It has been reported that some patients have been misdiagnosed with Essential Tremor, when in fact the correct diagnosis in their specific case was Parkinson's Disease.
Parkinsons disease should be diagnosed by a neurologist. There is no single test used to confirm diagnosis. The diagnosis is based on a physical test, review of medical history, and a neurological examination. Lab tests may be required to rule out other dieases. The condition can not be cured but there are medications available to control the symptoms with high success.