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September 20, 2012

Stroke: Causes, Treatment & Prevention

Credit: National Center for Chronic Disease Prevention and Health Promotion, Division for Heart Disease and Stroke Prevention

What is Stroke?

A Stroke, sometimes referred to as cerebrovascular accident (CVA), is the rapid loss of brain function due to a disturbance in the blood supply to the brain. This can be due to ischemia (lack of blood flow) caused by blockage (thrombosis, arterial embolism), or a haemorrhage (internal bleeding or loss of blood that occurs from the vascular system into a body cavity). As a result, the affected area of the brain cannot function, which might result in an inability to move one or more limbs on one side of the body, inability to understand or formulate speech, or an inability to see one side of the visual field. A stroke is a medical emergency and if untreated, it can cause permanent neurological damage and death.

Classification


Stroke can be classified into two major categories: ischemic and haemorrhagic. Ischemic strokes are those that are caused by interruption of the blood supply, while haemorrhagic strokes are the ones which result from rupture of a blood vessel. About 87% of strokes are caused by ischemia and the remainder by haemorrhage.

In an ischemic stroke, blood supply to part of the brain is decreased, leading to dysfunction of the brain tissue in that area. There are four reasons why this might happen:

  • Thrombosis (obstruction of a blood vessel by a blood clot forming locally)
  • Embolism (obstruction due to an embolus from elsewhere in the body)
  • Systemic hypo perfusion (general decrease in blood supply, e.g., in shock)

Stroke without an obvious explanation is termed “cryptogenic” (of unknown origin); this constitutes 30-40% of all ischemic strokes.

What are the symptoms of Stroke?


Stroke can exhibit the following signs and symptoms.

  • Loss of consciousness, headache, and vomiting usually occur more often in haemorrhagic stroke than in thrombosis because of the increased intracranial pressure from the leaking blood compressing the brain.
  • Sudden-onset face weakness, arm drift (i.e., if a person, when asked to raise both arms, involuntarily lets one arm drift downward) and abnormal speech
  • Stroke symptoms appear suddenly, over seconds to minutes, and in most cases do not progress further.
  • In most cases, the symptoms affect only one side of the body (unilateral). Depending on the part of the brain affected, the defect in the brain is usually on the opposite side of the body
  • The symptoms depend on the area of the brain affected. The more extensive the area of brain affected, the more functions that are likely to be lost.

If the area of the brain affected contains one of the three prominent central nervous system pathways—the spinothalamic tract, corticospinal tract, and dorsal column (medial lemniscus), symptoms may include:

  • hemiplegia and muscle weakness of the face
  • numbness
  • reduction in sensory or vibratory sensation
  • initial flaccidity (hypotonicity), replaced by spasticity (hypertonicity), hyperreflexia, and obligatory synergies

A stroke affecting the brain stem and brain therefore can produce symptoms relating to deficits in cranial nerves like,

  • altered smell, taste, hearing, or vision (total or partial)
  • drooping of eyelid (ptosis) and weakness of ocular muscles
  • decreased reflexes: gag, swallow, pupil reactivity to light
  • decreased sensation and muscle weakness of the face
  • balance problems and nystagmus
  • altered breathing and heart rate
  • weakness in sternocleidomastoid muscle with inability to turn head to one side
  • weakness in sternocleidomastoid muscle with inability to turn head to one side

If the cerebral cortex is involved, the CNS pathways can again be affected, but also can produce the following symptoms:

  • aphasia (difficulty with verbal expression, auditory comprehension, reading and/or writing)
  • dysarthria (motor speech disorder resulting from neurological injury)
  • apraxia (altered voluntary movements)
  • visual field defect
  • memory deficits (involvement of temporal lobe)
  • disorganized thinking, confusion, hypersexual gestures (with involvement of frontal lobe)

If the cerebellum is involved, the patient may have the following:

  • altered walking gait
  • altered movement coordination
  • vertigo and or disequilibrium

Causes of Stroke


The cause of stroke varies with age, comorbidity and the clinical presentation as well.

  • Thrombotic stroke caused by large vessel disease or small vessel disease
  • Sickle-cell anemia, which can cause blood cells to clump up and block blood vessels, can also lead to stroke. A stroke is the second leading killer of people under 20 who suffer from sickle-cell anemia
  • Embolic stroke which has atrial fibrillation as a cause
  • Systemic hypoperfusion or the reduction of blood flow to all parts of the body. It is most commonly due to heart failure from cardiac arrest or arrhythmias, or from reduced cardiac output as a result of myocardial infarction, pulmonary embolism, pericardial effusion, or bleeding
  • Cerebral venous sinus thrombosis
  • Intracranial hemorrhage caused by trauma, bleeding disorders, amyloid angiopathy, illicit drug use
  • A silent stroke is a stroke that does not have any outward symptoms, and the patients are typically unaware they have suffered a stroke.
  • Non-modifiable risk factors including genetic predisposition, age, gender
  • Metabolic risk factors including atrial fibrillation, hypertension, dyslipidemia, diabetes mellitus, disorders affecting the blood coagulation
  • Socio-behavioral risk factors including unhealthy diet, physical inactivity, unhealthy personal habits (Alcohol use could predispose to ischemic stroke) and stress. he drugs most commonly associated with stroke are cocaine, amphetamines causing hemorrhagic stroke

Diagnosis of Stroke


Stroke is diagnosed through several techniques: a neurological examination (such as the NIHSS), CT scans (most often without contrast enhancements) or MRI scans, Doppler ultrasound, and arteriography. A physical examination, including taking a medical history of the symptoms and a neurological status, helps giving an evaluation of the location and severity of a stroke. It can give a standard score on e.g., the NIH stroke scale.

  • Given the disease burden of stroke,prevention is an important public health concern. Because stroke may indicate underlying atherosclerosis, it is important to determine the patient’s risk for other cardiovascular diseases such as coronary heart disease.
  • Conversely, aspirin confers some protection against first stroke in people who have had a myocardial infarction or those with a high cardiovascular risk.
  • In those who have previously had a stroke, treatment with medications such as aspirin, clopidogrel and dipyridamole may be given to prevent platelets from aggregating.
  • Lifestyle modification retains the highest priority among other preventive strategies. As saturated fat and dietary cholesterol are dietary risk factors, their intake within the optimal levels may prove beneficial. As dietary polyunsaturated fatty acids have anticoagulant effects, their regular intake in recommended amounts is vital. Physical activity can alleviate the ill-effects of metabolic risk factors. Smoking cessation, reduced alcohol intake, stress management are other preventive strategies based on subjective risk.
  • Carotid endarterectomy or carotid angioplasty can be used to remove atherosclerotic narrowing (stenosis) of the carotid artery.
  • Anticoagulation can prevent recurrent ischemic strokes. Among patients with nonvalvular atrial fibrillation, anticoagulation can reduce stroke by 60% while antiplatelet agents can reduce stroke by 20%
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James Watson
Xcode is a pioneer in personal genomics, focussed on enabling personalized preventive healthcare. We are dedicated to empowering physicians, wellness professionals and customers with the most validated, accurate and actionable genomic information to positively impact and improve their client's health and quality of life.