A Closer Look at Cryptogenic Stroke

A Closer Look at Cryptogenic Stroke

A cryptogenic stroke (CS) is defined as cerebral ischemia of obscure or unknown origin. The cause of CS remains undetermined because the event is transitory or reversible, investigations did not look for all possible causes, or because some causes truly remain unknown. One third of the ischemic strokes are cryptogenic. Cryptogenic stroke is a diagnosis of exclusion — it is an ischemic stroke with no identifiable etiology.

The initial evaluation of any stroke includes a detailed history and examination, noncontrast CT scan of the head (to make sure there is no bleeding) and a 12-lead EKG. In addition, certain cardiac tests are routinely done such as telemetry (monitored in the EKG during hospitalization), 2-D echocardiogram, as well as some neurological tests such as a carotid Doppler and MRI.  If these can pinpoint the cause of the stroke, then no further workup would be needed.

However, as I have stated before, a third of ischemic strokes (no bleeding in the brain) do not have a definitive cause. This is especially true in people who are relatively younger (less than 60 years of age). In these patients, further workup is necessary. CS is most frequently due to cardiac embolism, followed by vasculopathy, and coagulopathy. The most frequent causes of cardiac embolism include paradoxical embolism from upstream veins via a patent foramen ovale (PFO), paroxysmal atrial-fibrillation, valvular heart-disease, and atrial septal aneurysm. The most frequent vascular causes of CS are complex aortic plaques and Fabry’s disease.  

Of these, the two most important and common are the presence of a patent foramen ovale and paroxysmal atrial fibrillation. I will discuss these in detail. A patent Foramen Ovale is a small hole in the heart. When the baby is in the mother’s womb, this is important for fetal circulation. Once the baby is born and takes normal breaths, this normally closes. However, in some people, this can stay partially open and will open with increased pressure on the right side of the heart, such as with straining or coughing. In these patients, this may be a source of a small blood clot from the legs being able to cross over to the left side of the heart and potentially go into the brain causing a stroke. This can be detected by a trans-esophageal echocardiogram where an echocardiogram is done with the probe in the esophagus. The patient is usually given sedation and some anesthesia. The doctor will use microbubbles to see if these can cross over.  If found, these small holes can be closed by an interventional/structural cardiologist without surgery and prevent strokes.

Atrial fibrillation is an irregular heart rhythm that is a fairly common cause of stroke.  In some patients, this is not present all the time. This makes it difficult to make the diagnosis. These patients will need some kind of monitoring to catch it. The most common way of doing this is with an internal loop recorder, a small device placed under the skin on the left side of the chest. This monitors the heart rhythm.  If detected, the treatment would be with blood thinners. This way, the patient can have the internal loop recorder for 6 months to a year to try and document this arrhythmia.

Most strokes centers will have a cryptogenic stroke protocol so that the process of having these evaluations is easily done.

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