'20/20' FEATURES ONE MAN'S INSPIRATIONAL JOURNEY AS HE RECEIVES A RARE HAND TRANSPLANT AFTER GOING FROM FITNESS FANATIC TO DEATH'S DOOR OVERNIGHT

Hour Includes Video Diaries Documenting Dramatic Decline in Health and Miraculous Recovery in Real Time

'20/20' Airs on the West Coast, Friday, April 19 (10:00 - 11:00 p.m. PDT), on ABC

On "20/20," ABC News' Juju Chang reports on the inspirational journey of a reality television executive who fought back from death's door and lived to tell the tale, featuring video diaries in real time of his mysterious, rapid decline in health and miraculous recovery. "20/20" airs only on the West Coast, Friday, April 19 (10:00-11:00 p.m. PDT), on ABC. (Rebroadcast. ABC OAD: 8/25/17)

Jonathan Koch was the poster child of "clean living" - never smoking nor drinking alcohol or coffee and exercising regularly. As the co-founder of the production company Asylum Entertainment, he was traveling to a conference when he started to feel sick. Overnight, Koch went from fitness fanatic to intensive care hospital patient when his organs began to suddenly fail.

Doctors were baffled about what was killing him and why the treatment they were giving him was ineffective. They put Koch in what was essentially a medically induced coma, but soon gangrene set in and his limbs began to die. Two days later, doctors determined that he had an uncommon and aggressive autoimmune disease called hemophagocytic lymphohistiocytosis (HLH). Once on chemotherapy and steroids, he began to recover; but there was irreversible damage to his extremities causing him unspeakable pain. Eventually, his left hand and the fingers on his right hand, his right leg and the toes on his left foot were amputated. Unable to use his hands and legs Koch relied heavily on his then-fianc�e, now wife, Jennifer Gunkel.

Dr. Kodi Azari, one of the world's leading hand transplant pioneers, gave him new hope of a better functioning life. Koch was in poor health and spent weeks in rigorous physical therapy pushing himself to get into shape and become eligible for a rare hand transplant that is one of the first of its kind. Finally, a donor hand became available; and 21 months after he almost lost his life, Koch woke up with a new hand. Determined, Koch continued his physical therapy making progress at an unprecedented rate, even surprising Dr. Azari, and last summer Koch met his donor's family.

The report includes interviews with Koch; Gunkel, who recorded the video diaries; Dr. Azari; Dr. Lynn Abell and Dr. Michael Seneff, heads of the team who first diagnosed Koch; Lisa Koch, Koch's sister; Jewel, singer and Koch's friend; retired captain Chesley "Sully" Sullenberger, whose story inspired Dr. Azari's preparation for the groundbreaking surgery; Joel Surnow, creator of "24" and Koch's friend.

"20/20" is anchored by David Muir and Amy Robach. David Sloan is senior executive producer.