Robin Williams' suicide could have been triggered by a common but devastating form of dementia that may have disrupted his normal brain function.

Court documents obtained by TMZ reveal that Williams, who was found hanging from a belt at his home in California last August, was suffering from dementia with Lewy bodies.

Sources connected with the troubled comic's family told the news site that the degenerative disease was the 'key factor' they believe drove him to take his own life.

Robin Williams was found hanging from a belt at his home in California last August. It has emerged that the actor was was suffering from dementia with Lewy bodies

Hallucinations and delusions are common among those affected by Lewy bodies dementia, and sufferers often struggle to identify friends and family. The disease also typically causes problems with attention and alertness.

'The condition itself is caused by the build-up of protein into clumps, called Lewy bodies, in the brain, which can damage nerve cells in areas involved in memory and thinking,' explained Hilary Evans, Director of External Affairs at Alzheimer’s Research UK.

'These protein clumps also play a role in Parkinson's disease, so some people with dementia with Lewy bodies will also experience movement symptoms similar to those seen in Parkinson's.'

On Friday, authorities formally ruled the star's death as suicide as it was revealed he was struggling with a recent diagnosis of Parkinson's Disease as well as anxiety, depression and paranoia.

It was found that the Mrs Doubtfire star - who had battled drink and drugs in the past - had four drugs in his system at the time of his death. Toxicology reports found two anti-depressants and two caffeine compounds and there was no alcohol in his system.

When authorities found Robin's body, the reports states they saw a closed bottle of Seroquel, a drug that treats schizophrenia, bipolar disorders and depression. It was prescribed a week before he died.

Robin Williams with his third wife Susan Schneider. Sources connected with the troubled comic's family told TMZ that the degenerative disease was the 'key factor' they believe drove him to take his own life

The legendary comic battled paranoia, according to the report, and the night before he died, he placed several wristwatches in a sock and gave them to someone because he was worried about their safe keeping.

The report says the last outgoing call from Robin's phone was at 7.08 PM the night before he died. He had called his wife Susan, and it lasted 38 seconds.

Susan told authorities he called because he was picking up magazines for her at a bookstore.

When asked about his behavior, Susan said he seemed well and had taken his iPad from their closet which she took to be a good sign because he hadn't watched TV or read anything in about six months.

WHAT IS LEWY BODIES DEMENTIA? LBD is a common form of dementia - it affects an estimated 1.3 million people in the United States. The disease is caused by abnormal microscopic deposits that damage brain cells over time This leads to a decline in thinking, reasoning and independent function The disease takes its name from Frederick H. Lewy - the neurologist who discovered the brain abnormalities during the early 1900s It shares symptoms with Parkinson's Disease - sufferers can experience motor control problems, such as hunched posture, rigid muscles and a shuffling walk Those affected can suffer visual hallucinations, which generally take the form of phantom objects, people or animals there It is also linked to Alzheimer's disease as it is more common over the age of 65 and those affected often suffer from confusion and memory loss Advertisement

The web browser had several tabs open to websites discussing medications, including Lyrica, an anti-seizure drug, and propranolol, which treats blood pressure and tremors.

The couple were sleeping in separate bedrooms, Susan said, because Robin was having trouble sleeping and would talk loudly in his sleep.

The last time she saw him was around 10.30pm on Sunday night and said he seemed 'excited'.

According to the report, Robin had experienced Parkinson's symptoms since 2011. He had a tremor in his left arm and movement in his left hand had slowed.

He had recently started taking Levodopa to treat the symptoms.

Known as 'the funniest man alive', Williams fought drug and alcohol problems when he played a lead role in the Mork & Mindy sitcom, on his path to stardom.

He had stayed mainly sober for 20 years but in July he went into rehab to use the 12-step program he championed, this time during a brief stay at a Minnesota facility.

Publicist Mara Buxbaum said at the time that Williams had not fallen off the wagon, but was 'taking the opportunity to fine-tune and focus on his continued commitment, of which he remains extremely proud.'

This year he has six movies either out or due for release and had also been working on the TV series The Crazy Ones - but it was axed after one season.

He admitted he returned to TV after nearly three decades because two divorces have left him short of cash.