Kathy Griffin is going public about her mom's battle with dementia. The 58-year-old actress and comedian said in a series of tweets Thursday that it's been "devastating" to watch her mother, Maggie Griffin, rapidly succumb to the condition. "As heartbreaking as this is, I feel the need to share some important info about my mom Maggie," Griffin captioned a photo with her mom. "The pic below, taken in September, was the last time I was able to have a proper\/coherent conversation with her. "Since that photo was taken, she has rapidly fallen into the throes of dementia," she said. "This is never easy for any child, I know this is a reality that millions of people deal with every year. But when it comes to my mom this is particularly hard because her sharp mind was everything." Griffin said it's been heartbreaking to see her mother's "naturally quick, funny and smart" mind slip away over the past two years. Her mom, who is 98 years old, is receiving around-the-clock care. "I want to assure you all that she is not in pain and she is getting the best 24-hour care," Griffin wrote. "In terms of how she is now, at this point she only knows my name and I love you. I know many of you know what that reality is like... I'm still grappling with it." Maggie Griffin starred with her daughter on the Bravo series "Kathy Griffin: My Life on the D-List" and also appeared on her talk show "Kathy." Kathy Griffin often posted photos and videos of her mom and her beloved dog, Twinkle. "Could any photo sum up Maggie more than this one?" Griffin captioned a throwback photo Thursday. "Glass of wine in one hand (from the box, naturally) and her favorite daughter Twinkle in the other." "Star Wars" actor Mark Hamill and YouTube star Shane Dawson were among those to reach out to Griffin online. "We all felt we knew Maggie through your Twitter posts & now we all share your pain as you lose a part of her. Sending her love & warm wishes," Hamill tweeted. "Your mother is one of the most beautiful incredible women to ever grace this planet. i'm so grateful she exists. love u guys so much," Dawson wrote. The World Health Organization reports that about 50 million people worldwide have dementia, with about 10 million new cases each year.