Actress Sarah Chalke's son Charlie has been diagnosed with rare autoimmune disorder Kawasaki Disease (Kd).

The former Scrubs star shot a guest appearance on U.S. medical series Grey's Anatomy in late 2012, and she now reveals the episode was inspired by her own three year old's struggle with the disease, which causes the body's blood vessels to become inflamed.

Desperate to shine a light on the condition, Chalke approached series creator Shonda Rhimes about an idea for a storyline, and the 36 year old, who also plays a mum on the show, admits she was shocked when producers cast a young boy with Kd as her child.

She tells The Hollywood Reporter, "Something pretty crazy happened the moment I started shooting; I got an email from my Kawasaki doctor and she received an email from a patient's mother who had cast a triplet to play my son - it was a four-year-old and one of them had Kd a year ago. It was a complete coincidence."

And Chalke hopes the episode will help other parents in similar situations: "What I loved about this story was it tells a very common Kd experience, so that a parent might be able to relate to it or see the symptoms. After experiencing it, there's a message to parents: fight for your kid, don't be scared to get a second, third, sixth opinion or go into an Er (Emergency Room) and put your foot down."

The actress is just glad to have turned her difficult ordeal into something positive: "When you go through something, it's not what happens to you in your life, it's how you deal with it. It was such a traumatic, hard thing and we had to pull something good out of this; there had to be a reason why this happened."