In our experience, process of elimination. It took many years to find a doctor familiar with PSP and that seems to be the experience of many. My mother had so many tests and was thought to have a stroke, nueropathy, Myesthenia Gravis, etc. She had a low blood pressure event that caused her to loose consciousness and was taken to the ER. The Neurologist on call there diagnosed her with PSP. I have heard of others who were initially diagnosed with Parkinsons, but when the medications have no effect, then PSP might be diagnosed.