It’s not the most obvious thought: Look for early symptoms of a brain disease in the large intestine. Yet growing evidence shows this is exactly where to look for Parkinson’s disease, finding signs of it there years before the terrible trembling symptoms of the disease first appear. How did this come about?
Parkinson’s disease (PD) is named after British doctor James Parkinson who first described the condition in 1817. PD has been understood since the late 1800s as a disease of the central nervous system. Autopsies of persons with PD have for decades been known to contain distinct abnormalities in parts of the brain producing the important neurotransmitter called dopamine. These oddities are called Lewy bodies, for the doctor who first described them in 1913. But how to detect these abnormal signs of PD before the time of an autopsy?
Logically enough, doctors have used various kinds of medical imaging of the brain, attempting to capture a picture of Parkinson’s early warning signs. Unfortunately, computed tomography (CT) and magnetic resonance imaging (MRI) of PD patients’ brains appear normal. One type of brain imaging may aid in diagnosing PD if an abnormality is seen, but this is not an exclusive association. So, brain scans are mainly used to rule out other disorders that could cause similar symptoms but do show up in imaging, such as tumors and vascular abnormalities.
Doctors continue to diagnose Parkinson’s disease by clinical criteria such as slowness of movement, rigidity, tremors while a person is at rest, instability of movements and postural changes. They may also give a patient the most common PD medication, levodopa, and if their symptoms improve they are judged to have the disease. However PD undergoes a long process of slow development before any external symptoms appear, at which point patients with Parkinson’s disease will have lost 60% to 80% of the dopamine-producing cells in their brain. As with other diseases, earlier detection and treatment of PD might lead to better medication responses – essentially heading off PD before it can take a stronger hold. The problem has simply been a question of how to detect it early.
Now along comes the possibility of detection within the large intestine. Why did anyone even think of looking there to begin with? It’s because doctors have known for a long time that our gastrointestinal tracts are extremely rich in nerves. These nerves are connected to the central nervous system but continue to function even when their connection to it is cut. These millions of nerve cells and fibers surrounding the gut are called the enteric (intestinal) nervous system, and it is even sometimes called “the second brain.” Significantly for Parkinson’s disease, the enteric nervous system also produces the neurotransmitter dopamine.
As early as the 1930s, doctors found what looked like Lewy bodies in peripheral nerve clusters next to the spinal cord and leading to the enteric nervous system in patients with PD. This was rediscovered in the 1960s by Dutch scientists and various others since then. However it wasn’t clear if these were truly the same Lewy bodies as in the brain or just superficially resembled them. Then, in the 1990s, a brain protein called synuclein (sin-NUKE-lee-in) was discovered, and by the late 1990s it was clear that it was present in Lewy bodies. Since that time, researchers around the world have shown that Lewy bodies seen in gut nerves are the real thing and contain synuclein.
Doctors in Paris, France first showed in 2008 that synuclein can be detected in biopsies taken during colonoscopies, and various European centers have been pursuing this finding since then. It seems this approach was not widely known in the US until earlier this year when researchers at Rush Medical Center in Chicago also found evidence of PD in biopsy samples from colonoscopies and the similar but simpler procedure known as sigmoidoscopy. The most significant finding to date is that Lewy bodies can be found in the colon of PD patients several years before they show any other symptoms. At last, an early-warning marker in tissue that is much more easily obtained than a brain biopsy or autopsy!
This promising approach to early PD detection is not yet in common clinical practice, because it’s important to determine the best standardized way to go about such a test. Look for it to arrive in doctors’ offices in the coming years, however – and remember that you heard about it here first!
Colonoscopy.com provides people with a listing of available gastroenterologists in their area. Whether you’re looking for a virtual colonoscopy or sigmoidoscopy, you can find a doctor right for you.