A pathology report obtained by FOX 411 revealed that prior to his death, Robin Williams was suffering from diffuse Lewy Body dementia (LBD) in addition to Parkinson’s disease, which he was diagnosed with in Nov. 2013.

“It is important to note that patients with diffuse Lewy Body dementia frequently present with Parkinsonian motor symptoms and … depression and hallucinations,” explains a pathology report obtained by FOX411.

According to the Lewy Body Dementia Association (LBDA), the disease affects an estimated 1.3 individuals in the United States. Onset typically occurs between the ages of 50 and 85. LBD is an umbrella term for two related clinical diagnoses: Dementia with Lewy bodies and Parkinson’s disease dementia.

Dementia with Lewy bodies is a type of progressive dementia that leads to a decline in thinking, reasoning and independent function, due to abnormal microscopic deposits that cause brain cell damage over time, according to the Alzheimer’s Association.

Parkinson’s disease dementia is an impairment in thinking and reasoning that eventually affects many people with Parkinson’s, according to the Alzheimer’s Association.

The two diseases are characterized by different early symptoms, but they reflect the same underlying biological changes in the brain, and, over time, patients with both diagnoses will develop very similar cognitive, physical, sleep, and behavioral symptoms, according to LBDA.

Patients with LBD show different degrees of symptoms, which may fluctuate as often as moment-to-moment, hour-to-hour or day-to-day, LBDA notes on its website.

Symptoms can include: progressive dementia, recurrent complex visual hallucinations that are typically well-formed and detailed, REM sleep behavior disorder, and fluctuating cognition with pronounced variations in attention and alertness.

LBD is diagnosed clinically through physical and neurological examinations, patient and family interviews, and neuro-psychological and mental status tests. However, a postmortem autopsy is the only way to obtain a conclusive diagnosis of LBD.

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According to LBDA, medication treatment is one of the most controversial subjects in dealing with LBD, as medication that works for one person may not work for another. Williams’ pathology report revealed that he had been taking pramipexole and levodopa, drugs prescribed to manage symptoms of Parkinson’s. Both drugs list hallucinations as a side effect.

There is no cure of definitive treatment for LBD, and the disease has an average duration of 5 to 7 years. However, the disease could span from to 20 years, depending on factors such as overall health and severity of symptoms, LBDA noted.

TMZ reported that friends and family of Williams believe Lewy Body dementia was the main factor that led to his sudden suicide in August.

In addition to the Parkinson’s and dementia, Williams had a history of depression, paranoia, compulsiveness and anxiety.