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Byline: Ziauddin, Naveed Iqbal, Ishfaq Ahmad Shah, Zafar Ali, Haleem ur Rehman and Khalid Mehmood


Objective: To determine seasonal variation in the occurrence of stroke and its subtypes (ischemic stroke and hemorrhagic stroke) during summer and winter and to observe the frequency of common risk factors for stroke.

Methodology: The present descriptive study was conducted in the Department of Medicine, MTI Lady Reading Hospital Peshawar, Khyber Pakhtunkhwa, Pakistan, over a period of one year from 1st January 2014 to 31st December 2014. A total of 321 patients of any age and either gender were included. The diagnosis was established based on history, clinical examination and supplemented by CT scan of brain.

Results: In winter 58.56% of patients and in summer 41.48% of patients were presented. Ischemic stroke was present in 66.04% patients while hemorrhagic stroke in 33.95% patients. Males had more strokes as compared to females (60.75% Vs. 39.25%). In males highest number of strokes was found in 6069 age groups whereas in females it was in 50-59 age groups. In winter the strokes increased in all age groups comparative to summer. Hypertension (34.26%) was the highest risk factor for stroke.

Conclusion: Stroke showed seasonal variation. Winter season was associated with increased frequency of stroke and its subtype of hemorrhagic stroke. There was variation of gender, season and stroke types in different age groups. Hypertension was found to be the highest risk factor.

Key words: Stroke, Ischemic Stroke, hemorrhagic Stroke, Stroke risk factors, Seasonal variation.


Stroke is a major cause of social disability and death. It accounts for about 5.7 million deaths globally; 87% of which occur in developing countries1. Ischemic strokes comprise 85% while hemorrhagic strokes (intra-cerebral and sub-arachnoid) comprise 15%2.

Ischemic stroke is characterized by the sudden loss of blood circulation to an area of the brain, resulting in a corresponding loss of neurologic functions. Intra-cerebral hemorrhage (ICH) occurs when an already damaged or diseased blood vessel in the brain bursts that leaks blood inside the brain. This leakage of blood causes increase in the pressure upon the brain tissues and cells surrounding the blood. Increased pressure and blood accumulations may cause unconsciousness and ultimately death3.

Basal ganglia are considered the most frequent sites of bleed (55%) followed by thalamus (26%), cerebral hemispheres (11%), brain stem (8%) and cerebellum (7%)4.

Hypertension is found to be the most important risk factor for stroke (ICH and ischemic strokes). Other risk factors of ICH include trauma, infections, tumors, blood clotting deficiencies and abnormalities in blood vessels such as arterio-venous malformations5.

Stroke is also related to many other factors including smoking, gender, high intake of alcohols and seasonal variation6,7. Current smokers have increased risk as compared to ex-smokers. Men and women both are reported to have similar proneness toward ICH and ischemic strokes due to smoking8.

Similarly age is also a common factor that has increased impact on the occurrence of ICH in both males and females. Elderly persons have more tendencies to sustain ICH stroke presumably due to high blood pressure9.

Seasonal variations are common in ICH and ischemic strokes occurrence. A number of studies were carried out in several countries and different climatic regions10-17. However, the results varied according to study design, geography and climate leading to some discrepancy in results18-20.

Pakistan, being a tropical country, has different seasons. Exposure to extremes of temperature during summer and winter can influence stroke causation in a large population. The present study was aimed to determine if there is any evidence of seasonal variation in the occurrence of stroke and its subtypes, along with causal factors of stroke, the effect of age and gender on the occurrence of ICH and ischemic strokes in a teaching hospital of Khyber Pakhtunkhwa Pakistan. This may help clinical decision making in stroke prevention21.


The present study was conducted in the Department of Medicine at Medical Teaching Institute (MTI) Lady Reading Hospital, (LRH) Peshawar, Khyber Pakhtunkhwa, Pakistan. Data were obtained from the admission book of Medical units of LRH. The annual records were examined and analyzed for the estimation of ICH and ischemic stroke occurrence.

Total number of patients with stroke (hemorrhagic and ischemic) confirmed through CT scan, was 321. Khyber Pakhtunkhwa province has diverse weather conditions, but due to climate changes, two season i.e. spring and autumn are not specific to the environment that used to be in the past. So accordingly the year was sub divided in two season, the summer (April, May, June, July, August and September) and Winter (October, November, December, January, February and March). The seasonal stroke variation in one year time period was studied, from 1st January 2014 to 31st December 2014.

All patients who had ICH and ischemic stroke of either gender and any age were included in the study. We excluded sub-arachnoid hemorrhage, arterio-venous malformation, and venous stroke. Age, gender, type of stroke, date of admission and stroke onset were recorded of all patients.

After formal consent, patients fulfilling the inclusion criteria were further assessed through a detailed history of hypertension, diabetes mellitus, previous stroke, atrial fibrillation, smoking, coronary artery disease and dyslipidemia. Relevant investigations were carried out. The diagnosis of stroke was established based on history, clinical examination and supplemented by CT scan of brain.

Seasons were categorized into summer and winter. The data were recorded in the proforma and statistically analyzed through MS Excel 2013.


A total of 321 patients with stroke were included in the study.

Table 1 showed that there was variation of gender, season and stroke types in different age groups. Males had more strokes (195) as compared to females (126). In males highest numbers of strokes were found in 60-69 age groups whereas in females they were in 50-59 age groups. In winter the strokes increased in all age groups (less than 40, 6; 40-49, 22; 50-59, 47; 60-69,52; 70-79, 43; greater than 80, 18) compared to summer (less than 40,7; 40-49, 15; 50-59, 26; 60-69, 36; 70-79, 30; greater than 80, 19). Ischemic strokes patients were less than hemorrhagic stroke in 60-69 age group, while in all other age groups it was found high.

It was observed that the highest number of hemorrhage and ischemic strokes occurred in December and February, and least strokes were noticed in April. Highest hemorrhage stroke occurred in December (28), followed by August and November (10), respectively. The least hemorrhage stokes were observed in April (4). Ischemic strokes in patients were highest in January whereas least was observed in April (6).

In table 2 it was observed that the data of patients, ischemic and hemorrhage stroke related to seasonal variation was significant. The patients admitted in summer and winter had person chi-square value of 9.4 and is significant at 95 percent level. Similarly, the chi-square value of ischemic and hemorrhage stroke were 5.4 and 4.04, and were found significance at 95 percent level.

Various risk factors and their relative frequency for hemorrhagic/ ischemic stroke are shown in Figure 1.

Figure 2 showed that patients with hemorrhagic or ischemic stroke due to hypertension were 110, due to combination of hypertension and diabetes mellitus were 61 and due to combination of other risk factors (AF, smoking, dyslipidemia, CAD) were 8. Patients had high number of ischemic strokes in all 3 types of risk factors i.e. HTI (64), HDI (46), and MXI (6) compared to hemorrhage (46, 15 and 2).


Seasonal variation of stroke is a debatable issue. Several researchers looked into the possible association between the occurrence of stroke and various seasons of the year. A number of these studies carried out in various countries of the world showed an association12,16,18,19,22-25.

Statistically significant seasonal variation was observed regarding incidence of all strokes (p less than 0.01)18 and sub-types of strokes like hemorrhagic stroke (p less than 0.05)18 and ischemic stroke (p less than 0.01)12,18. Such variation in seasonality was not reported regarding sub-arachnoid hemorrhage18,26.

Besides variation in seasonality, a number of meteorological factors were also studied by various researchers. These included changes in ambient temperature, diurnal temperature changes and difference in atmospheric pressures. These were found to be associated with the occurrence of stroke17,27,28.

Table 1: Gender, season and stroke type with respect to age distribution (n=321)

###Age groups

###less than 40###40-49###50-59###60-69###70-79###greater than 80







Table 2: Distribution of patients, hemorrhage and ischemic stroke related to seasonal variation

###Summer###Winter###Total###Chi square###P-value


Ischemic Stroke###89###123###212###5.4###0.01


On the contrary, other investigators did not find evidence regarding seasonal variation in stroke20,29 or stroke subtype (i.e. ischemic stroke)15. These disagreements to the above mentioned studies may be due to differences in the study design, methodology, statistics and regional differences. Moreover, the sample size diversity and lack of statistical power for consistent results may also be considered responsible18-20.

The present study demonstrated that winter season had the highest number (58.56%) of patients with strokes. Hemorrhagic stroke occurred more frequently in winter than in summer. These findings were in line with Fang CW et al17, who showed that spontaneous ICH significantly occurred more in winter in Taiwan(p=0.002). Changes in temperature and lower ambient temperature were shown to be the likely reasons for more cases of ICH in Taiwan17.

Capon et al15, found increased frequency of stroke (23%) in November-December and decreased (10%) in July-August. These seasonal differences in frequency of stroke were statistically significant (pless than 0.05). Hemorrhagic stroke was also reported to be associated with ambient humidity and the decreased number of hours of sunshine.

Miah et al13, showed that hemorrhagic stroke was more frequent during winter (62.2%) than in summer (37.6%). Other studies observed similar findings6,15,18,30.

Winter and chilly weathers are reported to have more cases of ICH as compare to the warmer and hot climatic conditions. Several studies hypothesize an increase in blood pressure in winters than summers. These fluctuations in BP are considered to be important factor for increased frequency of ICH in winters30,31.

Similarly, in the waking hours of morning, there is increased in frequency of ICH19. The likely explanation for this may be that on awakening there is an increase in the sympathetic tone with resultant increase in blood pressure31.

Although the exact causes for increased frequency of strokes during the winter are not known, but several mechanisms may be suggested10.

First, the seasonal variation of blood pressure is well known, with blood pressure being higher in winter6,18,19. There is an increase in platelet count, blood viscosity and arterial pressure on exposure to low temperature. Due to cold-induced constriction of peripheral blood vessel, blood pressure is higher in colder months even within the same person. Raised blood pressure during the winter may be a possible trigger for ICH and IS27,31,32.

Second, total cholesterol and triglycerides tend to be higher in winter than in summer33. A significant seasonal pattern for the occurrence of hemorrhagic stroke was noted among persons with a high serum cholesterol level (p less than 0.05)18.

Moreover, there are significant seasonal variations in plasma fibrinogen concentration and viscosity. Fibrinogen is considered a significant predictor of stroke34,35.

Risk factors for stroke are also influenced by age and gender. In our study hemorrhagic and ischemic strokes were high in patients of 60-69 years of age (88 out of 321). These results were supported by Wang et al36, who examined 5 year case study in Australia. Frequency of stroke was found to be higher in greater than 65years of age.

Previous literature has reported that seasonal differences in stroke are greater in older than in younger age groups. Klimaszewska et al37, noted increased incidence of ischemic stroke in older patients during winter months than in summer months. In another study older females were found to be more prone to spontaneous ICH as a result of lower ambient temperature38. About17% of strokes are reported in elderly population. Stroke related mortality, morbidity and hospital stay in is increased in elderly population5,9,39,40.

Blood pressure is shown to be the most powerful risk factor for stroke. It has seasonal and diurnal variations which are responsible for variations in stroke onset32. In the current study, the major risk factor for stroke was hypertension (34.26%). In a meta-analysis by Boutayeb et al, it was shown that the frequency of hypertension in stroke patients is about 50 to 82% from different studies of Pakistan. Similarly was found to be greater than 25% in 36 studies, smoking greater than 15% in 26 studies and dyslipidemia greater than 25% in19 studies41. Mouradian et al showed that frequency of hypertension was 66% while dyslipidemia and diabetes were around 25%42.


There was seasonal variation noted in the occurrence of Strokes. Winter season was associated with increased frequency of stroke and its subtype of hemorrhagic stroke. There was variation of gender, season and stroke types in different age groups. Hypertension was found to be the highest risk factor.


1. Feigin VL, Forouzanfar MH, Krishnamurthi R, Mensah GA, Connor M, Bennett DA, et al. Global Burden of Diseases, Injuries, and Risk Factors Study 2010 (GBD 2010) and the GBD Stroke Experts Group. Global and regional burden of stroke during 1990-2010: findings from the Global Burden of Disease Study 2010. Lancet 2014; 383:245-54.

2. Shiber JR, Fontane E, Adewale A. Stroke registry: hemorrhagic vs ischemic strokes. Am J Emerg Med 2010; 28:331-3.

3. Qureshi MA, Jamshaid TD, Siddiqui AM. Stroke: a study of clinical patterns and risk factors. Ann King Edward Med Coll 2003; 9:98-100.

4. Zafar A, Khan FS. Clinical and radiological features of intracerebral haemorrhage in hypertensive patients. J Pak Med Assoc 2008; 58:356-8.

5. Afridi MAR, Ali Z, Muhammad R, Ahmad A, Alam I. Age and gender specific stroke risk factors in a teaching hospital in khyber pakhtunkhwa. J Postgrad Med Inst 2015; 29:76-82.

6. Jakovljevic D, Salomaa V, Sivenius J, Tamminen M, Sarti C, Salmi K, et al. Seasonal variation in the occurrence of stroke in a Finnish adult population. The FINMONICA Stroke Register. Finnish Monitoring Trends and Determinants in Cardiovascular Disease. Stroke 1996; 27:1774-9.

7. Ariesen MJ, Claus SP, Rinkel GJ, Algra A. Risk factors for intracerebral hemorrhage in the general population: a systematic review. Stroke 2003; 34:2060-5.

8. Shah RS, Cole JW. Smoking and stroke: the more you smoke the more you stroke. Expert Rev Cardiovasc Ther 2010; 8:917-32.

9. Russo T, Felzani G, Marini C. Stroke in the very old: a systematic review of studies on incidence, outcome, and resource use. J Aging Res 2011; 2011:108785.

10. Raj K, Bhatia R, Prasad K, Srivastava MV, Vishnebhatla S, Singh MB. Seasonal differences and circadian variation in stroke occurrence and stroke subtypes. J Stroke Cerebrovasc Dis 2015; 24:10-16.

11. Giua A, Abbas MA, Murgia N, Corea F. Climate and stroke: a controversial association. Int J Biometeorol 2010; 54:1-3.

12. Ogata T, Kimura K, Minematsu K, Kazui S, Yamaguchi T. Japan Multicenter Stroke Investigators' Collaboration. Variation in ischemic stroke frequency in Japan by season and by other variables. J Neurol Sci 2004; 225:85-9.

13. Miah AH, Sutradhar SR, Ahmed S, Bhattacharjee M, Alam MK, Bari MA, et al. Seasonal variation in types of stroke and its common risk factors. Mymensingh Med J 2012; 21:13-20.

14. Hannan MA, Rahman MM, Haque A, Ahmed HU. Stroke: seasonal variation and association with hypertension. Bangladesh Med Res Counc Bull 2001; 27:69-78.

15. Capon A, Demeurisse G, Zheng L. Seasonal variation of cerebral hemorrhage in 236 consecutive cases in Brussels. Stroke 1992; 23:24-7.

16. Oberg AL, Ferguson JA, McIntyre LM, Horner RD. Incidence of stroke and season of the year: evidence of an association. Am J Epidemiol 2000; 152:558-64.

17. Fang CW, Ma MC, Lin HJ, Chen CH. Ambient temperature and spontaneous intracerebral haemorrhage: a cross-sectional analysis in Tainan, Taiwan. Br Med J Open 2012; 8:2.

18. Shinkawa A, Ueda K, Hasuo Y, Kiyohara Y, Fujishima M. Seasonal variation in stroke incidence in Hisayama, Japan. Stroke 1990; 21:1262-7.

19. Gallerani M, Trappella G, Manfredini R, Pasin M, Napolitano M, Migliore A. Acute intracerebral haemorrhage: circadian and circannual patterns of onset. Acta Neurol Scand 1994; 89:280-6.

20. Rothwell PM, Wroe SJ, Slattery J, Warlow CP. Is stroke incidence related to season or temperature Lancet 1996; 347:934-6.

21. Strong K, Mathers C, Bonita R. Preventing stroke: saving lives around the world. Lancet Neurol 2007; 6:182-7.

22. Turin TC, Kita Y, Rumana N, Murakami Y, Ichikawa M, Sugihara H, et al. Stroke case fatality shows seasonal variation regardless of risk factor status in a Japanese population: 15-year results from the Takashima Stroke Registry. Neuroepidemiol 2009; 32:53-60.

23. Kumar P, Kumar A, Pandit AK, Pathak A, Prasad K. Seasonal Variations in Stroke: A Study in a Hospital in North India. Stroke 2015; 17:219-20.

24. Anlar O, Tombul T, Unal O, Kayan M. Seasonal and environmental temperature variation in the occurrence of ischemic strokes and intracerebral hemorrhages in a Turkish adult population. Int J Neurosci 2002; 112:959-63.

25. Dawson J, Weir C, Wright F, Bryden C, Aslanyan S, Lees K, et al. Associations between meteorological variables and acute stroke hospital admissions in the west of Scotland. Acta Neurol Scand 2008; 117:85-9.

26. McDonald RJ, McDonald JS, Bida JP, Kallmes DF, Cloft HJ. Subarachnoid hemorrhage incidence in the United States does not vary with season or temperature. AJNR Am J Neuroradiol 2012; 33:1663-8.

27. Keatinge WR, Coleshaw SR, Cotter F, Mattock M, Murphy M, Chelliah R. Increases in platelet and red cell counts, blood viscosity, and arterial pressure during mild surface cooling: factors in mortality from coronary and cerebral thrombosis in winter. Br Med J 1984; 289:1405-8.

28. Morabito M, Crisci A, Vallorani R, Modesti PA, Gensini GF, Orlandini S. Innovative approaches helpful to enhance knowledge on weather-related stroke events over a wide geographical area and a large population. Stroke 2011; 42:593-600.

29. Kelly-Hayes M, Wolf PA, Kase CS, Brand FN, McGuirk JM, D'Agostino RB. Temporal patterns of stroke onset: The Framingham Study. Stroke 1995; 26:1343-7.

30. Takizawa S, Shibata T, Takagi S, Kobayashi S. Japan Standard Stroke Registry Study Group. Seasonal variation of stroke incidence in Japan for 35631 stroke patients in the Japanese Standard Stroke Registry, 1998-2007. J Stroke Cerebrovasc Dis 2013; 22:36-41.

31. Passero S, Reale F, Ciacci G, Zei E. Differing temporal patterns of onset in subgroups of patients with intracerebral hemorrhage. Stroke 2000; 31:1538-44.

32. Woodhouse PR, Khaw KT, Plummer M. Seasonal variation of blood pressure and its relationship to ambient temperature in an elderly population. J Hypertens 1993; 11:1267-74.

33. Gordon DJ, Hyde J, Trost DC, Whaley FS, Hannan PJ, Jacobs DR, et al. Cyclic seasonal variation in plasma lipid and lipoprotein levels: the Lipid Research Clinics Coronary Primary Prevention Trial placebo group. J Clin Epidemiol 1988; 41:679-89.

34. Stout RW, Crawford V. Seasonal variations in fibrinogen concentrations among elderly people. Lancet 1991; 338:9-13.

35. Wilhelmsen L, Swardsudd K, Korsan-Bengtsen K, Larsson B, Welin L, Tibblin G. Fibrinogen as a risk factor for stroke and myocardial infarction. N Engl J Med 1984; 311:501-5.

36. Wang Y, Levi CR, Attia JR, D'Este CA, Spratt N, Fisher J. Seasonal variation in stroke in the Hunter Region, Australia: a 5-year hospital-based study, 1995-2000. Stroke 2003; 34:1144-50.

37. Klimaszewska K, Kulak W, Jankowiak B, Kowalczuk K, Kondzior D, Baranowska A. Seasonal variation in ischaemic stroke frequency in Podlaskie Province by season. Adv Med Sci 2007; 52:112-4.

38. Kim HJ, Kim JH, Kim DR, Kang HI, Moon BG, Kim JS. Age and meteorological factors in the occurrence of spontaneous intracerebral hemorrhage in a metropolitan city. J Cerebrovasc Endovasc Neurosurg 2014; 16:209-15.

39. Forti P, Maioli F, Procaccianti G, Nativio V, Lega MV, Coveri M, et al. Independent predictors of ischemic stroke in the elderly: prospective data from a stroke unit Neurology 2013; 80:29-38.

40. Saposnik G, Black S. Stroke in the very elderly: hospital care, case fatality and disposition. Cerebrovasc Dis 2009; 27:537-43.

41. Boutayeb A, Derouich M, Boutayeb W, Lamlili MEN. Cerebrovascular diseases and associated risk factors in WHO Eastern Mediterranean countries. Cardiol Angiol, 2014; 2:62-75.

42. Mouradian MS, Majumdar SR, Senthilselvan A, Khan K, Shuaib A. How well are hypertension, hyperlipidemia, diabetes, and smoking managed after a stroke or transient ischemic attack Stroke 2002; 33:1656-9.
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Publication:Journal of Postgraduate Medical Institute
Article Type:Report
Geographic Code:9PAKI
Date:Sep 30, 2015

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