Jack Russell, Great White singer, died after a battle with Lewy body dementia. What to know about the progressive disease.

Singer Jack Russell of the band Great White performing onstage.
Jack Russell had recently been diagnosed with Lewy body dementia. (Jill Connelly/AP)

Jack Russell of the band Great White has died at age 63, his family announced Thursday on Instagram. “Jack is loved and remembered for his sense of humor, exceptional zest for life, and unshakeable contribution to rock and roll where his legacy will forever thrive,” his family’s statement reads.

Russell announced in July that he was retiring from touring with the band due to his health. “After a recent diagnosis of Lewy Body Dementia (LBD) and Multiple System Atrophy (MSA), I am unable to perform at the level I desire and the level you deserve,” he wrote. “Words cannot express my gratitude for the many years of memories, love, and support.”

Russell ended his post on this note: “Thank you for letting me live my dreams. You have made my life a wonder.”

Lewy body dementia is one of the most common forms of dementia. It typically begins in people age 50 or older, according to the National Institute on Aging (NIA).

Lewy body dementia, which is the condition actor Robin Williams was diagnosed with before his death, is linked with abnormal deposits of protein in the brain known as Lewy bodies, the NIA explains. “The presence of Lewy bodies disrupts the normal functioning of brain cells and impairs communication between them,” Dr. Verna Porter, neurologist and director of the Dementia, Alzheimer’s Disease and Neurocognitive Disorders at Pacific Neuroscience Institute in Santa Monica, Calif., tells Yahoo Life. That can lead to problems with thinking, movement, behavior and mood, she says.

Multiple system atrophy, which Russell also said he was experiencing, is a progressive neurodegenerative disorder that impacts how a person moves, as well as their blood pressure and digestion, according to the National Institute of Neurological Disorders and Stroke. People with multiple system atrophy usually have a progressive loss of function and are eventually bedridden.

Lewy body dementia is a progressive disease with a survival rate of five to eight years for most people. In the early stages, people with Lewy body dementia can function fairly normally, but as the disease progresses, they need more assistance and eventually depend entirely on others for care, according to the NIA.

There are two types of Lewy body dementia: dementia with Lewy bodies and Parkinson’s disease dementia.

“Lewy body dementia is different from other forms of dementia based on the type of changes in memory and behavior that can be seen,” Dr. Amit Sachdev, medical director in the Department of Neurology at Michigan State University, tells Yahoo Life. “This means that the family will see changes that are more obvious earlier in the disease than would be seen in Alzheimer’s, vascular or other forms of dementia.”

Lewy body dementia can cause various symptoms that may impact a person’s cognition, movement, sleep and behavior. According to the NIA, those can include:

  • Hallucinations

  • Changes in concentration, attention and alertness

  • Muscle rigidity

  • Loss of coordination

  • Trouble swallowing

  • Insomnia

  • Excessive daytime sleepiness

  • Depression

  • Anxiety

  • Paranoia

  • Dizziness

  • Frequent falls

“What sets Lewy body disease apart from other causes of dementia is the prevalence of hallucinations and delusions, as well as a sleep disorder called REM sleep behavior disorder,” Porter says. “The hallucinations of Lewy body disease are typically visual. They may begin with a sense of a presence or shadow, typically in the periphery.”

People with Lewy body disease may also develop delusions, Porter says. “Examples can include paranoid delusions such as a spouse’s infidelity, people stealing from them and delusions of reference, meaning a strong feeling that a person or a place is not what they seem,” she says.

There is no one test to diagnose Lewy body dementia. However, a specialist like a neurologist will usually conduct physical and neurological exams; do blood tests and brain imaging studies to rule out other conditions that could cause similar symptoms; and administer neuropsychological tests to evaluate memory and other cognitive functions, according to the U.S. National Library of Medicine. “An MRI can help in excluding other diseases,” Sachdev says.

Because Parkinson’s disease and Alzheimer’s disease can cause similar symptoms, Lewy body dementia can be hard to diagnose, Sachdev says. Dr. Douglas Scharre, the director of the Center for Cognitive and Memory Disorders at Ohio State University’s Wexner Medical Center, agrees, telling Yahoo Life: “Lewy body dementia is often missed, because a lot of physicians have never heard of it or don’t even know what the symptoms are. Usually people have parkinsonian symptoms — they’re stiff and have balance issues.”

There is no cure for Lewy body dementia. “Instead, we need to try to manage the symptoms,” Sachdev says. Treatment may involve physical therapy, occupational therapy, mental health counseling and medications to help control cognitive, movement and psychiatric issues, according to the NIA.

“We’re now looking at new treatments to help — those are in clinical trials,” Scharre says. “We’re making progress. We’re having medications that may help reduce some of those toxic proteins as opposed to just helping with symptoms.”

According to Russell’s family, details about a public memorial will be shared at a later date.