Stroke Risk Factors

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Learning objectives

  • What are the main stroke risk factors ?
  • What does it do and clinical effects of damage ?
  • How do I manage these ?

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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.

Definitions

  • Absolute risk: Risk in absolute numbers e.g. 1 per 100 persons in group A will have a stroke in the next year and 1 in 200 will have a stroke in the next year in Group B
  • Relative Risk: The ratio of risks of Group A with respect to Group B e.g. Group B has a 50% or 0.5 relative risk compared with group A. Moving from Group B to Group A gives a relative risk increase of 2. This is much misused as an intervention that reduces risk from 1 in 5,000 to 1 in 10,000 or by half or 50% or 0.5 may not be worth even the low risks of the intervention.
  • Odds Ratio: risk of having stroke if having disease x divided by risk of having disease when patient does not have disease x
  • Hazard ratio:

Stroke Risk Factors

Non-Modifiable Stroke Risk Factors
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-olds 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 1.2-1.3) really until age > 75 when the balance between sexes tends to reduce and equalise in old age. Stroke commoner in females mainly because they live longer.
Birth Weight There is an association between stroke in Adulthood and low birth weight.
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 atherosclerotic disease. There can also be differences in diagnostic rates and management and stroke prevention in those of different races.
Genetic historyA number of genetic diseases predispose to a greater incidence of stroke. CADASIL, Sickle cell, Ehlers-Danlos syndrome, Homocystinuria etc.
Previous StrokeHaving had a previous stroke or TIA places one in a higher risk group. The average yearly risk is 9% but that is over all stroke types and for some is much lower and others higher.
Modifiable Stroke Risk Factors
Hypertension (Systolic or diastolic) Odds ration ranges from 2.6 to 4 so hypertension is a major risk factor for both ischaemic and haemorrhagic stroke. This however varies with age. Both systolic and diastolic levels are important. Hypertension (Each 10 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.
Diabetes Mellitus increased by 2-6 times
AF/PAF or Atrial flutter Very powerful risk factors. See article. Use CHADsvaSC for risk scoring.
Valvular heart disease rheumatic mitral stenosis with AF hugely increases cardioembolic risk
Previous stroke or TIAThis is also a powerful risk factor for a further stroke. This includes both small vessel disease / white matter disease and old cortical infarcts.
Silent infarcts on ImagingThis is also a powerful risk factor for a further stroke. Odds ratio of about 2-3.
Diabetes Mellitus increased by 2-6 times
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. Risk tends to increase the more tight the stenosis is. Risk may be managed with good medical therapy and consideration of carotid endarterectomy.
DyslipidaemiaThe relationship is not as clear cut as with IHD. Stroke is commoner with elevated Cholesterol and LDL especially large vessel and atherosclerotic stroke and carotid disease. There may be a relationship between low cholesterol and intracerebral haemorrhage. Intense lipid lowering might increase risk of ICH.
Cigarette smoking increases stroke risk by 50% which is far less than the risk related to IHD. 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
Cardiac diseaseAF as has been discussed, mitral valve disease, PFO, atrial septal aneurysm, Cardiomyopathy, transmural MI, atrial myxoma, mechanical heart valve
Physical inactivity (increased risk by 2.5)
Excess alcohol Increases risk by 50-100%
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.