A few months later, a medical examiner's report found Williams, 63, had been suffering from Lewy body dementia, a disorder characterized by rapid cognitive decline caused by protein deposits on the brain's neurons. It shares symptoms with Alzheimer's and Parkinson's — in fact, LBD is often misdiagnosed as Parkinson's, as it was in his case.
For many fans, it was likely the first time they'd ever heard of LBD, a rare disorder that strikes some 1.5 million Americans.
Now, two years after his suicide, his widow, Susan Schneider Williams, has written an essay for the medical journal Neurology that sheds light on the Oscar winner's final month, titled "The terrorist inside my husband's brain."
Williams, who said she did not learn the true cause of his illness until after after his death, revealed that "all four of the doctors I met with afterwards and who had reviewed his records indicated his was one of the worst pathologies they had seen. He had about 40% loss of dopamine neurons and almost no neurons were free of Lewy bodies throughout the entire brain and brainstem."
As early as the fall of 2013, he began displaying what at the time seemed like unrelated symptoms: "constipation, urinary difficulty, heartburn, sleeplessness and insomnia, and a poor sense of smell — and lots of stress."
Williams said that while anxiety was not new for the actor, who had long suffered from depression, the way he now handled it was "markedly out of character for him," to the point of alarming her. "Not until after Robin left us would I discover that a sudden and prolonged spike in fear and anxiety can be an early indication of LBD," she explained.
PHOTOS | Actor, comedian Robin Williams
When he suffered a panic attack and began forgetting his lines on the set of Night at the Museum 3, his doctor prescribed antipsychotic medication, which didn't help. "Not until after he left us would I discover that antipsychotic medications often make things worse for people with LBD," she lamented.
For the first time, my own reasoning had no effect in helping my husband find the light through the tunnels of his fear," Williams realized. "My husband was trapped in the twisted architecture of his neurons and no matter what I did, I could not pull him out."
She likened his arrival home from the Museum set in May 2014 to "a 747 coming in with no landing gear." The Julliard-trained actor was no longer able to hide his illness. "I will never know the true depth of his suffering, nor just how hard he was fighting," she wrote. "But from where I stood, I saw the bravest man in the world playing the hardest role of his life. Robin was losing his mind and he was aware of it."
Later that month came the Parkinson's diagnosis, which she now knows to have been incorrect. But sitting in the doctor's office, she thought, "We had an answer. My heart swelled with hope. But somehow, I knew Robin was not buying it."
Throughout all of the medical testing, she says Williams remained sober, participated in therapy, worked out with his trainer and engaged in his favorite form of exercise, cycling. His ability to ride would eventually be impaired by a growing tremor in his hand and trouble with visual and spatial perception.
Near the end of July, his doctor changed his medications in hopes of keeping the Parkinson's symptoms at bay. On Sunday, Aug. 10, she thought he was getting better.
On his doctor's advice, they had begun sleeping in separate rooms to allow them both more rest. When bedtime came, they each told each other, "Goodnight, my love," and retired to their rooms.
It was the last time she saw him alive. That night, he hanged himself.
"During the final months we shared together, our sights were locked fast on identifying and vanquishing the terrorist within his brain," she wrote. "Since then, I have continued our research but on the other side of that experience, in the realm of the science behind it."
During a review of the medical examiner's report in November 2014, she remembers being asked if she was surprised by their findings. "I said, 'Absolutely not,' even though I had no idea what it meant at the time. The mere fact that something had invaded nearly every region of my husband's brain made perfect sense to me ... The massive proliferation of Lewy bodies throughout his brain had done so much damage to neurons and neurotransmitters that in effect, you could say he had chemical warfare in his brain."
Though in hindsight she believes their medical team was close to discovering what was really happening to Williams before he took his own life, she is doubtful that the correct diagnosis would have made a difference when there was no cure available to him.
"Even if we experienced some level of comfort in knowing the name, and fleeting hope from temporary comfort with medications," she concluded, "the terrorist was still going to kill him."
In the two years since his death, Susan Schneider Williams has formed relationships with doctors from the American Academy of Neurology and joined the board of directors for the American Brain Foundation.
"Hopefully," she told Neurology's readers, "from this sharing of our experience you will be inspired to turn Robin's suffering into something meaningful through your work and wisdom. It is my belief that when healing comes out of Robin's experience, he will not have battled and died in vain."