Depression Did Not Kill Robin Williams-Wife!

When Robin Williams took his life in 2014, he left his millions of fans, family, and friends shocked and grieving – no one more so than his widow Susan Williams, who for the last year has remained mostly silent about her husband's tragic passing in an effort to uncover and study the real cause of his death. Watch video below

Now in one of her first interviews since losing Williams' last August, Susan shares with PEOPLE the details of the debilitating brain disease called Diffuse Lewy Body Dementia or Dementia with Lewy bodies (DLB) that took hold of Williams and the couple's harrowing ordeal to fight it.

"It was not depression that killed Robin," Susan says, speaking to the public perception of what drove Williams to commit suicide. "Depression was one of let's call it 50 symptoms and it was a small one."

Frequently misdiagnosed, DLB is the second most common neurodegenerative dementia after Alzheimer's and causes fluctuations in mental status, hallucinations and impairment of motor function. The disease started taking its toll on Williams in the last year before his death, by way of its "whack-a-mole"-like symptoms which included heightened levels of anxiety, delusions and impaired movement.

"They present themselves like a pinball machine," Susan says. "You don't know exactly what you're looking at."

Williams' symptoms worsened in the months leading up to his death. He experienced crippling anxiety attacks, a "miscalculation" with a door that left his head bloodied and muscle rigidity. And yet still his team of doctors could not pinpoint exactly what was wrong – until the autopsy.

"I know now the doctors, the whole team was doing exactly the right things," Susan says. "It's just that this disease was faster than us and bigger than us. We would have gotten there eventually."

Susan hopes that she can use what she's learned to help others afflicted by DLB.

"I've spent this last year trying to find out what killed Robin. To understand what we were fighting, what we were in the trenches fighting and one of the doctors said, 'Robin was very aware that he was losing his mind and there was nothing he could do about it,' " she says.

"This was a very unique case and I pray to God that it will shed some light on Lewy bodies for the millions of people and their loved ones who are suffering with it," adds Susan. "Because we didn't know. He didn't know."people