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BRIEF COMMUNICATIONS: M. C. Durand, H. Prigent, V. Sivadon–Tardy, D. Orlikowski, C. Caudie, C. Devaux, B. Clair, J. -L. Gaillard, F. Lofaso, J. -C. Raphael, and T. Sharshar Significance of phrenic nerve electrophysiological abnormalities in Guillain–Barré syndrome Neurology 2005; 65: 1646-1649 [Abstract] [Full text] [PDF]

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Significance of phrenic nerve electrophysiological abnormalities in Guillain–Barré syndrome

Charles F. Bolton   (29 March 2006)

Reply from the authors

Tarek Sharshar, Frédéric Lofaso, MD, PhD, Garches, France   (29 March 2006)

Significance of phrenic nerve electrophysiological abnormalities in Guillain–Barré syndrome 29 March 2006
Charles F. Bolton, Queen's University Etherington Hall, Room 3008, Queen's University, Kingston, Ontario, K7L 3N6, Canada Send Correspondence to journal: Re: Significance of phrenic nerve electrophysiological abnormalities in Guillain–Barré syndrome cb41{at}post.queensu.ca Charles F. Bolton	The prospective study of Guillain-Barré syndrome (GBS) by Durand et al [1] concluded that the latency and amplitude measurements of phrenic nerve conduction were only weakly correlated with forced vital capacity (FVC), and were similar in ventilated and nonventilated patients. Considering the limitation of the techniques they utilized, we agree that such techniques would be of little benefit in determining the need for mechanical ventilation. However, neurologists, clinical neurophysiologists and intensivists should know that the well documented techniques of phrenic nerve conduction and needle EMG of the diaphragm [3] are beneficial. The authors compared their results with our earlier report in which both phrenic nerve conduction and needle EMG of the diaphragm were utilized. [4] We studied 40 patients in the early stages of GBS according to a set protocol. The need for mechanical ventilation correlated with reduction of the diaphragm compound muscle action potential amplitude (P =0.005) and negative peak area (P = 0.001), and abnormal needle EMG studies of the diaphragm (P = 0.013). While these measurements also correlated with FVC, FVC was abnormal on the day of the EMG in only 13 of 16 ventilated patients. Five patients had normal electrophysiological studies, none requiring mechanical ventilation. Thus, carefully performed phrenic nerve conduction [2] and needle EMG of the diaphragm [3] are complementary, providing important information on axonal degeneration and segmental demyelination of the phrenic nerves, and denervation and re-innervation of the diaphragm. This information is valuable, along with non-electrophysiological methods such as FVC, in determining the need for mechanical ventilation and also valuable in follow-up studies, especially in attempted weaning from the ventilator. There may be apprehension that needle EMG of the diaphragm may be complicated by pneumothorax. However, among 1000 persons only two had a pneumothorax. Both had chronic obstructive lung disease and were on a ventilator. We now recognize that this was contraindicating the procedure. [5] Respiratory electrophysiological studies should be performed routinely in conjunction with limb studies within two weeks of onset of GBS, at six weeks and six months or more often, especially before attempted weaning from the ventilator. References 1. Durand MC, Prigent H, Sivadon-Tardy V, et al. Significance of phrenic nerve electrophysiological abnormalities in Guillain-Barré sundrome. Neurology 2005;65:1646-1649. 2. Chen R, Collins S, Remtulla H, Parkes A, Bolton CF. Phrenic nerve conduction study in normal subjects. Muscle Nerve 1995;18:330-335. 3. Bolton CF, Grand’Maison F, Parkes A, Shrkum M. Needle electromyography of the diaphragm. Muscle Nerve 1992;15:678-681. 4. Zifko U, Chen R, Remtulla H, Hahn AF, Koopman W, Bolton CF. Respiratory electrophysiological studies in Guillain-Barré syndrome. Journal of Neurology, Neurosurgery and Psychiatry 1996;60:191-194. 5. Bolton CF, Chen R, Wijdicks EFM, Zifko UA. Neurology of breathing. Philadelphia, PA: Butterworth-Heinemann (Elsevier), 2004:84. Disclosure: The author reports no conflicts of interest.
Reply from the authors 29 March 2006
Tarek Sharshar, Hôpital Raymond Poincaré Service de Réanimation,104 Boulevard Raymond Poincaré 92380 Garches France, Frédéric Lofaso, MD, PhD, Garches, France Send Correspondence to journal: Re: Reply from the authors tarek.sharshar{at}rpc.ap-hop-paris.fr Tarek Sharshar, et al.	We thank Bolton for his interest in our paper. The main result of our study [1] was that the assessment of phrenic nerve latency and diaphragm compound motor action potential (CMAP) at the time of admission in patients with Guillain-Barré syndrome (GBS) did not predict subsequent respiratory failure. We elected to use a technique (i.e. recording from surface electrodes) available in routine clinical practice. In contrast to the measurement of phrenic nerve latency and diaphragm CMAP with surface electrodes, diaphragm needle EMG is not performed routinely in most centers. Even if it is reported to be rarely complicated by pneumothorax, such a complication is more likely to occur if the neurophysiologist is not familiar with the technique. It must also be noted that needle EMG signal can also be contaminated by the activity of adjacent muscles [6]thus reducing its benefit. Although Zifko and collaborators [4] have found that needle EMG was more frequently abnormal in the GBS patient who had developed respiratory failure, they did not assess whether it was more predictive than vital capacity (VC). VC remains--along with inability to lift the head, bulbar dysfunction and a delay from the onset of symptoms to admission of less than seven days--the most powerful predictor of respiratory deterioration. [7,8] It would of interest to determine whether phrenic nerve electrophysiology is helpful in discriminating patients at risk of prolonged mechanical ventilation. Currently, we do not repeat standard and phrenic nerve electrophysiology and usually start weaning when the VC exceeds 30% predicted and muscle strength begins to improve. We proceed to extubation when the patient is able to breathe spontaneously on T-tube for at least for 6 hours. Strategies that would improve the anticipation of respiratory failure and predict the need for prolonged mechanical ventilation in GBS would be desirable. We believe that electrophysiology may be helpful but its usefulness needs to be properly studied in comparison with established clinical parameters which can be assessed quickly and easily. References 6. Hodges PW, Gandevia SC. Pitfalls of intramuscular electromyographic recordings from the human costal diaphragm. Clin Neurophysiol 2000;111:1420-1424. 7. Lawn ND, Fletcher D, Henderson RD, Wolter TD, Wijdicks EF. Anticipating mechanical ventilation in Guillain-Barre syndrome. Arch Neurol 2001;58:893-898. 8. Sharshar T, Chevret S, Bourdain F, Raphael JC. Early predictors of mechanical ventilation in Guillain-Barre syndrome. Crit Care Med 2003;31:278-283. Disclosure: The authors report no conflicts of interest.