Cerebral emboli are linked with Alzheimer's disease and vascular dementiaBMJ 2006; 332 doi: https://doi.org/10.1136/bmj.332.7550.0-c (Published 11 May 2006) Cite this as: BMJ 2006;332:0-c
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Paradoxical Cerebral Embolism As A Potential Cause of Alzheimer's Disease: Its Clinical Implications and a New Treatment of the Disease by Percutaneous Closure of a Patent Foramen Ovale
Until a few years ago, who would have thought that a patent foramen ovale (PFO) could have been the cause of migraine? Then it seems that there is indeed such an association . Ever since then, I have been waiting for somebody to come out with a paper saying that PFO may also be the cause of Alzheimer's disease. Now the interesting paper by Purandare et al  fulfills my prediction. In 32% of their patients with Alzheimer's disease in contrast to 22% of controls, a venous to arterial circulation shunt was detected by transcranial Doppler ultrasonography. Although the authors did not specify the site of the venoarterial shunt, it is presumed that such a right to left shunt took place via the PFO.
There is an existing debate as to whether every patient with migraine and a PFO should have the PFO closed percutaneously [3-12]. This form of therapy would impose a tremendous burden on the existing medical resources if such a policy were to be adopted. Alzheimer's disease is much more common than migraine; the clinical implication consequently would be far more significant.
Although the study by Purandare et al  seems to be fairly convincing, it is cross sectional and cannot be interpreted to show a cause and effect relation . Furthermore, one must bear in mind that patients with migraine are generally much younger than the patients with Alzheimer's disease. For young patients with a PFO and migraine, it is easier to be convinced of a cause-and-effect relation "paradoxical embolism"  than in older patients with a PFO and Alzheimer's disease who also may have other risk factors such as carotid or cerebral arteriosclerosis and atrial fibrillation. We need a much larger randomized controlled population study to tell us whether PFO can actually be responsible for Alzheimer's disease before recommending hundreds of thousands of patients with Alzheimer's disease to undergo percutaneous closure of their PFOs.
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Competing interests: No competing interests