PHILADELPHIA (CBS) – It’s a mysterious brain illness that triggers psychotic and violent behavior.

It is rare, and it is often misdiagnosed.

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One desperate family grabbed a video camera to document what was happening.

In the tape, seven-year-old Paul Michael Nelson can be seen yelling uncontrollably while being restrained.

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He started to experience the episodes in 2009.

“In the night, he was tearing up the flooring, he took a knife to the office door,” recalls his mother, Mary Nelson.

His family started recording the outbursts because some doctors didn’t believe them.

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“He was flopping around on his knees barking like a dog,” Paul Michael’s mother says.

Over five years, Paul Michael was hospitalized 50 times and even occasionally removed from his home by police.

No one could figure out what was wrong.

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“All of a sudden, our kid goes from, he’s an angel in the Christmas play, looking cute as could be, to what you just saw,” Mary explains.

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A blood test finally revealed PANS – Pediatric Acute-onset Neuropsychiatric Syndrome. It’s marked by sudden and dramatic outbursts and obsessive behavior, and it’s unusual.

We discovered that he actually had an autoimmune disease attacking his blood and blood vessels,” explains Dr. Jennifer Frankovitch.

It was also attacking the brain, triggering psychiatric problems.

A lot isn’t known about the newly identified syndrome.

“Maybe about 14 to 40 percent of the cases, we think strep triggers it…we just don’t know yet,” Dr. Frankovitch says.

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Paul Michael, who has one of the more severe cases, is 12 now and doing much better with treatment that can include antibiotics.

Doctors say that while strep is infectious, PANS is not. It’s not known how or why some infections trigger the syndrome.

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Stephanie Stahl