In his years of caring for patients with Parkinson's disease, Dr. Bastiaan R. Bloem thought he had seen it all. But the 58-year-old man who came to see him recently was a total surprise.

He had had Parkinson's disease for 10 years, and it had progressed until he was severely affected, unable to walk. He could walk only a few steps before falling, but the man told Dr. Bloem something amazing: he said he was a daily cyclist.

"I said, ‘This cannot be. This man has end-stage Parkinson's disease."

(READ More in the New York Times)