, Anna Ambrosini, Alain Maertens de Noordhout   (21 January 2005)

Reply to Shoenen et al 21 January 2005
J. Gert van Dijk, Leiden University Medical Centre PO Box 9600, 2300 RC Leiden, The Netherlands, Gisela M Terwindt, Esther E. Kors, Alla A Vein, Michel D. Ferrari Send Correspondence to journal: Re: Reply to Shoenen et al j.g.van_dijk.neur{at}lumc.nl J. Gert van Dijk, et al.	Schoenen et al address the implications of our findings as well as methodological matters. We reported normal mean jitter in FHM [1] as customary. [3] We also investigated abnormality on the level of single fibers, but the normal results were omitted due to length limitations set by editorial policy. Schoenen's group reported abnormal SFEMG results in common forms of migraine. A possible dysfunction of P/Q Ca2+ channels was mentioned as the rationale for the study as well as the explanation of the abnormal findings. There was no proof for a mutation affecting this channel in these patients. We felt that the contrast with normal results in FHM patients in whom such a mutation had been proven was remarkable. Schoenen seeks to resolve the contrast by concluding that their findings in common forms of migraine were not due to a dysfunctioning P/Q Ca2+ channel, which leaves the mechanism unclear. We feel justified in stressing that blocking without a high jitter is odd. Past reports on botulism mentioned that blocking can occur in fibers with only mildly abnormal jitter, but there were always fibers with markedly abnormal jitter in these patients [6] not reported in the migraine patients. This observation has not been repeated in more recent papers on botulism. Blocking clearly increased with jitter. [7] Near-liminal stimulation causes axonal blocking, which has nothing to do with the neuromuscular synapse; even then blocks are usually accompanied by high jitter. The only well-documented instance of blocking with normal jitter concerns blocking in abnormal axons in Guillain-Barré syndrome.[8] We consider complete blinding a necessity rather than illusory, as recommended by the American Association of Neuromuscular and Electrodiagnostic Medicine [9] and the STARD initiative. [10] We do not think methodological explanations for the contrast can be ignored. Differences between groups are possible, even though the P/Q Ca2+ channel rationale to presume SFEMG abnormalities in migraine has been disproven. We await confirmation SFEMG studies in common forms of migraine that follow the above-mentioned guidelines. References 6. Girlanda P, Dattola R, Messina C. Single fibre EMG in 6 cases of botulism.Acta Neurol Scand 1983;67:118-123. 7. Padua L, Aprle I, Lo Monaco M, Fenicia F, Pauri F, Tonali P. Neurophysiological assessment in the diagosis of botulism: usefulness of single-fiber EMG. Muscle Nerve 1999; 22: 1388-1392 8. Spaans F, Vredeveld J-W, Morrë HHE, Jacobs BC, de Baets MH. Dysfunction at the motor endplate and axon membrane in Guillain-Barré syndrome: a single-fiber EMG study. Muscle Nerve 2003; 27: 426-434 9. Dubinsky RM, Werner RA, Haig, AJ, Miller RC. Will EDX physicians be left behind? The need for blinded studies to evaluate electrodiagnostic studies as a diagnostic test. A report of the American association of electrodiagnostic medicine task force on blinding research. http://www.aanem.org/aaem/positive_waves/July2003/BlindedStudy.pdf. 10. Bossuyt PM, Reitsma JB. Standards for Reporting of Diagnostic Accuracy. The STARD initiative. Lancet 2003; 361: 71.
Single-fiber EMG in familial hemiplegic migraine 21 January 2005
Jean E Schoenen, University of Liège University Department of Neurology.Headache Research Unit.CHR Citadelle.B-4000 Liège.Belgium., Anna Ambrosini, Alain Maertens de Noordhout Send Correspondence to journal: Re: Single-fiber EMG in familial hemiplegic migraine jschoenen{at}ulg.ac.be Jean E Schoenen, et al.	Terwindt et al [1] stress the importance of methodological factors in single fiber EMG (SFEMG). When we performed the first SFEMG study in migraine [2], we were aware that adequate training was necessary to avoid technical flaws. The statement by Terwindt et al [1] that jitter is pronounced before blocking occurs cannot be generalized. It does not apply to botulism for instance, and may also not apply to migraine. Complete blinding seems illusory in patients with rare conditions who undergo multiple investigations. We chose to limit blinding to the migraine subtype [2] which likely avoided significant bias, as SFEMG abnormalities were found in only 17 out of 62 patients. It surprised us that Terwindt et al (1) found that “the contrast” between our SFEMG report and their normal findings in FHM patients with a proven mutation in the CACNA1A gene “remarkable”. First, there is no disagreement between the two studies. Average mean MCD was within normal limits in all our subgroups of migraineurs. [2] When we reclassified patients according to the 2nd ICHD edition, three fulfilled the criteria for familial hemiplegic migraine, five others for sporadic hemiplegic migraine. Only one patient in each group had an increased mean MCD, which is comparable to Terwindt et al’s results. Second, as recommended in SFEMG guidelines [3] and contrary to Terwindt et al, we took into account single muscle fiber MCD which was increased in 10-15% of fibers in four patients, but in at least one fiber in nine others. Third, although our studies were initiated by the finding of CACNA1A mutations in FHM and the known crucial role of P/Q Ca2+ channels in neuromuscular transmission, we concentrated on the common forms of migraine following the hypothesis that CACNA1A could be involved in other migraine types than FHM. The latter hypothesis, however, has not been confirmed by genetic studies [4] and in migraineurs with abnormal SFEMG our screening for 14 known FHM1 mutations was negative (unpublished results). It seems unlikely that the neuromuscular transmission abnormalities reported by us [2] and by others in subtypes of migraine and in cluster headache [5] are related to dysfunctioning P/Q Ca2+ channels. Although our analysis may have been more sensitive, we think that the contrast between Terwindt et al and our results is not due to methodological factors, but to the study of different migraine types. References 1. Terwindt GM, Kors EE, Vein AA, Ferrari MD, van Dijk JG. Single-fiber EMG in familial hemiplegic migraine. Neurology 2004;63:1942–1943. 2. Ambrosini A, Maertens de Noordhout A, Schoenen J. Neuromuscular transmission in migraine: A single fiber EMG study in clinical subgroups. Neurology 2001;56:1038-1043. 3.Sanders DB, Stalberg EV. AAEM minimonograph #25: single-fiber electromyography. Muscle Nerve 1996;19:1069-1083. 4. Lea RA, Curtain RP, Hutchins C, Brimage PJ, Griffiths LR. Investigation of the CACNA1A gene as a candidate for typical migraine susceptibility. A J Med Genet 2001;105:707-12. 5. Ertas M, Baslo MB. Abnormal neuromuscular transmission in cluster headache. Headache 2003; 43:616-20.