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Risk Factors for Stroke


Learning objectives

  • Understand Risk factors
  • How they can help us assess risk of stroke and TIA
  • How they help us define management

Introduction

Stroke is often compared with ischaemic heart disease. The main risk factor for stroke disease is hypertension and for ischaemic heart disease is dyslipidaemia. However as stated elsewhere coronary artery disease is a single disease process centred around the development and rupture of atherosclerotic plaques. Stroke however is a mixture of at least 100 different disease aetiologies many of which may co-exist with mixed acquired and congenital risk factors. Therefore teasing out risk factors is far more difficult without trying to analyse different stroke subtypes using for example the TOAST classification. It should be clear that risks do not always infer causality. That needs a separate line of scientific proof. It is important as treating associations may not provide the same risk reduction as treating directly causal risks. Even now despite hypertension being the most overwhelming risk factor it is still unclear whether the risk comes from the absolute level or the degree of BP variability. There is much that we don't know.

Practically we discuss risk factors as modifiable - where an intervention with a suggested or proven causal risk will reduce the risk of stroke. This may be seen with managing hypertension, with total cholesterol, anticoagulation for AF, carotid surgery, physical inactivity, alcohol etc. Non-modifiable risks are gender, age, race, genetics etc.

The Interstroke study [1] showed that just a core of five risk factors accounted for more than 80% of the global risk of all stroke (ischaemic and intracerebral haemorrhagic): hypertension (x 3-4) Current smoking (x 2), abdominal obesity (x1.5), diet (1.35), and regular physical activity (0.69). Others included Diabetes (1.36), Alcohol (1-30 drinks/month) 0.9 but excess of this x 1.51, Psychosocial stress x 1.3, Cardiac causes x 2.38. ApoB to ApoA1 1.89. Targeted interventions that reduce blood pressure and smoking, and promote physical activity and a healthy diet, could substantially reduce the burden of stroke.

Stroke Risk FactorRelative risk and comments
Hypertension (Systolic or diastolic) increases risk x 2-4. Hypertension is a major risk factor for ischaemic and even more so for haemorrhagic stroke (x 9) . Hypertension (Each 100 mmHg diastolic or 20 mmHg systolic doubles stroke rate). It is not acute rises but chronic sustained elevations in blood pressures which damage deep penetrating arteries which occlude or bleed and in larger vessels accelerate atherosclerosis as well as causing cardiac damage and atrial fibrillation.
Age No age group is immune to stroke. There is even a baseline level of strokes in infants and children increasing gradually through all age groups with a steep rise in those over 75. Incidence doubles with every decade over 55. It is uncommon but any medium sized unit will see several 18-30 year old patients per year with stroke. Stroke is often the cause of death in the frail elderly.
Male gender Stroke is slightly more common in males ( x 1.2) really until age > 75 when the balance between sexes tends to reduce and equalise in old age.
Diabetes Mellitus increased by 2-6 times
Race All types of stroke is commoner in Blacks but especially ICH. Chinese, Asians and Blacks have an increased risk of ICH. Blacks and east Asians have an increased incidence of intracranial athersclerotic disease
AF/PAF or atrial flutter and sick sinus syndromeMajor modifiable risk factors. See CHADS2 or CHADSVASC scoring and consider anticoagulation to prevent ischaemic stroke
Valvular heart disease rheumatic mitral stenosis with AF hugely increases cardioembolic risk
Previous stroke or TIAThis is a significant risk factor
Carotid stenosis is itself a direct marker of an atherosclerosis process that can either result in throwing of emboli or occluding the carotid and causing ipsilateral infarction
Dyslipidaemia Stroke is commoner with elevated Cholesterol and LDL. The relationship is not as clear cut as with IHD. There may be a relationship between low cholesterol and intracerebral haemorrhage.
Current Cigarette smoking increases stroke risk by 50% which is far less than the risk related to IHD. Stronger link with ischaemic stroke. Cessation reduces ischaemic stroke.
Oral contraceptive and HRT Doubles the stroke risk for low oestrogen content and increased by four times for higher oestrogen content. Can increase risk of thromboembolic stroke and cerebral venous thrombosis and subarachnoid haemorrhage though the absolute risk is very low and pregnancy itself has stroke risks. Particularly concerning is the combination of OCP with other risk factors such as smoking and migraine with aura or thrombophilias
Family historyA family history of stroke at a young age might suggest a genetic cause e.g. Fibromuscular dysplasia, CADASIL etc. or a polygenic disorder such as hypertension.
Psychosocial stressMild increase in stroke risk by about x 1.3
Physical inactivity (increased risk by 2.5). Physical activity appears to be protective of both ischaemic ahd haenmorrhagic stroke.
Excess alcohol Increases risk by 50-100% once more than 30 drinks per month or binge drinking. Moderate alcohol appears protective. Relationship stronger for haemorrhage.
Obesity Often complex and hard to disentangle risks for instance it is suspected now that obesity itself is not a risk of itself but the increased stroke risk is due to additive risk from the increased diabetes and hypertension associated with the obesity. Still management is to address the obesity and lose weight.
Pregnancy and puerperium risk of stroke in the days before birth and the 6 weeks after is rare it is one of the commoner settings for stroke in young adults related possibly to a hypercoagulable state and vessel wall changes.
MigraineRecord whether migraine with aura or not. Migraine with aura appears to double stroke risk. Increased risk if under 45, smoking and on OCP. Mostly posterior circulation. Migraine also associated with dissections, Antiphospholipid syndrome, CADASIL and MELAS and Essential thrombcythaemia.
Polycythaemia HCT > 0.5 in males and 0.47 in females is associated with increased stroke risk
Antiphospholipid (aPL) antibodies found in autoimmune conditions and can be associate with stroke mainly in young females.
Illicit drugs Drugs with a sympathomimetic effects (amphetamine, cocaine, crack) can cause ischaemic stroke through several mechanisms such as acute hypertension, enhanced platelet aggregation, and rarely vasculitis (mainly related to amphetamine intake) of the polyarteritis nodosa or giant cell-granulomatous types.

References

  • [1]:Interstroke Investigators. Risk factors for Ischaemic and Intracerebral haemorrhagic stroke in 22 countries (the INTERSTROKE study): a case-control study. Lancet 2010: 376;112-23

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