Dane -- who shot to fame amid six seasons on the hit ABC drama "Grey's Anatomy," where he played Dr. Mark Sloan, affectionately known as "McSteamy" -- said his symptoms began over one year ago, when he began to experience weakness in his right hand.

“My left side is functioning, my right side has completely stopped working,” the Grey’s Anatomy alum said, after sharing he only had “one functioning arm,” in an interview with Diane Sawyer that aired...

"I'll never forget those three letters," he said of the diagnosis.