Well, a friend of mine with long-standing PD, was insisting that anhedonia in PD was unique and not 'just' a symptom of depression. Coming from a background and training and experience in psychiatry (and I'm looking at YOU @A MyParkinsonsTeam Member as well !), I was initially dismissive, since I assumed that it was an alternate manifestation of one of the core symptoms of depression: for some people, rather than feeling 'sadness' they feel a loss of pleasure around things that used to give them pleasure. I first thought that all the talk of anhedonia was really talk about depression in PD.
I've since discovered that there's a growing body of professional literature on anhedonia in PD. Somewhere around 30-40% of people with PD also have depression. But dopamine, the chemical which we have a shortage of, is key to the proper functioning of the brain's reward system. The shortage of dopamine can affect our ability to anticipate reward/pleasure and lead to apathy. It doesn't seem that high rates of depression fully explain the high frequencies of anhedonia in people with PD. Interestingly, some studies suggest that people who start with left-sided tremor (that's me!) are particularly at risk for anhedonia and also that anhedonia might even precede appearance of motor symptoms by several years.
So, yes, anhedonia can certainly be part of depression, and people with PD are at very high risk of depression. But it does appear that some anhedonia in PD isn't part of depression. In any case, those of us with PD are particularly at risk of anhedonia/apathy, with or without having major depressive disorder.
I think that clinical and basic research scientists are still trying to disentangle the relationship between depression, anhedonia and PD. Let's say that it's complicated.

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A MyParki...

ANHEDONIA: For years I suffered from Anhedonia but did not know what is was. I thought we all felt this way. I went without treatment until I finally realized something was wrong. A simple example of this disease is that I did not want a candy bar because I would just eat it up and then it would be gone so what was the use of having the pleasure of eating a candy bar? I know it was crazy but that was how I felt about everything. It was a lesson in futility. I still will slip into a slight phase of Anhedonia now that I have PD. And having PD sometimes feels futile because there is no cure. But our Father in Heaven holds my hand and leads me back to the reality of this life I have. And with HIM, all things are possible and out of such a stark reality I am uplifted. Sterling

Dopamine agonists (like Mirapex) are known to cause compulsive behavior. My 92 year old dad became hypersexual when they increased his dosage to a very high level. (His nursing home staff were frantic and didn't know what to do!!) All we had to ask the doc to do was to decrease Mirapex down to its previous level. He was then fine. So, @A MyParkinsonsTeam Member , an adjustment of dosage may be in order. You may be able to tolerate a lower dose. All I know is that my movement disorders doc won't let me near it, given my family history of bipolar disorder. Meanwhile, my dad --who never had bipolar disorder himself-- reacted to the medication. His mom and sister had BPD and that puts one at risk of reacting to dopamine agonists by displaying this kind of behavior. @A MyParkinsonsTeam Member, what you are saying makes perfect sense, in that it produces a manic-like state with compulsive behaviors in some people, especially those with that propensity/vulnerability.

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A MyParki...

@A MyParkinsonsTeam Member, I understand your nervousness and frustration. But the fact is that different people respond differently to different meds. So there are med guidelines, but people also come with their own constitutions/sensitivities that make them react differently to the exact same meds. That's why they always say that medicine is as much art as science. It's frustrating, but there's no way around it. And since many of with PD have other medical conditions that complicate administration of any 'standard' treatment, there can never be a standard treatment protocol.
Plus, there are many different genetic propensities and environmental exposures that probably lead to PD. (They've identified at least a half dozen genetic variants.)That's why there is unlikely to be A 'cure for PD' or A 'cure for cancer." The former are a group of conditions that lead to a depletion of dopamine-generating cells in the brain, but I like the words of one wise PD doc who said, "If you've seen one person with Parkinson's disease, you've seen one person with Parkinson's disease." Our dosing, clinical course, side effects and responses to medications are likely to vary from person to person. That's why research talks more about complex diseases like PD in terms of 'risk factors' rather than 'causes'.There are multiple roads to PD,so there are multiple treatment options to consider.
But I don't really think it's terribly different for most disorders. Disorders with simple causes and simple treatments are the exception.An antibiotic for PD? Would be nice if it were that simple. Well, some have proposed viral or bacterial causes, or factors in the gastric microbiome. These are likely to be contributory (risk factors) rather than simply causal, if they are found to have any role at all.

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A MyParki...

@ Sterling1, I believe , the so called anhedonia- the inabilty to feel pleasure is a misnomer, I think a better term is apathy which is not caring for the things one liked before having PD.. In any case I think either way one wants it called both anhedonia and apathy should be treated. God Bless.