- Email: [email protected]
Reply to Nunes and Khan
Letters to the Editor / Clinical Neurophysiology 116 (2005) 2859–2862
2861
Reply to Nunes and Khan
Fig. 1. Polysomnographic record, speed 15 mm/s, of a 6 days old, term, female newborn, with refractory seizures since the first day of life. We can observe among the suppression period silent EEG seizures on the right occipital region.
(the EEG of this patient was illustrated as Fig. 1 on the same article). Previous to our report, other researchers, as Lombroso (1994) had shown similar pattern of silent or clinical seizures during the suppression period of a BS neonatal EEG. We suggest that the conclusions of this case report should be reviewed as silent EEG seizures can be recorded in analog EEG.
References Al-Futaisi A, Banwell B, Ochi A, Hew J, Chu B, Oishi M, Otsubo H. Hidden focal EEG seizures during prolonged suppressions and highamplitude bursts in early infantile epileptic encephalopathy. Clin Neurophysiol 2005;116:1113–7. Lombroso CT. Neonatal EEG and polygraphy. In: Niedermeyer E, Lopes da Silva F, editors. Electroencephalography. 3rd ed. Baltimore: Urban & Schwarzenberg; 1994. p. 803–75. Nunes ML, Giraldes MM, Pinho AP, da Costa JC. Prognostic value of non reactive burst suppression EEG pattern associated to early neonatal seizures. Arq Neuropsiquiatr 2005;63:14–9.
Magda Lahorgue Nunesa Richard Lester Khanb a Department of Neurology and Pediatrics, PUCRS School of Medicine, Porto Alegre, RS, Brazil b Clinical Neurophysiology Laboratory, Hospital Sa˜o Lucas PUCRS, Porto Alegre, Rs, Brazil. E-mail addresses: [email protected], [email protected]
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.07.023
My collaborators and I appreciate your letter disputing our assertion that our paper, “Hidden focal EEG seizures during prolonged suppressions and high-amplitude bursts in early infantile epileptic encephalopathy,” was the first to report clinically silent seizures made possible by using digital EEG technology. To demonstrate, you cited your recent publication on the “Prognostic value of nonreactive burst suppression EEG pattern associated to early neonatal seizures” and Lomboso’s chapter “Neonatal EEG and polygraphy” in the third edition of Electroencephalography. In your paper you described clinically silent (subclinical) or clinical seizures during suppression periods using analog EEG. Analog EEG captured the clinically silent electrographical seizures in 4 of 12 patients with EIEE or early myoclonic encephalopathy (EME). Figure 1 showed a gradual buildup of rhythmic seizures during the suppression period. In contrast, our paper with digital EEG showing hidden focal EEG seizures during prolonged suppression and high amplitude bursts described very low amplitude EEG seizures compared to the interictal extremely high amplitude bursts. Table 1 illustrated the extreme amplitude difference. At 8 months of age, the patient’s EEG seizures reached a maximum of 30 mV compared to interictal bursts of 1000 mV, or one thirtieth the size. Figure 1 in your paper, however, showed the maximum amplitude, which occurred toward the end of the seizures, as reaching one-half the amplitude of the interictal bursts that were visible on the left side of the figure. We wish to emphasize that these very low amplitude seizures occurring among suppression-burst patterns were “hidden.” Without using digital EEG to expand the extremely high amplitude bursts, the very low amplitude seizures in this patient would not have been visible. The clinically silent seizures in our paper were not only subclinical seizures but also hidden, very low amplitude seizures. Digital EEG recording allowed us to alter the sensitivity, filters, and montages in an off-line retrospective analysis. When we did not observe clinical seizures, we were able to take advantages of these capabilities of digital EEG. The retrospective analysis using higher sensitivities revealed hidden EEG seizures which aided us in treating the patient. We were able to look beyond the high amplitude waves and see the very low amplitude, sustained and focal EEG seizures. The clinical seizures became obvious, and interictal bursts appeared at lower amplitude and had shorter interburst periods. As reported by Ohtahara and Yamatogi interictal bursts usually reached 150–350 mV (Ohtahara and Yamatogi 2003; Yamatogi and Ohtahara 2002). In fact, Dr. Ohtahara commented to us that high amplitude bursts in this patient were quite unusual for patients with EIEE. We agree that some silent EEG seizures may be detectable with analog EEG, as you have demonstrated. However, we
2862
Letters to the Editor / Clinical Neurophysiology 116 (2005) 2859–2862
suggest that you try digital EEGs for your patients, including the neonates, because we expect that you will more frequently collect hidden, very low amplitude and focal EEG seizures than you do with analog EEG. Furthermore, we would appreciate your further study that analyzes the appearances of interictal bursts between clinically silent EEG seizures and electroclinical seizures. You may see that the interictal bursts become more frequent while focal EEG seizures appear infrequently or disappear because of the reverse interrelationship between interictal and ictal discharges.
Yamatogi Y, Ohtahara S. Early-infantile epileptic encephalopathy with suppression-bursts, Ohtahara syndrome; its overview referring to our 16 cases. Brain Dev 2002;24(1):13–23.
Hiroshi Otsubo Amna Al-Futaisi The Hospital for Sick Children, Department of Neurology, 555 University Avenue, M5G1X8 Toronto, Ont., Canada E-mail address: [email protected]
References Ohtahara S, Yamatogi Y. Epileptic encephalopathies in early infancy with suppression-burst. J Clin Neurophysiol 2003;20:398–407.
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.08.025
2861
Reply to Nunes and Khan
Fig. 1. Polysomnographic record, speed 15 mm/s, of a 6 days old, term, female newborn, with refractory seizures since the first day of life. We can observe among the suppression period silent EEG seizures on the right occipital region.
(the EEG of this patient was illustrated as Fig. 1 on the same article). Previous to our report, other researchers, as Lombroso (1994) had shown similar pattern of silent or clinical seizures during the suppression period of a BS neonatal EEG. We suggest that the conclusions of this case report should be reviewed as silent EEG seizures can be recorded in analog EEG.
References Al-Futaisi A, Banwell B, Ochi A, Hew J, Chu B, Oishi M, Otsubo H. Hidden focal EEG seizures during prolonged suppressions and highamplitude bursts in early infantile epileptic encephalopathy. Clin Neurophysiol 2005;116:1113–7. Lombroso CT. Neonatal EEG and polygraphy. In: Niedermeyer E, Lopes da Silva F, editors. Electroencephalography. 3rd ed. Baltimore: Urban & Schwarzenberg; 1994. p. 803–75. Nunes ML, Giraldes MM, Pinho AP, da Costa JC. Prognostic value of non reactive burst suppression EEG pattern associated to early neonatal seizures. Arq Neuropsiquiatr 2005;63:14–9.
Magda Lahorgue Nunesa Richard Lester Khanb a Department of Neurology and Pediatrics, PUCRS School of Medicine, Porto Alegre, RS, Brazil b Clinical Neurophysiology Laboratory, Hospital Sa˜o Lucas PUCRS, Porto Alegre, Rs, Brazil. E-mail addresses: [email protected], [email protected]
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.07.023
My collaborators and I appreciate your letter disputing our assertion that our paper, “Hidden focal EEG seizures during prolonged suppressions and high-amplitude bursts in early infantile epileptic encephalopathy,” was the first to report clinically silent seizures made possible by using digital EEG technology. To demonstrate, you cited your recent publication on the “Prognostic value of nonreactive burst suppression EEG pattern associated to early neonatal seizures” and Lomboso’s chapter “Neonatal EEG and polygraphy” in the third edition of Electroencephalography. In your paper you described clinically silent (subclinical) or clinical seizures during suppression periods using analog EEG. Analog EEG captured the clinically silent electrographical seizures in 4 of 12 patients with EIEE or early myoclonic encephalopathy (EME). Figure 1 showed a gradual buildup of rhythmic seizures during the suppression period. In contrast, our paper with digital EEG showing hidden focal EEG seizures during prolonged suppression and high amplitude bursts described very low amplitude EEG seizures compared to the interictal extremely high amplitude bursts. Table 1 illustrated the extreme amplitude difference. At 8 months of age, the patient’s EEG seizures reached a maximum of 30 mV compared to interictal bursts of 1000 mV, or one thirtieth the size. Figure 1 in your paper, however, showed the maximum amplitude, which occurred toward the end of the seizures, as reaching one-half the amplitude of the interictal bursts that were visible on the left side of the figure. We wish to emphasize that these very low amplitude seizures occurring among suppression-burst patterns were “hidden.” Without using digital EEG to expand the extremely high amplitude bursts, the very low amplitude seizures in this patient would not have been visible. The clinically silent seizures in our paper were not only subclinical seizures but also hidden, very low amplitude seizures. Digital EEG recording allowed us to alter the sensitivity, filters, and montages in an off-line retrospective analysis. When we did not observe clinical seizures, we were able to take advantages of these capabilities of digital EEG. The retrospective analysis using higher sensitivities revealed hidden EEG seizures which aided us in treating the patient. We were able to look beyond the high amplitude waves and see the very low amplitude, sustained and focal EEG seizures. The clinical seizures became obvious, and interictal bursts appeared at lower amplitude and had shorter interburst periods. As reported by Ohtahara and Yamatogi interictal bursts usually reached 150–350 mV (Ohtahara and Yamatogi 2003; Yamatogi and Ohtahara 2002). In fact, Dr. Ohtahara commented to us that high amplitude bursts in this patient were quite unusual for patients with EIEE. We agree that some silent EEG seizures may be detectable with analog EEG, as you have demonstrated. However, we
2862
Letters to the Editor / Clinical Neurophysiology 116 (2005) 2859–2862
suggest that you try digital EEGs for your patients, including the neonates, because we expect that you will more frequently collect hidden, very low amplitude and focal EEG seizures than you do with analog EEG. Furthermore, we would appreciate your further study that analyzes the appearances of interictal bursts between clinically silent EEG seizures and electroclinical seizures. You may see that the interictal bursts become more frequent while focal EEG seizures appear infrequently or disappear because of the reverse interrelationship between interictal and ictal discharges.
Yamatogi Y, Ohtahara S. Early-infantile epileptic encephalopathy with suppression-bursts, Ohtahara syndrome; its overview referring to our 16 cases. Brain Dev 2002;24(1):13–23.
Hiroshi Otsubo Amna Al-Futaisi The Hospital for Sick Children, Department of Neurology, 555 University Avenue, M5G1X8 Toronto, Ont., Canada E-mail address: [email protected]
References Ohtahara S, Yamatogi Y. Epileptic encephalopathies in early infancy with suppression-burst. J Clin Neurophysiol 2003;20:398–407.
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.08.025