Five Years after the "Pocket Monster" Seizures
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《新英格兰医药杂志》
To the Editor: In December 1997, many children, and even some adults, in Japan who were watching the television cartoon program "Pocket Monster," or "Pokemon," had epileptic seizures.1,2 Because the program was very popular, this incident had a strong impact on the people in Japan and also attracted worldwide attention. We conducted a five-year follow-up study to determine the rate of recurrence of seizures and the factors associated with recurrence.
We sent questionnaires to the physicians who treated 103 patients with "Pocket Monster" seizures. Data for 91 patients were available. A photoparoxysmal response was defined as generalized spike-wave complexes induced by intermittent photic stimulation. The patients were divided into two groups: the epilepsy group included 24 patients with a history of epilepsy, and the no-epilepsy group included 67 patients with no history of the disorder.
Of the 91 patients, 25 (27 percent) had a recurrence of seizures: 13 (19 percent) of the 67 patients in the no-epilepsy group and 12 (50 percent) of the 24 in the epilepsy group (P=0.007).
In the no-epilepsy group, unadjusted analysis revealed that a history of febrile convulsion before the age of 12 years was correlated with a recurrence of seizures (Table 1). The proportion of patients with a photoparoxysmal response was the same among the patients with a recurrence and those without a recurrence. Multiple regression analysis showed that only an age of less than 12 years was associated with a recurrence (odds ratio, 13.2; 95 percent confidence interval, 1.18 to 143; P=0.037). Among the 13 patients who had a recurrence, juvenile myoclonic epilepsy was the most common diagnosis (in 6 patients), followed by nonspecific idiopathic generalized epilepsy (4 patients). The median interval between the "Pocket Monster" incident and a recurrence was 37 months (range, 0 to 58).
Table 1. Characteristics of the Patients and Seizure Recurrences According to the Absence or Presence of a History of Epilepsy.
In the epilepsy group, unadjusted analysis showed that the absence of a photoparoxysmal response at the time of the incident and a history of seizures within the year before the incident were correlated with a recurrence of seizures (Table 1). Of 12 patients with a recurrence, 10 were found to have various localization-related epilepsies. The median interval between the incident and a recurrence was 6 months (range, 0 to 40).
Our study showed that the rate of recurrence of seizures among patients who had "Pocket Monster" seizures was associated with the presence or absence of a history of epilepsy. In the no-epilepsy group, most recurrences were in patients with an underlying idiopathic generalized epilepsy, such as juvenile myoclonic epilepsy and nonspecific idiopathic generalized epilepsy, in whom seizures would have been likely to develop eventually, even if the "Pocket Monster" seizures had not occurred. In the epilepsy group, a finding of intrinsic epileptogenicity rather than photosensitivity was closely related to a recurrence of seizures.
Akihisa Okumura, M.D.
Kazuyoshi Watanabe, M.D.
Nagoya University Graduate School of Medicine
Nagoya, Aichi 466-8550, Japan
Tatsuya Ishikawa, M.D.
Nagoya City University Graduate School of Medical Sciences
Nagoya, Aichi 467-8601, Japan
References
Takada H, Aso K, Watanabe K, Okumura A, Negoro T, Ishikawa T. Epileptic seizures induced by animated cartoon, "Pocket Monster." Epilepsia 1999;40:997-1002.
Ishida S, Yamashita Y, Matsuishi T, et al. Photosensitive seizures provoked while viewing "Pocket Monsters," a made-for-television animated cartoon program in Japan. Epilepsia 1998;39:1340-1344.
We sent questionnaires to the physicians who treated 103 patients with "Pocket Monster" seizures. Data for 91 patients were available. A photoparoxysmal response was defined as generalized spike-wave complexes induced by intermittent photic stimulation. The patients were divided into two groups: the epilepsy group included 24 patients with a history of epilepsy, and the no-epilepsy group included 67 patients with no history of the disorder.
Of the 91 patients, 25 (27 percent) had a recurrence of seizures: 13 (19 percent) of the 67 patients in the no-epilepsy group and 12 (50 percent) of the 24 in the epilepsy group (P=0.007).
In the no-epilepsy group, unadjusted analysis revealed that a history of febrile convulsion before the age of 12 years was correlated with a recurrence of seizures (Table 1). The proportion of patients with a photoparoxysmal response was the same among the patients with a recurrence and those without a recurrence. Multiple regression analysis showed that only an age of less than 12 years was associated with a recurrence (odds ratio, 13.2; 95 percent confidence interval, 1.18 to 143; P=0.037). Among the 13 patients who had a recurrence, juvenile myoclonic epilepsy was the most common diagnosis (in 6 patients), followed by nonspecific idiopathic generalized epilepsy (4 patients). The median interval between the "Pocket Monster" incident and a recurrence was 37 months (range, 0 to 58).
Table 1. Characteristics of the Patients and Seizure Recurrences According to the Absence or Presence of a History of Epilepsy.
In the epilepsy group, unadjusted analysis showed that the absence of a photoparoxysmal response at the time of the incident and a history of seizures within the year before the incident were correlated with a recurrence of seizures (Table 1). Of 12 patients with a recurrence, 10 were found to have various localization-related epilepsies. The median interval between the incident and a recurrence was 6 months (range, 0 to 40).
Our study showed that the rate of recurrence of seizures among patients who had "Pocket Monster" seizures was associated with the presence or absence of a history of epilepsy. In the no-epilepsy group, most recurrences were in patients with an underlying idiopathic generalized epilepsy, such as juvenile myoclonic epilepsy and nonspecific idiopathic generalized epilepsy, in whom seizures would have been likely to develop eventually, even if the "Pocket Monster" seizures had not occurred. In the epilepsy group, a finding of intrinsic epileptogenicity rather than photosensitivity was closely related to a recurrence of seizures.
Akihisa Okumura, M.D.
Kazuyoshi Watanabe, M.D.
Nagoya University Graduate School of Medicine
Nagoya, Aichi 466-8550, Japan
Tatsuya Ishikawa, M.D.
Nagoya City University Graduate School of Medical Sciences
Nagoya, Aichi 467-8601, Japan
References
Takada H, Aso K, Watanabe K, Okumura A, Negoro T, Ishikawa T. Epileptic seizures induced by animated cartoon, "Pocket Monster." Epilepsia 1999;40:997-1002.
Ishida S, Yamashita Y, Matsuishi T, et al. Photosensitive seizures provoked while viewing "Pocket Monsters," a made-for-television animated cartoon program in Japan. Epilepsia 1998;39:1340-1344.