ET is calmed by a drink or two of alcohol, PD tremor is unaffected by alcohol.
A resting tremor can be seen by laying both hands in the lap, with the arms completely relaxed. In my early years, I could stop the tremor by relaxing very completely, but it returned within a few seconds, depending on how medicated I was. Now, on Sinemet and a dopamine agonist and Amantadine and Cymbalta), I almost never see it except under stress (like watching the battle at Minas Tirith in
The Lord of the Rings).
I have known several very early onset people who said they started with ET and then it became PD tremor after a few years.
There are hundreds of disorders that tremor is a symptom of. Just because someone shakes or taps or quivers doesn't mean they have PD
or ET.
Doctors have told me that tremor is the most intractable symptom of PD, an they don't know what causes it or how it works--unless someone has found out in the last six months, the recent speed of basic science discoveries being what it is.
Yes, I have read somewhere that cerebellar ataxia and PD can be mistaken for each other, and there seem to be different varieties of ataxias, just as there are apparently many forms of PD. It's amazing anyone gets diagnosed at all, considering that we still don't know the basic science of what causes or perpetuates PD. They have to have theories/hypotheses to test, and then the results have to be replicated by other researchers doing the same experiment, yadda yadda, but that's how we get scientific results and not just stories. Stories are valuable, but don't generally lead to a rigorous line of reasoning.
Spect scans have been considered unreliable for many PWPs and are very expensive. I don't have time to check this out, but maybe someone else knows more of the facts or conjectures.
Personally, I think that everyone who shakes should have their vitamin D3 level checked. Without heavy supplementation (or what used to be considered heavy), my legs shake and internal tremors curl me up until I can't walk, sometimes not even with a cane. I am careful to follow doctors orders on dosage, because too much can be as bad as too little. I can always ask for another blood level test if I don't think I'm getting enough.
Oh yes, almost forgot, I read somewhere that a PD tremor is usually about 5-7 Hz (cycles per second). Don't know how generally true or false that may be.
Now you know the entire contents of the top of my head, and I have to sleep to get it refilled.
Best of luck,
Jaye