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When a stroke occurs, identifying what caused it is important to help prevent recurrence. However, in some cases, the cause isn’t immediately obvious. A stroke with an unknown cause is a cryptogenic stroke.

When someone has a cryptogenic stroke, they should undergo further testing to determine the potential cause. That way, they can get treatment that can help prevent them from having another stroke in the future.

“Many times, for the patients whose strokes end up being classified as cryptogenic, we’re still trying to figure out the cause on the outpatient basis,” says Matthew Starr, MD, associate director, UPMC Stroke Institute. “One of the main reasons we want patients to follow up after their stroke hospitalization is we can make sure that we’ve done our best to rule out other causes or to try to determine the etiology for their stroke.

“If you figure out the etiology, then you can decide what are the best medicines to try to prevent another event.”

Learn more about cryptogenic strokes and how to manage them.

Types of Strokes

About 800,000 Americans have a stroke each year. There are two major types:

• Hemorrhagic stroke — A hemorrhagic stroke happens when a blood vessel in the brain ruptures, causing blood to spill into the brain.
• Ischemic stroke — An ischemic stroke occurs when a clot develops in a blood vessel that supplies blood to the brain, restricting blood flow. The clot can either happen in the brain or somewhere else in the body and travel to the brain. More than 85% of strokes are ischemic.

When strokes occur, the brain can’t get its normal amount of blood and oxygen. This causes brain cells to die. Stroke is the leading cause of disability in American adults and one of the top causes of death in the United States.

What Is a Cryptogenic Stroke?

A cryptogenic stroke is an ischemic stroke when the cause isn’t initially known.

When a patient comes to the hospital for a stroke, they undergo a wide range of tests to determine the cause. This can include imaging of the brain, heart, and blood vessels, heart monitoring, and blood work.

Sometimes, the cause isn’t apparent even after testing. In those cases, the stroke is cryptogenic.

About 30% of ischemic strokes are cryptogenic, Dr. Starr says. They’re more likely in younger people, he says.

Sometimes, further testing can eventually reveal the stroke’s cause. Other times, it never determines the cause.

“There are some cases where, with further longitudinal workup, we’re able to discover what the cause is,” Dr. Starr says. “Then there are some strokes that are truly cryptogenic where we don’t ever find the cause. And in those situations, we do our best to rule out other causes.”

What Causes Cryptogenic Strokes?

Potential causes of cryptogenic strokes include:

• Atrial fibrillation (AFib) — AFib is an abnormal heart rhythm that occurs when the top two chambers of the heart (the atria) beat irregularly. People with AFib often have a very fast heartbeat. AFib can cause a clot to form that travels to the brain.
• Blood clotting disorders — Also known as a hypercoagulable state or thrombophilia, these are conditions wherein the blood clots more easily.
• Mild carotid stenosis — Carotid stenosis occurs when plaque builds up and narrows the carotid arteries, which bring blood to the brain. Severe carotid stenosis — a narrowing of above 50% — is often the pinpointed cause of a stroke. However, more mild narrowing is another possible cause.
• Patent foramen ovale (PFO) — A PFO is a small hole between the top chambers of the heart. This hole is present as all babies develop before birth; it’s supposed to close shortly after birth. In about 25% of people, the hole never closes, and the foramen ovale remains patent, or open. If a clot develops in the venous system, then it could go across the PFO, travel to the brain, and cause a stroke.

Less common causes of cryptogenic stroke can include clotting caused by cancer, infections, and more.

How Are Cryptogenic Strokes Managed?

If a patient’s stroke is cryptogenic, they may undergo further testing to determine a possible cause.

Because AFib is a common cause of stroke, doctors may prescribe a device that measures their heart rhythm. This can include an external device such as a Holter monitor or, in some cases, an implantable device. The batteries in an implantable device can last for up to three years, allowing for long-term monitoring for AFib.

“Sometimes, a patient will come into the hospital, and we won’t find atrial fibrillation in the hospital,” Dr. Starr says. “Then, we’ll have them wear a heart monitor, and we’ll find it when they’re out of the hospital. And if atrial fibrillation is found on their monitor, the stroke is not cryptogenic anymore.”

Doctors also may do further blood work and imaging tests to look for other possible causes.

Follow-up care can either reveal the cause of a cryptogenic stroke or help people manage their health so they can avoid another stroke.

“There’s 800,000 strokes a year. Of that number, probably 200,000 are recurrent events — so, someone who’s had a stroke before having a second event,” Dr. Starr says. “There’s a big number that we could be stomping out if we could find the cause.”

Treating Cryptogenic Strokes

Treatment for cryptogenic strokes can help reduce the risk of another stroke.

• Aspirin — Aspirin can prevent strokes that AFib didn’t cause. If a patient has a cryptogenic stroke, their doctor may recommend they take aspirin.
• Blood thinners — Blood-thinner medications can help to prevent blood clots. If further testing of a patient with a cryptogenic stroke reveals AFib, their doctor will likely prescribe a blood thinner.
• Closing a PFO — If a patient with a cryptogenic stroke has a PFO, their doctor may refer them to a cardiac surgeon. A minimally invasive catheter-based procedure can close the PFO.
• Lifestyle changes — Making lifestyle changes like eating healthier, exercising regularly, and quitting smoking can reduce risk factors for stroke. These can include high blood pressure, high cholesterol, and diabetes.

The UPMC Stroke Institute specializes in the management and care of patients who have a stroke. UPMC’s experts work to diagnose and treat strokes with state-of-the-art approaches.

Dr. Starr oversees UPMC’s Cryptogenic Stroke Clinic, where his team provides ongoing care for patients with cryptogenic strokes. He urges patients diagnosed with cryptogenic strokes to seek follow-up care.

“For patients who have strokes where we don’t know the answer, I tell them: ‘We don’t know what caused your stroke yet. We want you to come and see me in the clinic, and we’ll do some more tests and review what’s happened so far and see if something has shown up’” Dr. Starr says.

“So, I just try to have a conversation with them to say we’re still trying to get to the bottom of this.”