Late comedian and actor Robin Williams was suffering from a form of dementia at the time of his passing, a pathology report revealed Tuesday.
Williams committed suicide on August 11, and sources report that the Lewy Body Dementia (LBD) diagnosis was the "key factor" in his death.
LBD can cause visual hallucinations, rigid muscles, and tremors. The progressive disease slowly erodes a sufferer's mental abilities, and can resemble Alzheimer's and Parkinson's disease in its symptoms. Williams was diagnosed with Parkinson's disease in November 2013.
"It is important to note that patients with diffuse Lewy Body dementia frequently present with Parkinsonian motor symptoms and ... depression and hallucinations," Williams' pathology report read.
The report's finding of LBD means that there were abnormal protein deposits, or Lewy bodies, spread throughout Williams' brain. Treatment for the incurable disease is "challenging," according to the Mayo Clinic, and Williams' wife reportedly told police that he was complaining about the way the medication made him feel.
The pathology report revealed that Williams was taking pramipexole and levodopa, drugs used to manage Parkinson's symptoms, at the time of his passing. Hallucination is a potential side effect of both medications.
Lewy Body Dementia Association (LBDA) Scientific Advisory Council member Dr. Dennis Dickson explained some of the symptoms that Williams was suffering before his death.
"Mr. Williams was given a clinical diagnosis of PD and treated for motor symptoms," Dickson said.
"The report confirms he experienced depression, anxiety and paranoia, which may occur in either Parkinson's disease or dementia with Lewy bodies."
According to the LBDA, an estimated 1.3 million people in the United States suffer from LBD, and it may take more than two years for a doctor to diagnose the disease based on presented symptoms.