Parkinson's and concussion relationship

In 2011 I was involved in a car accident - the back of my head had three large bumps (concussion) and my SI joint was fractured. Three surgeries later I continue to walk. But in 2018 I was diagnosed with Young Onset Parkinson's-my tremors are controlled with med's, however 'some doc's' are stating I may have been misdiagosed. At 57 years young-doc's are concerned with my cognitive impairment I have been experiencing. These doc's have no answers, no other diagnosis-just 'we really don't know what is causing the rapid cognitive decline'. I am trying to find a doctor who has studied, or have had patients with simialar scenarios. Anyone have any info on the link between Concussion/Parkinson's/Cognitive Impairment?