DEARBORN, Mich. -

When you hear the word "arthritis," what do you picture? An elderly grandparent? An aging athlete with a bum knee? How about a five-year-old boy?

Zach Fradkin of Dearborn, Mich., is one of 300,000 children in the U.S. suffering from arthritis. He was diagnosed when he was just a toddler, after suffering a seemingly innocent fall that left him limping.

At first, his pediatrician wasn't concerned, but over the next three weeks, Zach got progressively worse.

"He went from walking to crawling to just dragging himself around on the floor on his hands," said Andy Fradkin, Zach's dad. "That progression of pain was really intense and really quick."

What happened next stunned Zach's parents.

"The pediatrician said, 'I think he has arthritis,'" said Andy. "The thought running through my mind was, 'Arthritis? He's 18 months.'"

A blood test confirmed it.

"It was a shock," said Amy Fradkin, Zach's mom.

"Juvenile idiopathic arthritis is an autoimmune disease which means that basically your immune system goes haywire and starts attacking your joints. We call it 'idiopathic' because we don't actually know exactly what causes it," said Dr. Meredith Riebschleger, a pediatric rheumatologist at the University of Michigan.

Although arthritis is often associated with the elderly, several forms of arthritis are common in children and younger adults. According to the Arthritis Foundation, 65 percent of the people with arthritis are under the age of 65.

Zach's case is unusual in that he had so much pain, he was diagnosed quickly. Many children go undiagnosed for years.

"The thing that will often bring them to our attention is if someone notices that they have a limp. Suddenly, they're having trouble opening up jars or their writing gets more messy," said Riebschleger. "You'll notice some swelling of the joints, some redness, but you're not going to see it unless you're looking for it."

Zach developed arthritis in his ankles, knees, and fingers. Arthritis isn't Zach's only challenge, as he's also on the autism spectrum and non-verbal. This made managing his arthritis more difficult.

For years, even an ordinary illness would aggravate his symptoms.

"An ear infection would give him a flare-up and he couldn't stand," said Amy. "Instead of getting a fever, he couldn't stand or walk."

The most difficult part for the Fradkins -- seeing their child in pain.

"Severe pain. He would curl up in a little ball and just cry," said Andy. "You just wanted to do something for him, but you just couldn't."

Zach is currently taking a low-dose chemotherapy drug, two anti-inflammatory medicines, and ten additional medications to counter the side effects of the other drugs. He's also on a gluten-free and dairy-free diet.

Zach's arthritis is finally under control, but it's been a long journey.

"When one treatment didn't work, it lead to more treatment, and more drugs, and more drugs to counteract those drugs and more tests and more blood tests," said Andy.

Zach's regimen of medications isn't unusual.

"We have great drugs to treat arthritis now, we really do," said Riebschleger, "but they all carry with them side effects and unfortunately, we often need a combination to get control of the disease."

There's also long-term worries. Children with arthritis can suffer from abnormal bone growth, need joint replacement surgeries or have other serious complications.

The Fradkins hope to help change that.

"There really isn't the amount of research into it that some other diseases have," said Andy.