Sometimes, even with testing, the underlying cause of a stroke can’t be identified. When this happens, the stroke is classified as a cryptogenic stroke. These strokes make up about 25–40% of ischemic strokes.

Nearly 800,000 people have a stroke each year in the United States. The two main types of strokes are called ischemic strokes and hemorrhagic strokes.

Ischemic strokes make up about 87% of strokes. They occur when a blood vessel in your brain becomes blocked, usually by a blood clot.

Hemorrhagic strokes are less common. They occur when a blood vessel ruptures, which can cause bleeding in your brain.

A stroke is called “cryptogenic” when the cause can’t be determined. Doctors classify strokes as cryptogenic in the following situations:

  • they can’t find the cause of the stroke
  • the stroke has two or more possible causes
  • the cause of the stroke hasn’t been fully evaluated

Read on to learn more about cryptogenic strokes, including how they’re diagnosed and treated.

Most strokes are ischemic and are caused by a blood clot that disrupts blood flow to part of your brain. Sometimes, even with testing, the cause of a stroke can’t be identified. In this case, the stroke is classified as cryptogenic.

It’s thought that a large proportion of cytogenic strokes are caused by:

  • Atrial fibrillation (AFib): Atrial fibrillation (AFib) is a type of irregular heartbeat that increases your risk of stroke more than 5 times.
  • Hypercoagulable state: A hypercoagulable state occurs when your blood is more prone than usual to forming blood clots.
  • Aortic arch atheroma: Aortic arch atheroma is a build-up of plaque inside the top of the main artery that leads away from your heart. A piece of this plaque can break off and reach your brain.
  • Patent foramen ovale: Patent foramen ovale is a hole in your heart, present from birth, that doesn’t close entirely as you get older. This condition is present in about 25% of adults and usually doesn’t cause problems.
  • Other causes: rarer causes of cryptogenic stroke include:
    • a tear in the wall of one of your arteries
    • cancer

Cryptogenic strokes make up 25–40% of ischemic strokes. It’s estimated that there are more than 240,000 each year in the United States.

According to the American Stroke Association (ASA), some evidence suggests that people of African American descent are twice as likely and Hispanic Americans are about 46% more likely of having a cryptogenic stroke.

Symptoms of a stroke can vary depending on what area of the brain is affected. Common symptoms include:

  • severe headache
  • dizziness
  • loss of balance
  • lack of coordination
  • vision changes or trouble seeing
  • sudden confusion
  • sudden difficulty speaking or understanding speech
  • sudden paralysis, numbness, or weakness on one side of your body, including the:
    • face
    • arms
    • legs

Learn more about stroke symptoms.

When to seek emergency medical attention

It’s critical to seek immediate medical attention, by calling 911 or local emergency services, if you believe you or someone you’re with is having a stroke. The faster treatment begins, the lower the risk of permanent brain damage will be.

Treatment is usually most effective if it’s initiated within 3 hours of when the first symptom began.

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According to the ASA, as many as 1 in 4 people who survive a stroke will have another. Identifying the cause of the stroke helps doctors provide the proper treatment and reduces the risk of another stroke in the future.

Doctors use many different tests to evaluate cryptogenic strokes and to look for the underlying cause.

An initial examination after your stroke usually includes:

  • review of your medical history
  • a physical exam
  • noncontrast CT scan of your head
  • 12-lead electrocardiogram, a painless test that measures the electrical activity of your heart

Further tests may be performed to examine the function of your heart and to look at the blood vessels in your brain.

Heart tests may include:

Imaging tests may include:

Additional tests that are performed on some people include:

  • assessment for hypercoagulability (thick blood)
  • artery and blood vessel disease tests
  • cancer screening

Antiplatelet or anticoagulation therapy is recommended for nearly all people who have had a cryptogenic stroke. These medications help prevent or break up blood clots that form in your blood vessels.

People who have certain health conditions, such as a blood disorder, diabetes, high blood pressure, or other conditions, may not be eligible for this treatment.

Antiplatelet therapy involves taking medications that stop blood cells, called “platelets,” from sticking together. Anticoagulation medications alter the proteins involved in the blood clotting process.

Finding the underlying cause of a stroke is important because it helps doctors know which type of treatment is most likely to be effective at preventing another stroke in the future. For example, cryptogenic strokes caused by AFib are more effectively treated with anticoagulation medications than antiplatelets.

What can you do to reduce your risk of another stroke?

According to a 2017 review, the 2-year reoccurrence rate of a cryptogenic stroke is quite high, around 14–20%. Certain lifestyle changes may help reduce the risk of reoccurrence, including:

You may also be able to reduce your risk of another stroke by managing other underlying health conditions if you have them, such as:

A transient ischemic attack (TIA) occurs when blood flow in your brain is temporarily disrupted. A TIA is also called a “ministroke.” TIAs can cause stroke-like symptoms, but the symptoms are temporary and typically last from a few minutes up to 24 hours.

A TIA isn’t the same as a cryptogenic stroke, but if you have a TIA with an unknown cause, the doctor may refer to it as a “cryptogenic TIA.”

Even though the symptoms may not last long, it’s very important to get immediate medical attention if you suspect you or somebody you know has had a TIA. Diagnosing and treating the underlying cause of a TIA may help lower the risk of a more serious stroke in the future.

A cryptogenic stroke is a stroke that has no identifiable cause. These strokes make up about 25–40% of ischemic strokes.

The symptoms of a cryptogenic stroke may include weakness or paralysis on one side of the body, dizziness, coordination issues, trouble speaking, and confusion.

It’s important to get immediate medical attention if you have any of these symptoms. The sooner you can get treatment, the higher the likelihood there is of a positive outcome.

To avoid another stroke in the future, it’s important that health professionals are able to diagnose the underlying cause of a stroke and prescribe the right treatment and preventive measures.