My understanding is that essential tremor is not part of Parkinson's but anyone can have both at the same time. Essential tremor is often mistaken (misshaken? Ha!) for Parkinson's and quite often self diagnosed which can be problematic. The shake is usually manifested in a slightly different way however.

I was once told essential tremor can be caused from some medications. check the side effects on what you take.

When I was duagnosed it was Parkinson's on the left side and a year lady I was told the shaking in my right arm was a familial essential tremor and both are independent of each other ...I can tell you when I have too much caffeine the essential Tremor goes wild but I can usually make it stop if I concentrate whereas the parkinsons which is now bilateral I can't think it or concentrate it to stop only carbidopa/levedopa works

I had essential tremor in both hands for many years. Then the left go worse about six months ago and six weeks ago I was diagnose with Essential Tremor + Parkinson's.

Thanks for the input TimBall..