The 56-year-old Oscar winner, who was diagnosed with the painful disease at age 50, took to Instagram on Wednesday to share a photo of her back, which was covered with multiple bruises and surgery scars.
"Living with rheumatoid arthritis," O'Neal wrote in her caption. She went on to detail the origin of each of her scars.
"A fall scratch scar on my right hip. And the back surgery scar from eight years ago. My last back surgery scar is on the front from February. And all those red marks are from heating pads. I probably should turn those down a little bit, " she wrote.
"Believe it or not this is me actually getting better," the actress revealed. "Cheers to everyone and rheumatoid arthritis can go f--- itself."
She added the hashtag #rheumatoidarthritiswarrior.
Just days before, O'Neal shared another photo of herself sitting on a couch alongside her dog to let friends and fans know she was "on the mend" after dealing with "rheumatoid arthritis bull crap."
"I hate texting," she added, "because my hands suck Right now ... so If I don’t text you back I promise it’s nothing personal."
Rheumatoid arthritis, or RA, is an autoimmune disease that occurs when the immune system mistakenly attacks the joints, causing inflammation, joint pain and swelling, the American College of Rheumatology explains.
The often debilitating disease affects more than 1.3 million Americans, with about three-quarters of the patients women, and can start at any age, but it most often begins between 30 and 50.