OK, I’ll admit it…I nurse a small, irrational hope that some medical professional will say, “Your Parkinson’s diagnosis back in 2012 was incorrect — you actually have ….um…. .zatzsiosis, but it’s nothing to worry about.” Sorry — not only is zatzsiosis a disease I just made up, my neurologist is an excellent, experienced clinician who could reel off many symptoms that determined my PD diagnosis.
But there is no objective way to diagnose PD. I initially thought you just gave a blood sample or the like and they tested it for dopamine. Nope — that is why finding a biomarker for PD is one of the Holy Grails of PD research. Biomarkers are critical to verify you actually have PD, to measure how it progresses, and — another Holy Grail –to measure if XYZ Miracle Drug reverses the PD progression.
I recently heard a presentation by Charles Adler of the Mayo Clinic about the difficulties on diagnosing PD. There is presently one biomarker to confirm PD — unfortunately, you have to be dead. The biomarker is the presence of Lewy bodies (protein clumps) in your brain, which can only be determined by autopsy. Dr. Adler presented an autopsy study with the result that only 26% of patients with “possible Parkin” had it per the autopsy. In another autopsy study, experts were only correct 80-90% of the time with diagnosis. For patients determined to be “possible PD” on first visit, and who had a PD diagnosis for 5 years or less at time of death, only about 50-60% had PD per autopsy.
Complicating PD diagnosis, non-motor symptoms can show up years before the motor symptoms that most laypeople associate with PD (e.g., tremors, stiff gait). But non-motor symptoms might be things like loss of sense of smell, decline in ability to multi-task, REM sleep disorder. These are not unique to PD and again, no objective measures are available. (I had all these symptoms, by the way, but never in my wildest dreams would I have associated these with Parkinson’s.)
So what does this mean for PD research?
–The dilemma that non-motor symptoms appear way before motor symptoms, but motor symptoms are what drive diagnosis means that potential treatments are not being tested early enough in the disease progression.
–The inaccuracy of diagnosis, even when it’s based on motor symptoms and even when made by experts, means research can be “underpowered” because not everyone in the PD treatment group may actually have PD! This makes the low number of participants in clinical trials effectively even lower.
How does a clinician diagnose Parkinson’s? See my next post.