Liz Feldman said that they had filmed half of the final season of the Netflix series by the time the actress, 50, discovered she had the condition.
WATCH: Official trailer for Dead to Me season two on Netflix
The producer revealed that the star, who plays the character Jen, opted to finish making the series, but that there were some changes that had to be made. Speaking to Buzzfeed, she said: “We had already shot 50 per cent of the final season by the time she received her diagnosis.
“On Dead to Me, we shoot completely out of order. We had shot scenes from all 10 episodes by the time the news came in, and there was no going back. We were stuck with the story that we had to tell, but also, that's the story Christina wanted to tell. She chose to finish.
“We did it on her terms, and nothing in the script changed, really, at all. We did whatever we needed to do to accommodate her in terms of blocking.” MS - which affects 2.1 million people worldwide - can cause fatigue and pain, as well as problems with vision, mobility and thinking.
The show, which also stars James Marsden, recently arrived for a new third season on the streaming platform. It tells the story of Jen and Judy (played by Linda Cardellini) who form a friendship in very unlikely circumstances.
Christina Applegate stars alongside Linda Cardellini in Dead To Me
Speaking earlier this month to the New York Times about whether there were discussions about stopping production, Christina explained why she wanted to continue. The star - who recently received a star on the Hollywood Walk of Fame - said: “I had an obligation to Liz and to Linda, to our story.”
Like this story? Sign up to our What to Watch newsletter and get the heads-up on the shows and films everyone’s talking about.