Researchers have known for quite some time that there is a link between the gut and the brain. In more recent years, researchers have made a connection between proteins known as alpha-synuclein and Parkinson’s Disease (PD). This protein is found in the gastrointestinal tract (including the appendix) of patients that have been diagnosed with the early stages of PD.1 Alpha-synuclein is also found in clumps called Lewy bodies, which are found in the brains of patients with PD.
In October 2018, a study of over 1.6 million people in Sweden found that patients who had their appendix removed were less likely to develop PD, and patients who did develop PD were more likely to have a delayed onset.1 This outcome contradicted a 2016 Danish study which showed that patients who had an appendectomy (the surgery to remove the appendix) were slightly more likely to develop PD.
Most recently, researchers in the United States looked at the records of over 62 million patients from about 26 major health systems. Researchers identified patients who their appendix removed as well as patients who developed PD and looked for trends in these statistics. They found that in the almost 490,000 patients in the study who had an appendectomy, almost 4,500 developed PD (just under 1% of patients).2 Of the remaining 61.7 million people who did not have their appendix removed, only 0.29% developed PD (about 177,000 patients).2 This means that patients who had their appendix removed were 3 times more likely to develop PD than patients who didn’t have their appendix removed.1
The three times higher risk of developing PD was the same across age groups, genders, and races.1 However, because the records were de-identified, researchers were unable to draw any correlations between the appendix removal and the age of PD onset.2
Currently, no one is quite sure what the link is between the removal of the appendix and the onset of PD, but it is now fairly certain that there is some association between the two.1 While researchers are aware of this association, they caution that this is not a cause-and-effect finding, and right now they can only make educated guesses as to why patients who have appendectomies are more likely to develop PD. More research is needed to find a definitive cause.
Why did the studies have different outcomes?
One of the key differences between the Swedish study and the United States study was the length of time that patients were followed.3 The Swedish study followed patients for up to 52 years, where the US study only followed patients for up to 30 years. This is important as PD has what is known as a “prodromal period” which can last about 20 years.
During this prodromal period, PD patients may not experience classic movement and motor symptoms but may have less obvious symptoms, such as digestive issues which can lead to appendicitis (inflammation of the appendix, which is treated with an appendectomy).3 One of the theories about the correlation is that patients with prodromal PD are more likely to get appendectomies, but since they are not diagnosed yet, it makes the numbers look as though patients with appendectomies are more likely to develop PD.
More research is needed
As you can see, the correlation between appendix removal and PD is complex and not well understood. It is important to recognize that this research is still in the early stages and that researchers are working hard to identify how the appendix and PD are connected. Large population studies like the Swedish and US studies are important not because they give definitive answers, but rather because they ask questions that lead to better and more precise research. While conflicting research like this can be frustrating to PD patients and caregivers, it’s important because these studies help researchers look at diseases from many different viewpoints, which leads to innovation and better prevention, care and treatment for PD patients.
Paddock C. Study finds evidence of 'clear relationship' between appendectomy and Parkinson's. Medical News Today. https://www.medicalnewstoday.com/articles/325152.php. Published 2019. Accessed May 21, 2019.
Appendix removal associated with development of Parkinson's disease. EurekAlert!. https://www.eurekalert.org/pub_releases/2019-05/ddw-ara050619.php. Published 2019. Accessed May 21, 2019.
Saplakoglu Y. Another Study Found a Link Between Parkinson's Disease and the Appendix. What's Going On?. Live Science. https://www.livescience.com/65456-appendix-removal-parkinsons-risk.html. Published 2019. Accessed May 21, 2019.