Acta Neurol Scand 2015: 132: 423–429 DOI: 10.1111/ane.12412
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd ACTA NEUROLOGICA SCANDINAVICA
Higher ratio of ischemic stroke to hemorrhagic stroke in summer Shigematsu K, Watanabe Y, Nakano H. On behalf of the Kyoto Stroke Registry Committee. Higher ratio of ischemic stroke to hemorrhagic stroke in summer. Acta Neurol Scand 2015: 132: 423–429. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Background – The aim of this study was to investigate the seasonal variation of the ratio of hemorrhagic stroke to ischemic stroke. The working hypothesis is that the ratio may vary among seasons. Methods – A total of 13,788 patients registered in the Kyoto Stroke Registry from 1999 to 2009 were divided into 4 groups based on the season in which stroke developed. We calculated odds ratio (OR) for the incidence of stroke as a whole, cerebral infarction (CeI), cerebral hemorrhage (CH), and subarachnoid hemorrhage (SAH) in spring, autumn, and winter setting summer as a reference. Using a logistic regression, we evaluated the seasonal variation of ORs for CH/CeI and for SAH/CeI with adjustment for age, gender, and risk factors. Results – Incidence of CeI in autumn was lower than in summer (OR: 0.93; 0.87–0.98, P = 0.013). Incidence of CH was higher in spring (OR: 1.36; 1.23–1.49, P < 0.001), in autumn (OR: 1.16; 1.05–1.28, P = 0.004), and in winter (OR: 1.37; 1.25–1.51, P < 0.001) than in summer. Incidence of SAH was higher in spring (OR: 1.51; 1.28–1.79, P < 0.001) and in winter (OR: 1.44; 1.22–1.70, P < 0.001) than in summer. OR for CH/CeI in spring, autumn, and winter were 1.28 (1.13–1.45, P < 0.001), 1.26 (1.11–1.43, P < 0.001), and 1.35 (1.19–1.53, P < 0.001), respectively. ORs for SAH/CeI were 1.46 (1.19–1.79, P < 0.001), 1.34 (1.09–1.66, P = 0.007), and 1.50 (1.22–1.84, P < 0.001), respectively. Conclusions – Seasonal variations differed among stroke subtypes. The OR for CH/CeI and for SAH/ CeI was lower in summer and higher in the rest of seasons independent of age, gender, and risk factors.
Introduction
The aim of this study was to investigate the seasonal variation in the ratio of hemorrhagic stroke (HS) to ischemic stroke (IS). The working hypothesis of the study is that the ratio would be low in summer and high in winter. Seasonal variation in stroke incidence has been repeatedly reported (1–6), and similar variation has also been reported in myocardial infarction (7–10). However, data on the comparison of the variations among three major stroke subtypes, that is, cerebral infarction (CeI), cerebral hemorrhage (CH), and subarachnoid hemorrhage (SAH), are sparse. It remains unclear whether there is a difference in seasonal variation among
K. Shigematsu1, Y. Watanabe2, H. Nakano3, On behalf of the Kyoto Stroke Registry Committee 1 Department of Neurology, National Hospital Organization, Minami Kyoto Hospital, Kyoto, Japan; 2 Department of Epidemiology for Community Health and Medicine, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, Kyoto, Japan; 3Department of Neurosurgery, Kyoto Kidugawa Hospital, Joyo, Kyoto, Japan
Key words: seasonal variation; ischemic stroke; hemorrhagic stroke K. Shigematsu, Department of Neurology, National Hospital Organization, Minami Kyoto Hospital, 11 Nakaashihara, Joyo, Kyoto 610-0113, Japan Tel.: 81-774-52-0065 Fax: 81-75-821-9610 e-mail: [email protected] Accepted for publication March 25, 2015
the subtypes and how different it is, if there is a difference. Stroke can be divided into two major groups: IS and HS. The former represents CeI, in which cerebral blood flow is interrupted by vascular obstruction. The latter represents CH and SAH, in which blood flow is interrupted by vascular rupture. All are cerebrovascular lesions equally associated with impairment of the cerebral circulation, but they differ widely in terms of pathology. We hypothesized two factors as major causes of seasonal variation in stroke; hemoconcentration possibly due to dehydration in summer and elevated blood pressure in winter. The former would disturb cerebral blood flow and trigger IS and the latter would damage cerebral wall and trigger HS. If this is the case, HS/IS would 423
Shigematsu et al. be low in summer and high in winter. It is worthwhile to test the hypothesis because both dehydration and seasonal elevation of blood pressure are preventable. Methods
We analyzed all stroke patients identified from January 1999 to December 2009 inclusive in the entire Kyoto prefecture and registered in the KSR. The details of the KSR have been previously reported (11–16). Briefly, stroke patients were registered in the KSR in cooperation with all medical institutions belonging to the Kyoto Medical Association (KMA). The KMA distributes the registration form to all cooperative facilities, and physicians in charge at cooperative facilities fill the form and send it back to the Medical Association. A total of 151 hospitals registered patients. The registration items include age, gender, date of onset, past medical history (hypertension, arrhythmia, diabetes mellitus, and hyperlipidemia), blood pressure on consultation and history of examinations (CT, MRI). Stroke was classified into 3 major subtypes; CeI, CH, and SAH according to the WHO definition (17). All stroke patients were divided into 4 groups based on the season (winter; December–February, spring; March–May, summer; June–August and autumn; September–November) in which stroke developed. The numbers of days in winter, spring, summer, and autumn over the 11-year survey period (4007 days) were 993, 1012, 1001, and 1001 days, respectively, and the incidence of stoke by season was adjusted with these numbers of days: the number of cases/993 9 4007/4, the number of cases/ 1012 9 4007/4, the number of cases/1001 9 4007/ 4, and the number of cases/1001 9 4007/4, respectively. Firstly, the significance of differences in the incidence among the seasons was analyzed using the chi-square test. For numerical data such as age and blood pressure, a Student t-test was used. Then, using a multinomial logistic analysis, OR of stroke developed in spring, in autumn and in winter compared to stroke developed in summer was calculated. We set summer as a reference because the adjusted prevalence of stroke was the lowest in summer. Similarly, we estimated OR of stroke as a whole as well as CeI, CH, and SAH in each season. From such models, 3 regression coefficients were estimated, which provide estimates of OR of stroke occurring in spring, autumn and winter versus summer as a reference. 424
OR was calculated as eb with 95%CI = e(b 1.96 9 SE). Here, ‘b’ is the regression coefficient corresponding to spring, autumn, or winter (setting summer as a reference), and ‘SE’ is the standard error of ‘b’. A multinomial logistic analysis with adjustment for this age, gender, and medical history was performed referring to the prevalence in summer as a reference. Finally, ORs of incidence of CH and SAH compared to CeI in each season setting summer as a reference (e.g., OR of CH/CeI in spring compared to CH/CeI in summer, OR of CH/CeI in autumn compared to CH/CeI in summer, and so on) were calculated using a binominal logistic analysis adjusted for age, gender, and risk factors (history of hypertension, arrhythmia, diabetes mellitus, and hyperlipidemia). All reported P-values were two sided. A P-value of
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd ACTA NEUROLOGICA SCANDINAVICA
Higher ratio of ischemic stroke to hemorrhagic stroke in summer Shigematsu K, Watanabe Y, Nakano H. On behalf of the Kyoto Stroke Registry Committee. Higher ratio of ischemic stroke to hemorrhagic stroke in summer. Acta Neurol Scand 2015: 132: 423–429. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd. Background – The aim of this study was to investigate the seasonal variation of the ratio of hemorrhagic stroke to ischemic stroke. The working hypothesis is that the ratio may vary among seasons. Methods – A total of 13,788 patients registered in the Kyoto Stroke Registry from 1999 to 2009 were divided into 4 groups based on the season in which stroke developed. We calculated odds ratio (OR) for the incidence of stroke as a whole, cerebral infarction (CeI), cerebral hemorrhage (CH), and subarachnoid hemorrhage (SAH) in spring, autumn, and winter setting summer as a reference. Using a logistic regression, we evaluated the seasonal variation of ORs for CH/CeI and for SAH/CeI with adjustment for age, gender, and risk factors. Results – Incidence of CeI in autumn was lower than in summer (OR: 0.93; 0.87–0.98, P = 0.013). Incidence of CH was higher in spring (OR: 1.36; 1.23–1.49, P < 0.001), in autumn (OR: 1.16; 1.05–1.28, P = 0.004), and in winter (OR: 1.37; 1.25–1.51, P < 0.001) than in summer. Incidence of SAH was higher in spring (OR: 1.51; 1.28–1.79, P < 0.001) and in winter (OR: 1.44; 1.22–1.70, P < 0.001) than in summer. OR for CH/CeI in spring, autumn, and winter were 1.28 (1.13–1.45, P < 0.001), 1.26 (1.11–1.43, P < 0.001), and 1.35 (1.19–1.53, P < 0.001), respectively. ORs for SAH/CeI were 1.46 (1.19–1.79, P < 0.001), 1.34 (1.09–1.66, P = 0.007), and 1.50 (1.22–1.84, P < 0.001), respectively. Conclusions – Seasonal variations differed among stroke subtypes. The OR for CH/CeI and for SAH/ CeI was lower in summer and higher in the rest of seasons independent of age, gender, and risk factors.
Introduction
The aim of this study was to investigate the seasonal variation in the ratio of hemorrhagic stroke (HS) to ischemic stroke (IS). The working hypothesis of the study is that the ratio would be low in summer and high in winter. Seasonal variation in stroke incidence has been repeatedly reported (1–6), and similar variation has also been reported in myocardial infarction (7–10). However, data on the comparison of the variations among three major stroke subtypes, that is, cerebral infarction (CeI), cerebral hemorrhage (CH), and subarachnoid hemorrhage (SAH), are sparse. It remains unclear whether there is a difference in seasonal variation among
K. Shigematsu1, Y. Watanabe2, H. Nakano3, On behalf of the Kyoto Stroke Registry Committee 1 Department of Neurology, National Hospital Organization, Minami Kyoto Hospital, Kyoto, Japan; 2 Department of Epidemiology for Community Health and Medicine, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, Kyoto, Japan; 3Department of Neurosurgery, Kyoto Kidugawa Hospital, Joyo, Kyoto, Japan
Key words: seasonal variation; ischemic stroke; hemorrhagic stroke K. Shigematsu, Department of Neurology, National Hospital Organization, Minami Kyoto Hospital, 11 Nakaashihara, Joyo, Kyoto 610-0113, Japan Tel.: 81-774-52-0065 Fax: 81-75-821-9610 e-mail: [email protected] Accepted for publication March 25, 2015
the subtypes and how different it is, if there is a difference. Stroke can be divided into two major groups: IS and HS. The former represents CeI, in which cerebral blood flow is interrupted by vascular obstruction. The latter represents CH and SAH, in which blood flow is interrupted by vascular rupture. All are cerebrovascular lesions equally associated with impairment of the cerebral circulation, but they differ widely in terms of pathology. We hypothesized two factors as major causes of seasonal variation in stroke; hemoconcentration possibly due to dehydration in summer and elevated blood pressure in winter. The former would disturb cerebral blood flow and trigger IS and the latter would damage cerebral wall and trigger HS. If this is the case, HS/IS would 423
Shigematsu et al. be low in summer and high in winter. It is worthwhile to test the hypothesis because both dehydration and seasonal elevation of blood pressure are preventable. Methods
We analyzed all stroke patients identified from January 1999 to December 2009 inclusive in the entire Kyoto prefecture and registered in the KSR. The details of the KSR have been previously reported (11–16). Briefly, stroke patients were registered in the KSR in cooperation with all medical institutions belonging to the Kyoto Medical Association (KMA). The KMA distributes the registration form to all cooperative facilities, and physicians in charge at cooperative facilities fill the form and send it back to the Medical Association. A total of 151 hospitals registered patients. The registration items include age, gender, date of onset, past medical history (hypertension, arrhythmia, diabetes mellitus, and hyperlipidemia), blood pressure on consultation and history of examinations (CT, MRI). Stroke was classified into 3 major subtypes; CeI, CH, and SAH according to the WHO definition (17). All stroke patients were divided into 4 groups based on the season (winter; December–February, spring; March–May, summer; June–August and autumn; September–November) in which stroke developed. The numbers of days in winter, spring, summer, and autumn over the 11-year survey period (4007 days) were 993, 1012, 1001, and 1001 days, respectively, and the incidence of stoke by season was adjusted with these numbers of days: the number of cases/993 9 4007/4, the number of cases/ 1012 9 4007/4, the number of cases/1001 9 4007/ 4, and the number of cases/1001 9 4007/4, respectively. Firstly, the significance of differences in the incidence among the seasons was analyzed using the chi-square test. For numerical data such as age and blood pressure, a Student t-test was used. Then, using a multinomial logistic analysis, OR of stroke developed in spring, in autumn and in winter compared to stroke developed in summer was calculated. We set summer as a reference because the adjusted prevalence of stroke was the lowest in summer. Similarly, we estimated OR of stroke as a whole as well as CeI, CH, and SAH in each season. From such models, 3 regression coefficients were estimated, which provide estimates of OR of stroke occurring in spring, autumn and winter versus summer as a reference. 424
OR was calculated as eb with 95%CI = e(b 1.96 9 SE). Here, ‘b’ is the regression coefficient corresponding to spring, autumn, or winter (setting summer as a reference), and ‘SE’ is the standard error of ‘b’. A multinomial logistic analysis with adjustment for this age, gender, and medical history was performed referring to the prevalence in summer as a reference. Finally, ORs of incidence of CH and SAH compared to CeI in each season setting summer as a reference (e.g., OR of CH/CeI in spring compared to CH/CeI in summer, OR of CH/CeI in autumn compared to CH/CeI in summer, and so on) were calculated using a binominal logistic analysis adjusted for age, gender, and risk factors (history of hypertension, arrhythmia, diabetes mellitus, and hyperlipidemia). All reported P-values were two sided. A P-value of
