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Electroencephalographic patterns in unresponsive pediatric patients
Electroencephalographic Patterns in Unresponsive Pediatric Patients Syed A. Hosain, MD, Gail E. Solomon, MD, and Erik J. Kobylarz, MD, PhD To study the occurrence and incidence of various electroencephalographic patterns, the electroencephalograms of unresponsive pediatric patients admitted to the intensive care unit were analyzed. The interpreters were unaware of the patients’ clinical diagnoses. A total of 178 electroencephalographic studies performed on unresponsive patients were analyzed over a period of 3 years. The mean age of the study patients was 7.9 years. Sixty-six patients were less than 1 year old. The following electroencephalographic patterns were observed: 58 patients (33%) manifested electroencephalographic patterns consistent with nonconvulsive status epilepticus. Of the patients with nonconvulsive status epilepticus, 32 patients (18%) had generalized nonconvulsive status epilepticus and 26 patients (14%) manifested partial nonconvulsive status epilepticus. The remaining 120 patients (67%) manifested diffuse cerebral dysfunction, with the majority having severe diffuse cerebral dysfunction. Only 4 patients (2%) had triphasic waves, suggesting a metabolic encephalopathy. Thirty-six percent of the patients under the age of 1 year had electroencephalographic patterns consistent with nonconvulsive status epilepticus. Nonconvulsive status epilepticus is a relatively common electroencephalographic pattern in unresponsive pediatric patients. Metabolic encephalopathy is uncommon in this patient group. © 2005 by Elsevier Inc. All rights reserved. Hosain SA, Solomon GE, Kobylarz EJ. Electroencephalographic patterns in unresponsive pediatric patients. Pediatr Neurol 2005;32:162-165.
Introduction Determining the etiology of a change in mental status in unresponsive patients can be challenging; electroencepha-
From the Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York.
162
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lography may be extremely helpful in such situations. In fact, this neurophysiologic modality is necessary to diagnose nonconvulsive status epilepticus, which is potentially a treatable condition. Electroencephalography is routinely performed on patients, who after experiencing overt seizures, have persistently altered mental status. In a recent electroencephalographic study of pediatric patients in the emergency department, Alehan et al. found that 5 of 21 patients presenting in the emergency department with altered mental status and acute confusional state were in nonconvulsive status epilepticus as determined by electroencephalography [1]. However, an electroencephalogram is not routinely requested for the evaluation of patients in unresponsive states of undetermined etiology without accompanying obvious clinical signs of seizures. In addition, the incidence of seizures is higher in the first decade of life compared with that for other age groups [2]. Therefore it is necessary to consider status epilepticus as one of the likely etiologies of an altered mental states in children with or without a prior history of seizures. There are two major types of status epilepticus, convulsive and nonconvulsive status epilepticus. Convulsive status epilepticus is an easily recognizable entity. Nonconvulsive status epilepticus is more heterogeneous and controversial in its definition. It is often defined as an epileptic state lasting more than 30 minutes, with seizure activity on electroencephalogram associated with an alteration in mental status [3]. However, nonconvulsive status epilepticus is not easy to recognize clinically, and patients in unresponsive states are frequently suspected of being in nonconvulsive status epilepticus. There are few reports on the electroencephalographic pattern in obtunded or unresponsive pediatric patients. Privitera et al. reported a 37% incidence of nonconvulsive status epilepticus in unresponsive adult patients [4]. However, the incidence of nonconvulsive status epilepticus in unresponsive pediatric patients is unknown. In addition, few large-scale studies of
Communications should be addressed to: Dr. Hosain; Department of Neurology and Neuroscience; Weil-Cornell Medical Center; 525 East 68th Street; Suite K-615; New York, NY 10021. Received February 2, 2004; accepted September 8, 2004.
© 2005 by Elsevier Inc. All rights reserved. doi:10.1016/j.pediatrneurol.2004.09.008 ● 0887-8994/05/$—see front matter
the utility of electroencephalography for the evaluation of patients in unresponsive states without overt signs of seizure activity have been published. We were interested in studying electroencephalographic patterns of unresponsive children and infants without overt seizures. Nonconvulsive status epilepticus can be subdivided into two groups: complex partial status epilepticus with lateralized epileptiform features and generalized nonconvulsive status epilepticus with bilateral synchronous discharges. In this study, the incidence and specific electroencephalographic patterns of nonconvulsive status epilepticus in pediatric patients over a 3-year period were evaluated. Methods All inpatient electroencephalographic studies performed in our hospital over a 3-year period (1999-2001) were retrospectively reviewed. We identified 178 pediatric patients for whom an electroencephalogram was requested owing to the patients’ persistent unresponsiveness. These patients were examined by a pediatric neurologist or intensivists and had neither overt clinical seizures nor pharmacologic agents that could result in an altered mental status. These electroencephalographic studies were requested by intensivists and neurologists for patients admitted to intensive care units. All of the electroencephalographic recordings were performed continuously for 30 minutes using the 10-20 system, following the standard recommendations of the American Electroencephalography Society. All electroencephalograms were interpreted by two independent board certified electroencephalographers. The electroencephalography interpreters were unaware of patients’ actual clinical diagnoses and past medical history. The electroencephalographic patterns in unresponsive patients were classified into two major categories: A. The first pattern was that of nonconvulsive status epilepticus, consisting of one or more of the following: (a) continuous or nearly continuous spike-and-wave discharges; (b) electrographic partial seizures; (c) periodic lateralized epileptiform discharges with runs of evolving epileptiform activity. B. The second category of electroencephalographic findings consisted of: (a) interictal spikes and sharp waves and periodic lateralized epileptiform discharges; (b) diffuse cerebral dysfunction; (c) alpha coma; (d) burst-suppression pattern; (e) triphasic waves.
Table 1.
EEG abnormalities in unresponsive children
EEG Abnormality
Number of Patients*
%
Left hemispheric NCSE Right hemispheric NCSE Generalized NCSE Left PLEDs Right PLEDs Bilateral PLEDs (or BiPEDs) Alpha coma Theta coma Burst suppression Interictal epileptiform activity Diffuse cerebral dysfunction (total) Diffuse cerebral dysfunction (not in NCSE) Triphasic waves
13 13 32 1 3 0 2 0 4 23 149 120 6
7.5 7.5 18 0.6 1.6 0 1 0 2 13 84 67 3
* Includes all patients in the study (n ⫽ 178). Abbreviations: BiPEDs ⫽ Bilateral independent periodic epileptiform discharges EEG ⫽ Electroencephalographic NCSE ⫽ Nonconvulsive status epilepticus PLEDs ⫽ Periodic lateralized epileptiform discharges
in partial nonconvulsive status epilepticus, there was no hemispheral predominance (right ⫽ 13 vs left ⫽ 13). The remaining 120 patients (67%) not in nonconvulsive status epilepticus manifested diffuse cerebral dysfunction, with the majority having severe diffuse cerebral dysfunction. Of the patients with diffuse cerebral dysfunction who were not in nonconvulsive status epilepticus, 22 (12%) manifested interictal epileptiform activity (spikes or sharp waves, or both). Four patients (2%) had periodic lateralized epileptiform discharges, one of whom had an ictal pattern. This individual was the only patient with periodic lateralized epileptiform discharges included in the nonconvulsive status epilepticus group. Two patients (1%) had an alpha coma pattern and four (2%) patients were in nonpharmacologic burst suppression. Only 6 patients (3%) had triphasic waves, suggesting a metabolic encephalopathy.
Results Discussion A total of 178 electroencephalographic studies on unresponsive pediatric patients were identified over a 3-year period. The mean age was 7.9 years (range, 1 day-18 years). Seventy-eight patients (44%) were female, and 100 (56%) were male. Seventy-two patients (40%) were less than 1 year old. The results of the study are summarized in Table 1. Fifty-eight patients (33%) manifested electroencephalographic patterns consistent with nonconvulsive status epilepticus. Thirty-six percent of the patients under the age of 1 year manifested electroencephalographic patterns consistent with nonconvulsive status epilepticus. Of the patients with nonconvulsive status epilepticus, 32 patients (18%) had generalized and 26 patients (15%) had partial nonconvulsive status epilepticus patterns. For the patients
Routine electroencephalograms are typically performed for more than one half hour in duration. Therefore this neurophysiologic study can have a high degree of sensitivity and specificity for identifying nonconvulsive status epilepticus. This study was conducted to identify the causes of unresponsiveness, as well as the incidence of nonconvulsive status epilepticus in pediatric patients. Because there are few comparative pediatric studies, we also compared our results to analogous adult data. Nonconvulsive status epilepticus electroencephalographic patterns were documented in one third of the unresponsive pediatric patients included in this study, which is a surprisingly high percentage. Of the patients less than 1 year of age, even a higher proportion (36%)
Hosain et al: EEG in Unresponsive Children 163
were in nonconvulsive status epilepticus. In a small cohort of patients (n ⫽ 15) Alehan et al. [1] reported a 29% incidence of nonconvulsive status epilepticus as diagnosed by electroencephalography for pediatric patients evaluated in the emergency room setting. The incidence of nonconvulsive status epilepticus in the present study is similar to that reported by Alehan et al. and that reported in an adult study by Privitera et al. [1,4]. In the adult study, Privitera et al. reported that 59 (37%) of 198 patients with altered consciousness (its degree varied from confusion interrupted by seizures to coma) were in a state of nonconvulsive status epilepticus, 23 without evident clinical manifestations and 36 exhibiting subtle motor activity. Their report revealed a slightly higher rate of nonconvulsive status epilepticus than the present study, most likely because it included adult patients in various stages of an altered mental status, some with observed overt seizures during their hospitalization. However, our results differ significantly from a recently published study by Towne et al. which found only 8% of comatose patients to be in nonconvulsive status epilepticus [5]. One potential reason for this discrepancy is the referral bias that may exist at our comprehensive epilepsy center in a tertiary care facility. Another possible explanation is the timing of the electroencephalographic study. Towne et al. recorded electroencephalograms within 3 days of coma onset. In the present study, the interval between the onset of unresponsiveness and the electroencephalography was more variable. We recognize the limitations of using electroencephalography alone as a tool for diagnosing the etiology of unresponsiveness and, furthermore, diagnosing these patients with nonconvulsive status epilepticus on this basis. The classification of nonconvulsive status epilepticus used in this study also included generalized synchronous discharges. Of the patients we found to be in nonconvulsive status epilepticus, approximately one half revealed generalized synchronous discharges. Recently Niedermeyer et al. commented on this electroencephalographic pattern in critically ill patients with “acute, complicating brain disease” [6]. They found this electroencephalographic abnormality to be often correlated with anoxic brain injury. The authors believe that under these circumstances, it is more likely that these generalized synchronous discharges are the result of an acute encephalopathic process rather than nonconvulsive status epilepticus. Considering that our electroencephalographic records were interpreted without knowledge of the patient’s primary diagnosis or medical history, it is possible that some of our patients would also fit into this category. However, it is also possible that these generalized synchronous discharges are secondarily generalized from initial partial seizures as also observed by Thomson et al. [7]. In the present study, generalized nonconvulsive status epilepticus occurred more frequently than partial nonconvulsive status epilepticus, which is in contrast to other reports [4,7]. However, these studies were not restricted to
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pediatric patients and this difference in findings may raise the issue of different etiologic processes of unresponsiveness in adults and children [6-8]. In contrast to previous studies in adults, in our pediatric patients a predominance of seizure origin in the left hemisphere was not observed, as is often reported in adults. Dean et al. reported a left-sided predominance in their analysis of epileptiform discharges on routine electroencephalography [9]. The evenly divided hemispheral dominance of seizure origin in the present study could reflect the early stage of brain development. The occurrence of periodic lateralized epileptiform discharges, which is considered to be an interictal pattern, is rare in pediatric patients. The characterization of periodic lateralized epileptiform discharges as an ictal electroencephalographic pattern is controversial. It has also been characterized as an ictal pattern [10]. Periodic lateralized epileptiform discharges were an uncommon occurrence in the unresponsive patients included in this study (2%). The inclusion of only one patient, who had an ictal pattern to his periodic lateralized epileptiform discharges, in our nonconvulsive status epilepticus group does not significantly affect the results of the present study. As previously reported by Towne et al. and others in adult patients with altered mental status, we also observed that the majority of unresponsive patients had moderate to severe diffuse cerebral disturbance of cortical activity [5]. It is also of interest to observe that in this study group, theta coma was nonexistent and alpha coma was rare, and a burst-suppression pattern also occurred much less commonly than electroencephalographic patterns consistent with nonconvulsive status epilepticus. Early identification of nonconvulsive status epilepticus can lead to improved patient outcome. In adults, nonconvulsive status epilepticus carries a poor prognosis, treatment is controversial, and outcome is generally poor. This observation may or may not be true for pediatric patients, as the etiology of nonconvulsive status epilepticus often differs in adults and children. However, a study of pediatric patents by O’Regan et al. suggests that continuous epileptiform discharges (without clinical seizures) may be harmful as evidenced by elevation of neuron specific enolase [11]. Conclusions The findings of this study suggest that nonconvulsive status epilepticus is not an uncommon pattern in unresponsive pediatric patients. This pattern was observed in one third of the patients in this study. Critically ill patients with unexplained altered mental status should be promptly considered for intermittent or continuous electroencephalographic monitoring to detect clinically inapparent seizures. We believe that more studies of this type are required to determine the etiologies and potential treatment of unconsciousness in the general pediatric population. In the
future, we plan to further study electroencephalographic patterns in unresponsive pediatric patients. But more importantly, we will attempt to correlate clinical and electroencephalographic responses to various treatment options in nonconvulsive status epilepticus. References [1] Alehan FK, Morton LD, Pellock JM. Utility of electroencephalography in the pediatric emergency department. J Child Neurol 2001; 16:484-7. [2] Hauser WA, Annegers JF, Kurland LT. The prevalence of epilepsy in Rochester, Minnesota, 1940-1980. Epilepsia 1991;32:429-45. [3] Kaplan PW. Assessing the outcomes in patients with nonconvulsive status epilepticus: Nonconvulsive status epilepticus is underdiagnosed, potentially overtreated, and confounded by comorbidity. J Clin Neurophysiol 1999;16:341-52. [4] Privitera M, Hoffman M, Moore JL. EEG detection of nontonic-
clonic status epilepticus in patients with altered consciousness. Epilepsy Res 1994;18:155-66. [5] Towne AR, Waterhouse EJ, Boggs JG. Prevalence of nonconvulsive status epilepticus in comatose patients. Neurology 2000;54: 340-5. [6] Niedermeyer E, Ribeiro M. Considerations of nonconvulsive status epilepticus. Clin Electroencephalogr 2000;31:192-5. [7] Thomson T, Svanborg E, Wedlund J. Nonconvulsive status epilepticus: High incidence of complex partial status. Epilepsia 1986;27: 276-85. [8] Garzon E, Fernandes RM, Sakamoto AC. Serial EEG during human status epilepticus: Evidence for PLED as an ictal pattern. Neurology 2001;57:1175-83. [9] Dean A, Solomon G, Labar D. Left hemispheric dominance of epileptiform discharges. Epilepsia 1997;38:503-5. [10] Brenner RP. Is it status? Epilepsia 2002;43(Suppl. 3):103-13. [11] O’Regan ME, Brown JK. Serum neuron specific enolase: A marker for neuronal dysfunction in children with continuous EEG epileptiform activity. Eur J Paediatr Neurol 1998;2:193-7.
Hosain et al: EEG in Unresponsive Children 165
Introduction Determining the etiology of a change in mental status in unresponsive patients can be challenging; electroencepha-
From the Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York.
162
PEDIATRIC NEUROLOGY
Vol. 32 No. 3
lography may be extremely helpful in such situations. In fact, this neurophysiologic modality is necessary to diagnose nonconvulsive status epilepticus, which is potentially a treatable condition. Electroencephalography is routinely performed on patients, who after experiencing overt seizures, have persistently altered mental status. In a recent electroencephalographic study of pediatric patients in the emergency department, Alehan et al. found that 5 of 21 patients presenting in the emergency department with altered mental status and acute confusional state were in nonconvulsive status epilepticus as determined by electroencephalography [1]. However, an electroencephalogram is not routinely requested for the evaluation of patients in unresponsive states of undetermined etiology without accompanying obvious clinical signs of seizures. In addition, the incidence of seizures is higher in the first decade of life compared with that for other age groups [2]. Therefore it is necessary to consider status epilepticus as one of the likely etiologies of an altered mental states in children with or without a prior history of seizures. There are two major types of status epilepticus, convulsive and nonconvulsive status epilepticus. Convulsive status epilepticus is an easily recognizable entity. Nonconvulsive status epilepticus is more heterogeneous and controversial in its definition. It is often defined as an epileptic state lasting more than 30 minutes, with seizure activity on electroencephalogram associated with an alteration in mental status [3]. However, nonconvulsive status epilepticus is not easy to recognize clinically, and patients in unresponsive states are frequently suspected of being in nonconvulsive status epilepticus. There are few reports on the electroencephalographic pattern in obtunded or unresponsive pediatric patients. Privitera et al. reported a 37% incidence of nonconvulsive status epilepticus in unresponsive adult patients [4]. However, the incidence of nonconvulsive status epilepticus in unresponsive pediatric patients is unknown. In addition, few large-scale studies of
Communications should be addressed to: Dr. Hosain; Department of Neurology and Neuroscience; Weil-Cornell Medical Center; 525 East 68th Street; Suite K-615; New York, NY 10021. Received February 2, 2004; accepted September 8, 2004.
© 2005 by Elsevier Inc. All rights reserved. doi:10.1016/j.pediatrneurol.2004.09.008 ● 0887-8994/05/$—see front matter
the utility of electroencephalography for the evaluation of patients in unresponsive states without overt signs of seizure activity have been published. We were interested in studying electroencephalographic patterns of unresponsive children and infants without overt seizures. Nonconvulsive status epilepticus can be subdivided into two groups: complex partial status epilepticus with lateralized epileptiform features and generalized nonconvulsive status epilepticus with bilateral synchronous discharges. In this study, the incidence and specific electroencephalographic patterns of nonconvulsive status epilepticus in pediatric patients over a 3-year period were evaluated. Methods All inpatient electroencephalographic studies performed in our hospital over a 3-year period (1999-2001) were retrospectively reviewed. We identified 178 pediatric patients for whom an electroencephalogram was requested owing to the patients’ persistent unresponsiveness. These patients were examined by a pediatric neurologist or intensivists and had neither overt clinical seizures nor pharmacologic agents that could result in an altered mental status. These electroencephalographic studies were requested by intensivists and neurologists for patients admitted to intensive care units. All of the electroencephalographic recordings were performed continuously for 30 minutes using the 10-20 system, following the standard recommendations of the American Electroencephalography Society. All electroencephalograms were interpreted by two independent board certified electroencephalographers. The electroencephalography interpreters were unaware of patients’ actual clinical diagnoses and past medical history. The electroencephalographic patterns in unresponsive patients were classified into two major categories: A. The first pattern was that of nonconvulsive status epilepticus, consisting of one or more of the following: (a) continuous or nearly continuous spike-and-wave discharges; (b) electrographic partial seizures; (c) periodic lateralized epileptiform discharges with runs of evolving epileptiform activity. B. The second category of electroencephalographic findings consisted of: (a) interictal spikes and sharp waves and periodic lateralized epileptiform discharges; (b) diffuse cerebral dysfunction; (c) alpha coma; (d) burst-suppression pattern; (e) triphasic waves.
Table 1.
EEG abnormalities in unresponsive children
EEG Abnormality
Number of Patients*
%
Left hemispheric NCSE Right hemispheric NCSE Generalized NCSE Left PLEDs Right PLEDs Bilateral PLEDs (or BiPEDs) Alpha coma Theta coma Burst suppression Interictal epileptiform activity Diffuse cerebral dysfunction (total) Diffuse cerebral dysfunction (not in NCSE) Triphasic waves
13 13 32 1 3 0 2 0 4 23 149 120 6
7.5 7.5 18 0.6 1.6 0 1 0 2 13 84 67 3
* Includes all patients in the study (n ⫽ 178). Abbreviations: BiPEDs ⫽ Bilateral independent periodic epileptiform discharges EEG ⫽ Electroencephalographic NCSE ⫽ Nonconvulsive status epilepticus PLEDs ⫽ Periodic lateralized epileptiform discharges
in partial nonconvulsive status epilepticus, there was no hemispheral predominance (right ⫽ 13 vs left ⫽ 13). The remaining 120 patients (67%) not in nonconvulsive status epilepticus manifested diffuse cerebral dysfunction, with the majority having severe diffuse cerebral dysfunction. Of the patients with diffuse cerebral dysfunction who were not in nonconvulsive status epilepticus, 22 (12%) manifested interictal epileptiform activity (spikes or sharp waves, or both). Four patients (2%) had periodic lateralized epileptiform discharges, one of whom had an ictal pattern. This individual was the only patient with periodic lateralized epileptiform discharges included in the nonconvulsive status epilepticus group. Two patients (1%) had an alpha coma pattern and four (2%) patients were in nonpharmacologic burst suppression. Only 6 patients (3%) had triphasic waves, suggesting a metabolic encephalopathy.
Results Discussion A total of 178 electroencephalographic studies on unresponsive pediatric patients were identified over a 3-year period. The mean age was 7.9 years (range, 1 day-18 years). Seventy-eight patients (44%) were female, and 100 (56%) were male. Seventy-two patients (40%) were less than 1 year old. The results of the study are summarized in Table 1. Fifty-eight patients (33%) manifested electroencephalographic patterns consistent with nonconvulsive status epilepticus. Thirty-six percent of the patients under the age of 1 year manifested electroencephalographic patterns consistent with nonconvulsive status epilepticus. Of the patients with nonconvulsive status epilepticus, 32 patients (18%) had generalized and 26 patients (15%) had partial nonconvulsive status epilepticus patterns. For the patients
Routine electroencephalograms are typically performed for more than one half hour in duration. Therefore this neurophysiologic study can have a high degree of sensitivity and specificity for identifying nonconvulsive status epilepticus. This study was conducted to identify the causes of unresponsiveness, as well as the incidence of nonconvulsive status epilepticus in pediatric patients. Because there are few comparative pediatric studies, we also compared our results to analogous adult data. Nonconvulsive status epilepticus electroencephalographic patterns were documented in one third of the unresponsive pediatric patients included in this study, which is a surprisingly high percentage. Of the patients less than 1 year of age, even a higher proportion (36%)
Hosain et al: EEG in Unresponsive Children 163
were in nonconvulsive status epilepticus. In a small cohort of patients (n ⫽ 15) Alehan et al. [1] reported a 29% incidence of nonconvulsive status epilepticus as diagnosed by electroencephalography for pediatric patients evaluated in the emergency room setting. The incidence of nonconvulsive status epilepticus in the present study is similar to that reported by Alehan et al. and that reported in an adult study by Privitera et al. [1,4]. In the adult study, Privitera et al. reported that 59 (37%) of 198 patients with altered consciousness (its degree varied from confusion interrupted by seizures to coma) were in a state of nonconvulsive status epilepticus, 23 without evident clinical manifestations and 36 exhibiting subtle motor activity. Their report revealed a slightly higher rate of nonconvulsive status epilepticus than the present study, most likely because it included adult patients in various stages of an altered mental status, some with observed overt seizures during their hospitalization. However, our results differ significantly from a recently published study by Towne et al. which found only 8% of comatose patients to be in nonconvulsive status epilepticus [5]. One potential reason for this discrepancy is the referral bias that may exist at our comprehensive epilepsy center in a tertiary care facility. Another possible explanation is the timing of the electroencephalographic study. Towne et al. recorded electroencephalograms within 3 days of coma onset. In the present study, the interval between the onset of unresponsiveness and the electroencephalography was more variable. We recognize the limitations of using electroencephalography alone as a tool for diagnosing the etiology of unresponsiveness and, furthermore, diagnosing these patients with nonconvulsive status epilepticus on this basis. The classification of nonconvulsive status epilepticus used in this study also included generalized synchronous discharges. Of the patients we found to be in nonconvulsive status epilepticus, approximately one half revealed generalized synchronous discharges. Recently Niedermeyer et al. commented on this electroencephalographic pattern in critically ill patients with “acute, complicating brain disease” [6]. They found this electroencephalographic abnormality to be often correlated with anoxic brain injury. The authors believe that under these circumstances, it is more likely that these generalized synchronous discharges are the result of an acute encephalopathic process rather than nonconvulsive status epilepticus. Considering that our electroencephalographic records were interpreted without knowledge of the patient’s primary diagnosis or medical history, it is possible that some of our patients would also fit into this category. However, it is also possible that these generalized synchronous discharges are secondarily generalized from initial partial seizures as also observed by Thomson et al. [7]. In the present study, generalized nonconvulsive status epilepticus occurred more frequently than partial nonconvulsive status epilepticus, which is in contrast to other reports [4,7]. However, these studies were not restricted to
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pediatric patients and this difference in findings may raise the issue of different etiologic processes of unresponsiveness in adults and children [6-8]. In contrast to previous studies in adults, in our pediatric patients a predominance of seizure origin in the left hemisphere was not observed, as is often reported in adults. Dean et al. reported a left-sided predominance in their analysis of epileptiform discharges on routine electroencephalography [9]. The evenly divided hemispheral dominance of seizure origin in the present study could reflect the early stage of brain development. The occurrence of periodic lateralized epileptiform discharges, which is considered to be an interictal pattern, is rare in pediatric patients. The characterization of periodic lateralized epileptiform discharges as an ictal electroencephalographic pattern is controversial. It has also been characterized as an ictal pattern [10]. Periodic lateralized epileptiform discharges were an uncommon occurrence in the unresponsive patients included in this study (2%). The inclusion of only one patient, who had an ictal pattern to his periodic lateralized epileptiform discharges, in our nonconvulsive status epilepticus group does not significantly affect the results of the present study. As previously reported by Towne et al. and others in adult patients with altered mental status, we also observed that the majority of unresponsive patients had moderate to severe diffuse cerebral disturbance of cortical activity [5]. It is also of interest to observe that in this study group, theta coma was nonexistent and alpha coma was rare, and a burst-suppression pattern also occurred much less commonly than electroencephalographic patterns consistent with nonconvulsive status epilepticus. Early identification of nonconvulsive status epilepticus can lead to improved patient outcome. In adults, nonconvulsive status epilepticus carries a poor prognosis, treatment is controversial, and outcome is generally poor. This observation may or may not be true for pediatric patients, as the etiology of nonconvulsive status epilepticus often differs in adults and children. However, a study of pediatric patents by O’Regan et al. suggests that continuous epileptiform discharges (without clinical seizures) may be harmful as evidenced by elevation of neuron specific enolase [11]. Conclusions The findings of this study suggest that nonconvulsive status epilepticus is not an uncommon pattern in unresponsive pediatric patients. This pattern was observed in one third of the patients in this study. Critically ill patients with unexplained altered mental status should be promptly considered for intermittent or continuous electroencephalographic monitoring to detect clinically inapparent seizures. We believe that more studies of this type are required to determine the etiologies and potential treatment of unconsciousness in the general pediatric population. In the
future, we plan to further study electroencephalographic patterns in unresponsive pediatric patients. But more importantly, we will attempt to correlate clinical and electroencephalographic responses to various treatment options in nonconvulsive status epilepticus. References [1] Alehan FK, Morton LD, Pellock JM. Utility of electroencephalography in the pediatric emergency department. J Child Neurol 2001; 16:484-7. [2] Hauser WA, Annegers JF, Kurland LT. The prevalence of epilepsy in Rochester, Minnesota, 1940-1980. Epilepsia 1991;32:429-45. [3] Kaplan PW. Assessing the outcomes in patients with nonconvulsive status epilepticus: Nonconvulsive status epilepticus is underdiagnosed, potentially overtreated, and confounded by comorbidity. J Clin Neurophysiol 1999;16:341-52. [4] Privitera M, Hoffman M, Moore JL. EEG detection of nontonic-
clonic status epilepticus in patients with altered consciousness. Epilepsy Res 1994;18:155-66. [5] Towne AR, Waterhouse EJ, Boggs JG. Prevalence of nonconvulsive status epilepticus in comatose patients. Neurology 2000;54: 340-5. [6] Niedermeyer E, Ribeiro M. Considerations of nonconvulsive status epilepticus. Clin Electroencephalogr 2000;31:192-5. [7] Thomson T, Svanborg E, Wedlund J. Nonconvulsive status epilepticus: High incidence of complex partial status. Epilepsia 1986;27: 276-85. [8] Garzon E, Fernandes RM, Sakamoto AC. Serial EEG during human status epilepticus: Evidence for PLED as an ictal pattern. Neurology 2001;57:1175-83. [9] Dean A, Solomon G, Labar D. Left hemispheric dominance of epileptiform discharges. Epilepsia 1997;38:503-5. [10] Brenner RP. Is it status? Epilepsia 2002;43(Suppl. 3):103-13. [11] O’Regan ME, Brown JK. Serum neuron specific enolase: A marker for neuronal dysfunction in children with continuous EEG epileptiform activity. Eur J Paediatr Neurol 1998;2:193-7.
Hosain et al: EEG in Unresponsive Children 165