The Oscar winner battled the condition, often caused by the removal of lymph nodes during cancer treatment, following her 2012 double mastectomy.
She has since used her experience to help others, filming a PSA for the Center for Disease Control to steer other sufferers in the right direction for help.
"In my case the lymph fluid built up in my arms," Bates tells ABC News. "I had seen my mother go through this but I didn't know what it was. I went to a doctor who helped me with manual lymph drainage in my arms and I had to go several times a week. It's called lymphedema and 10 million Americans suffer from it. Your legs and arms just swell up."
But doctors are ill-equipped to diagnose the condition, which means so many people get the wrong treatment.
"Doctors spend an entire 15 minutes in medical school on the lymphatic system," the "Misery" star explains. "If you go to your general practitioner and you have a problem, he'll say, 'Go home and eat salads'. Unfortunately it's progressive and incurable and many people can't afford to doctor shop so they go for years without getting help."
But her video for the CDC is helping people - like Rockwell's mum. "I met Sam Rockwell's uncle, and his mom had a swollen arm and didn't know what it was. She saw one of the programmes that I've been able to do and she got to a doctor and got treatment and she's better," Kathy beams.