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Giant Somatosensory Evoked Potentials Coincident With Epileptiform Discharges in Acutely Comatose Patients

  • David A. Houlden (a1), Mark I. Boulos (a2), Brian J. Murray (a2), Loretta Norton (a3) and G. Bryan Young (a3)...

Abstract

Background

The amplitude of the cortically generated somatosensory evoked potential (SSEP) is used to predict outcome in comatose patients. The relationship between epileptiform discharges and SSEP amplitude has not been elucidated in those patients.

Methods

Bilateral median nerve SSEP and electroencephalograph (EEG) studies were performed in a comatose patient (patient 1) 1 day after cardiac surgery and repeated 4 days later. He had tranexamic acid administered before and during surgery. Another comatose patient (patient 2) had the same studies performed 1 day after sustaining 10 minutes of pulseless electrical cardiac activity.

Results

Both comatose patients had epileptiform discharges (on EEG) that were coincident with giant cortically generated SSEPs. In patient 1, the EEG and SSEP studies repeated 5 days postoperatively showed no epileptiform discharges, and the cortically generated SSEP amplitude was decreased (normalized) compared with that obtained one day postoperatively. He emerged from coma and had a good recovery. Patient 2 died shortly after EEG and SSEP testing.

Conclusions

Epileptiform discharges were associated with giant cortically generated median nerve SSEP amplitude (tranexamic acid was implicated in patient 1 and anoxic brain injury in patient 2). Accordingly, those who use the amplitude of cortically generated SSEPs for predicting outcome in comatose patients should consider the presence of epileptiform discharges (detected by EEG) as a potential confounding factor.

Des PES géants coïncidant avec des décharges épileptiformes chez des patients en coma aigu. Contexte: L’amplitude des potentiels évoqués somesthésiques (PES) générés par le cortex est utilisée pour prédire l’issue chez les patients comateux. La relation entre les décharges épileptiformes et l’amplitude des PES n’a pas été élucidée chez ces patients. Méthode: Nous avons effectué des études des PES des deux nerfs médians et de l’électroencéphalogramme chez un premier patient comateux le lendemain d’une chirurgie cardiaque et nous avons répété ces examens 4 jours plus tard. Il avait reçu de l’acide tranexamique avant et pendant la chirurgie. Un deuxième patient comateux a subi les mêmes examens le lendemain d’un épisode de 10 minutes d’activité électrique cardiaque sans pouls. Résultats: Les deux patients comateux présentaient des décharges épileptiformes à l’ÉEG, qui coïncidaient avec des PES géants générés par le cortex. Chez le premier patient, aucune décharge épileptiforme n’a été enregistrée à l’ÉEG et aux PES répétés 5 jours après la chirurgie et l’amplitude des PES générés par le cortex était diminuée (normalisée) par rapport à ce qui avait été enregistré le lendemain de la chirurgie. Il a repris conscience et il s’est rétabli. Le deuxième patient est décédé peu après que l’ÉEG et les PES aient été enregistrés. Conclusions: Les décharges épileptiformes étaient associées à une amplitude géante des PES du nerf médian générés au cortex (l’acide tranexaminique était en cause chez le premier patient et les séquelles de l’anoxie cérébrale chez le deuxième patient). Par conséquent, ceux qui utilisent l’amplitude des PES générés par le cortex pour prédire l’issue chez les patients comateux devraient prendre tenir compte du fait que la présence de décharges épileptiformes (détectées à l’ÉEG) peut être un facteur de confusion.

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Copyright

Corresponding author

Correspondence to: David Houlden, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, ON K1Y 4E9, Canada Email: dhoulden@toh.on.ca

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