Screening Tests to Diagnose Stroke Early: Guidelines and Criteria

Early diagnosis and prompt treatment of a stroke make that difference between death, disability and an active life. It can vastly improve the outcome and prognosis and help prevent its serious complications.

The emergency department is where the patient is first brought and it is this department, which initiates the immediate procedures to diagnose stroke.

The diagnosis just does not include the identification of this condition, but it has to differentiate the type of stroke, whether ischemic or hemorrhagic. Only then, the correct treatment can be given.

The criteria of the guidelines to diagnose stroke include:

  • Medical history helps to know whether you are harboring any risk factors that make you prone to suffer from a stroke. You should read the above linked post, which will give you a picture of why history taking is important in detecting a stroke.
  • Physical examination includes a detailed neurological examination to assess sensory neuron and motor responses, especially the reflexes, to find out whether the nervous system is affected.
  • Laboratory blood tests
  • Imaging tests such as MRI or CT scan of the brain
  • Other diagnostic tests that may be needed

The guidelines include interventions during the acute stage of the stroke (‘acute stroke’) or transient ischemic attack (TIA).

Most investigations are carried out during the first 48 hours after onset of symptoms, though some may be carried out even two weeks later.

Stroke differential diagnosis and mimics

The most common stroke mimics with their incidence include the following:

  • Seizure (17%)
  • Systemic infection (17%)
  • Brain tumor (15%)
  • Toxic-metabolic disorders, such as hyponatremia and hypoglycemia (13%)
  • Positional vertigo (6%)
  • Conversion disorder

Among these, hypoglycemia is the most common condition that can mimic a stroke and it can be readily detected and treated.

Clinical diagnosis by signs and symptoms

History and physical examination remain the basics of diagnosing a stroke.

Symptoms and signs can at times mislead the medic in diagnosing stroke; a proper history and physical examination are important.. It may be impossible to distinguish intracerebral hemorrhage from ischemic stroke from symptoms alone.

Therefore, the doctor has to be very thorough in following the diagnostic guidelines.

This face arm speech test examines for clinical features of facial and arm weakness, and  speech disturbance, which helps in quick and accurate identification of stroke,

Ischemic stroke

The most common features of an ischemic stroke are its acute onset, focal weakness and speech disturbance.

Hemorrhagic stroke

The following clinical findings are more typical of hemorrhagic stroke:

  • Coma (likelihood ratio
  • Neck stiffness
  • Seizures accompanying the neurologic deficit
  • Diastolic blood pressure >110 mm Hg
  • Vomiting
  • Headache

An acute onset of neurological symptoms, altered level of consciousness or mental status, or coma is seen more commonly with hemorrhagic stroke rather than with ischemic stroke.
Again, seizures are more common in an hemorrhagic stroke and are seen to occur in about 28% of such cases. They generally set in at onset of the intracerebral hemorrhage or within the first 24 hours.

Subarachnoid hemorrhage

Subarachnoid hemorrhage presents most commonly with severe headache. Furthermore, diagnosis of subarachnoid hemorrhage may require analysis of cerebrospinal fluid (CSF) when neuroimaging is not definitive.

Testing procedures to diagnose stroke

The diagnostic tests give an idea about how the brain appears, how it works and outlines the area of brain injury. Diagnostic tests fall into three categories.

  • Laboratory blood tests should include a complete blood count, a metabolic panel, and coagulation studies in patients taking anticoagulants. Coagulation studies include prothrombin time or international normalized ratio [INR] and an activated partial thromboplastin time.
  • Imaging tests show the brain picture similar to X-rays. The definitive test to distinguish ischemic stroke from hemorrhagic stroke is neuroimaging.
  • Electrical tests record the electrical impulses of the brain.
  • Blood flow tests show any changes in blood flow to and in the brain.

Imaging tests

Neuroimaging is the process that produces images of the brain structure and activity or any other part of the nervous system by magnetic resonance imaging (MRI) or computerized tomography (CT).

These procedures help to differentiate ischemic stroke from intracerebral hemorrhage, as well as to rule out other stroke mimics.

MRI v/s CT scan in stroke diagnosis

The choice of the neuroimaging procedures depends on the eligibility for acute stroke interventions,

MRI uses a large magnetic field to produce an image of the brain. It can detect changes in brain tissue and damage to brain cells from a stroke. It shows the location and extent of brain injury as does the CT scan.

However, the image produced by MRI is sharper and more detailed than a CT scan so it’s often used to diagnose small and deep injuries.

An MRI may be used alone or in addition to a CT scan to diagnose a stroke.

According to the new guideline published in the July 13, 2010, issue of Neurology, the medical journal of the American Academy of Neurology, diffusion MRI is more useful than a CT scan to diagnose acute ischemic stroke within the initial 12 hours of the first stroke symptom.

In one large study, MRI accurately diagnosed stroke 83 percent of the time versus 26 percent of the time by CT.

You may also have an angiogram, CT angiogram, or MRI angiogram to identify, which blood vessel is blocked or bleeding.

You should know that a stroke may show changes on these tests, but a mini stroke (TIA) will not.

Electric activity tests

Two basic tests, Electroencephalogram (EEG) and Evoked Response, show the brain’s electrical activity.

An EEG is a test that measures and records the electrical activity of your brain. Special sensors called electrodes are attached to your scalp.

The electrodes are connected by wires to a computer, which records your brain’s electrical impulses on the screen and prints them out as brain waves.

An Evoked Response test measures how the brain handles sensory impulses such as those related to hearing, sensation or vision.

Blood flow tests

Most blood flow tests make use of the ultrasound technology. It may be either a plain arterial ultrasound or an angiography with the help of an injected contrast dye.

Arterial angiography

An arterial ultrasound of the suspect artery is carried out by placing the probe over the artery, which may be the carotid artery in the neck or the vertebral artery at the base of the skull.

The ultrasound test measures the amount of blood flowing through the artery.

Besides the arterial ultrasound, there are other types of blood flow tests namely B-mode imaging, Doppler ultrasound and duplex scanning.

All these tests tell you about the condition of the arteries investigated, and about the blood flow through the artery — such as about the presence of a plaque within the arterial lumen, which can block an artery or narrow its lumen.

The Doppler ultrasound is a more specialized test that can also, in addition, give information about the speed and the direction of the blood flow.

Cerebral angiography

Cerebral angiography, also referred to as arteriography or arteriogram, is a medical procedure in which a radio-opaque contrast dye is injected into the arteries of the brain and its movements viewed on the screen.  X-rays are taken to view the movement of the dye through the suspect artery.

This procedure is also used to study blood flow in the cardiac arteries in heart conditions such as heart attack. There, it is called cardiac angiography.

Angiography shows the movement of the dye as it works its way through the cerebral blood circulation. Any abnormalities such as blockages, aneurysms or malformed blood vessels are easily diagnosed and viewed.

It also gives the size and location of the blockage or hemorrhage, which is of great help in confirming the diagnosis of an ischemic stroke and hemorrhagic stroke.

In some patients with cerebrovascular disease, conventional angiography has been replaced by magnetic resonance angiography (MRA) because it is a noninvasive test and permits the visualization of blood flow without the need for catheters or contrast agents.