Patrick Stewart battled Lewy body dementia, Alzheimer's. What to know - USA Today

Patrick Stewart was living with two forms of dementia before his death at 86.

The Emmy-nominated actor and "Star Trek" icon died on Wednesday, Oct. 28, according to a statement shared on Stewart's social media. The post noted that the British actor died at his Los Angeles home while "in the loving care of his beloved wife Sunny, following a brief and poignant journey with Alzheimer's disease and Lewy body dementia."

"He has been held in the warm embrace of family and friends, surrounded by live music, prayer, tears, laughter and the kind of profound emotion that only he could inspire after a lifetime of devotion to us all," the statement continued. "He will be remembered for the dignity, compassion and humanity he brought to every role – in his art and life."

Lewy body dementia and Alzheimer's disease are both types of brain disorders that cause a person's cognitive functioning to deteriorate over time.

Here's what to know about the conditions.

Lewy body dementia, also known as LBD, is the second most common form of progressive dementia behind Alzheimer's disease, according to the Mayo Clinic.

The condition occurs when certain proteins, called Lewy bodies, build up in brain cells and "damage parts of your brain that control thinking and memory," per the Cleveland Clinic. While it's unclear why some people get LBD and others don't, the Mayo Clinic notes a few factors seem to increase the risk, including age, sex and family history.

Other famous faces have also suffered from Lewy body dementia, including the late comic and actor Robin Williams, as well as CNN founder Ted Turner.

Lewy body dementia has no known cure, but medications and therapies can help manage symptoms for a while. Individuals with LBD may live anywhere between two to 20 years from diagnosis to death, according to the National Institute of Neurological Disorders and Stroke.

Some medications typically used for Parkinson's disease and Alzheimer's disease may help with symptoms relating to cognition or movement, but there are many risks attached, per the National Institute of Neurological Disorders and Stroke.

Alzheimer's disease is a neurodegenerative disorder characterized by abnormal biological processes in the brain that often lead to cognitive decline. Symptoms can include forgetfulness, difficulty finding words and struggles with reasoning, problem solving and judgment.

While some of these symptoms may be mild at first, Alzheimer's disease continues to damage the brain, which usually leads to more severe cognitive and functional decline.

While often associated with dementia, Alzheimer's is a specific disease and the most common cause of dementia.

Meanwhile, dementia is a broader "umbrella term that describes a collection of cognitive, functional and behavioral symptoms that are caused by a variety of specific diseases," Courtney Kloske, director of scientific engagement for the Alzheimer's Association, previously told USA TODAY.

One reason the medical terms are often used interchangeably is because Alzheimer's disease is the most common and most heavily researched form of dementia. And new treatments aimed at slowing its progression often bring it into the spotlight, sometimes blurring the lines between the diseases in everyday use.

There's no cure for dementia nor Alzheimer's disease, but treatments are improving, with early detection and new medications offering patients and their families more reasons to hope.