It depends on your symptoms. My husband's symptoms were really obvious, once we started to pay attention. When I described his symptoms to the neurologist, she immediately said, "Yes, he has Parkinson's." In his case, he was much slower, had resting tremors, walked hunched over and shuffled, and had stiff arm movements, as well as soft speech and tiny writing. If you have non-motor symptoms, it can be harder. They can test for dopamine in your brain with a DaT scan, but that doesn't differentiate between Parkinson's and the other Parkinsonisms. Often the doctor will prescribe carbidopa and if you respond well to that, by reduced tremors and better balance, that is all the confirmation they need.

The DATSCAN is the only definitive answer. All the test etc. are just a waste of time. Good luck.

DatScan is a definite answer.

another test that the neurologists sometimes use is the pull test
"Postural reflexes are impaired in conditions such as Parkinson's disease, leading to difficulty walking and falls. In clinical practice, postural responses are assessed using the “pull test,” where an examiner tugs the prewarned standing patient backward at the shoulders and grades the response"

DATSCAN is the definitive test.