Robin Williams was suffering from the early stages of Parkinson's disease, as well as long-standing depression and anxiety, at the time of his apparent suicide. Here's what experts know about the link between depression and degenerative brain diseases.
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Yesterday, we learned that Robin Williams was suffering from the early stages of Parkinson's disease, as well as long-standing depression and anxiety, at the time of his apparent suicide. Parkinson's and other degenerative brain conditions, like Alzheimer's disease and dementia, have a complicated relationship with depression—they often occur together, experts say, although the link between them is not fully understood.

"It's easy to assume that depression will, of course, affect people with a condition like Parkinson's or Alzheimer's, because they're such difficult and debilitating diseases," says Lisa Shulman, M.D., professor of neurology at the University of Maryland School of Medicine and treasurer of the American Academy of Neurology. "But increasingly it's being recognized that there are actual changes in the brain chemistry that are underlying these depression symptoms."

Take Parkinson's disease, for example: The progressive disorder, which affects up to 1 million people in the United States (most over age 50), is characterized by tremors, slowness of movement, and impaired posture and balance. But, in fact, says Dr. Shulman, recent research has focused less on the disease's well-established motor symptoms and more on its less noticeable ones—including sleep disturbances and mental health problems.

"Depression is often among the very earliest signs of Parkinson's disease," she says. A study published today in the journal Neurology supports this, reporting that "neuropsychiatric symptoms" such as depression, anxiety, and fatigue are more common in newly diagnosed Parkinson's patients than they are in the general population, and that such depression often goes untreated.

About 60% of patients with Parkinson's report having depressive symptoms, and it's estimated that up to 40% of Alzheimer's patients suffer from significant depression, as well.

Part of this link with depression is surely the result of the physical and emotional burdens patients face as their conditions worsen, Dr. Shulman says, but some of it may be triggered by the same brain abnormalities—such as hormone imbalances or genetic mutations—that cause neurodegenerative diseases.

A few studies suggest that depression may actually contribute to some forms of brain disease (like vascular dementia and Alzheimer's disease) because it causes inflammation, alters hormone levels, and damages blood vessels and neurons in the brain. It's possible that treating depression may help reduce the risk of developing brain disease, but more research is needed to clearly establish that link.

But Dr. Shulman says that's not likely the case with Parkinson's disease. "It's true that we should consider, when a person is newly diagnosed with depression, whether there might be other neurologic conditions emerging," she says. "But there's no evidence that depression is an actual risk factor for Parkinson's disease."

Researchers do know that having depression along with a degenerative brain disease can make symptoms of both conditions worse, and more difficult to treat. For instance, depressed Parkinson's patients may be less willing to participate in exercise programs and address movement problems. They've also been shown to have a harder time concentrating than people who are depressed but don't have Parkinson's.

Of course, not everyone with depression will develop a degenerative brain disease, or vice versa. And for those diagnosed with one—or both—of these conditions, there are many effective treatment options to consider.

Medications can help slow the progression of Parkinson's, Alzheimer's, and dementia, and may dramatically improve symptoms of depression. Support groups, counseling, and physical exercise may improve overall quality of life, as well. "In moments like this," Dr. Shulman says, "it's important to recognize that early Parkinson's symptoms and depression are both generally well managed with current therapies."