What is the difference between 'internal tremor' and 'external tremor'?

What is the difference between 'internal tremor' and 'external tremor'?

Neal Hermanowicz (Director of the Movement Disorders Program) gives expert video advice on: How is dexterity affected by Parkinson's?; How does Parksinson's affect the skin?; How does Parkinson's affect body weight? and more...

Internal tremor is what people feel, but we can't as a clinician see it. People will say, I feel as if I am shaking inside myself, but it is not visible to the patient nor to the clinician. I suspect that's simply a subtle tremor that's not visibly detectible either by the clinician or by the patient. It's a manifestation of the same process. It's just not obvious.