Lewis, 77, was diagnosed with idiopathic pulmonary fibrosis two years ago. There is no known cause or cure for IPF, but the steroids that Lewis has taken to help fight the condition have caused him to gain more than 50 pounds.
Pulmonary fibrosis interferes with the ability to transfer oxygen from the lungs to the bloodstream, as the lung's air sacs, called alveoli, are gradually replaced by scar tissue. Over time, breathing becomes more difficult, and likely outcomes include either respiratory or heart failure.
In Los Angeles, MDA spokesman Bob Mackle told United Press International Lewis is "doing OK," although he is struggling.
"It tires him," said Mackle. "He put a full day in the office (Monday). He'll be here all week. He's trying to do as much work as he can to prepare for the show. At the same time, he's trying to get enough rest so he can do as many hours as he can."
The annual Labor Day telethon is scheduled to air on close to 200 TV stations, beginning at 9 p.m. EDT Sunday, and signing off at 6:30 p.m. EDT on Monday. Mackle said Lewis expects to appear on camera for the first few hours of the telethon, then take a break and return for the final hours Monday afternoon.
"He wants to do at least as many hours as he did last year," said Mackle.
Ed McMahon will carry much of the load in his familiar role as the show's anchor. Co-hosts for the 21 1/2-hour telethon include Jann Carl ("Entertainment Tonight"), comedian Norm Crosby and singer Billy Gilman.
This year's lineup of stars performing or appearing on the telethon includes Celine Dion, Cher and Billy Crystal. The show will also feature Clay Aiken ("American Idol"), comedian Steve Harvey, Al Jarreau, Joan Jett & the Blackhearts, Charo and comedian Don Rickles.
Mackle, who has been with the MDA for 12 years, said organizers are staying loose, ready to add more talent if the opportunity arises between now and Sunday. He said it is not uncommon for a major artist to "suddenly become available" at the last minute -- and telethon producers are more than willing to find them a slot on the show.
"We have enough flexibility in a 21 1/2-hour show if somebody really big comes up," he said. "You never know, every year we have something that pops up at the last minute. They come out of the blue."
That kind of flexibility can also pose huge headaches for producers and backstage crew.
"Things change minute to minute," said Mackle. "We have talent who for one reason or another -- illness, maybe -- drop out. You can imagine the complexities of putting on a sitcom or an hourlong drama -- imagine trying to do it for 21 hours straight. The logistics are incredible."
New technology has helped in one of the more challenging aspects of producing a nationwide telethon -- communicating with local stations as last-minute programming decisions force changes in the planned schedule. Mackle said the Internet has made it possible for telethon producers to communicate with local stations more or less on a real time basis.
Mackle said changing times have also prompted telethon organizers to adjust their vocabulary -- "things that were politically correct before, aren't now" -- but he said some basic elements of the telethon have changed little from its earlier days.
"Kids and adults still show up at stations and dump the money they have raised in a fishbowl," he said. "With all the high-tech fundraising techniques, it's still a lot of people going to their neighbors for help, and firefighters standing on the corner -- things like that. That's where most of our money comes from."
Mackle said the MDA has traditionally chosen not to apply for government funding grants, in the interest of avoiding "the red tape and the bureaucracy." He said the group has lobbied in recent years to have the government give more money directly to researchers.
As Lewis continues to experience health problems, and as he approaches his 80th birthday, the question inevitably arises: How long can he go on with the telethon? Mackle said Lewis actually never talks about that.
"No, all he talks about is pushing hard to find treatments and cures while he is still here," said Mackle. "I don't think there's been any discussion of stopping even if Jerry wasn't here to carry on. I dont think he would want it to stop."
Does Lewis, afer all these years, have a sense of his legacy -- as a prime benefactor of research into muscular dystrophy?
"I think he's proud of what he does," said Mackle. "I've never actually heard him refer to it in terms of history or legacy. Other people have, and he just brushes it off. He's been doing it for 50 years, so it's just part of his life."