Depending on what statistic youâ€™re looking at anywhere from 30-40% of strokes result from an unknown cause.
Thatâ€™s right. A full work-up of these patients reveals no cardioembolic causes, no large-artery occlusive disease, and typically an absence of risk factors. Itâ€™s a diagnosis of exclusion and itâ€™s calledÂ cryptogenic.
So what actually causes these strokes to occur? Why does a clot form and occlude a vessel if there are no known reasons for it to do so?
Thereâ€™s a couple of theories (presently more like a collection of correlations):
1.Â Patent Foramen Ovale.Â PFO has been been shown to have an increased incidence in patients who suffer cryptogenic strokes. PFO is present in 17-35% of the general population but is witnessed in up to 45% of cryptogenic stroke patients. (Source)
2.Â Pathogenic/Immune Response.Â Thereâ€™s a growing body of epidemiological studies indicating a correlation between receiving an annual flu vaccine and a pretty significant decrease in stroke & heart attacks. (Source)
3.Â Subclinical Atrial Fibrillation. In one study (n=51; be wary of the small sample size) where patients wore a type of implantable arrhythmia detector A-fib was detecting in 25% of the subjects. The mean detection date was at Day 48 representing a very infrequent onset. Paroxysmal A-fib like is would be incredibly difficult to detect as it is so transient. (Source)
4.Â Undetected Genetic and/or Environmental Causes and/or Some Other Unknown. Research into environmental causes of neurological pathology is a pretty hot area of research and when it comes to genetics (and epigenetics) we are barely scratching the surface.