Loss of smell is an early indication that PD is on the horizon. I lost my sense of smell in the mid 1970's. It was blamed on a bad virus that I had. Since then it has been documented as an early warning for PD. I had no PD symptoms until late 2007. November 2007 I had a cloectomy/ileostomy. That's where your colon is removed and you wear a bag to catch your poop. The surgery went bad and a week later I had peritonitis. That's where digestive fluid leaks into your abdomen. I almost did not make it. A couple months later I noticed that I did not walk as usual and I had lost some coordination in my right hand. I blamed it on a small stroke from the peritonitis. Within a year I developed tremors in my right hand and a blank look on my face. I was diagnosed with PD.
My thought is that the peritonitis triggered the start of PD.