Parkinson's disease affects brain cells called the substantia nigra, which produce the chemical dopamine. Dopamine helps control movement; when levels of the chemical are substantially reduced, movements get garbled.
Approximately 1 million Americans have Parkinson's disease. It's usually diagnosed in people age 50 or older, although it's sometimes found in people in their 30s and 40s. The cause is unknown.
"The depression is part of the illness, not simply a reaction to the disease," says Richards in the news release.
Of depressed Parkinson's disease patients, about half have "major" depression that significantly affects their lives. Others have milder symptoms, which are still serious.
Mood and Movement Disorders
Other research shows there may be a link between depression and movement disorders.
Richards and Emory University psychiatrist William McDonald, MD, recently wrote about the possible connection in the journal Neurology.
The pair reviewed a study about depression and a painful involuntary movement disorder called dystonia.
The study, by Gary Heiman, PhD, of Columbia University, and colleagues focused on a mutation of the dystonia gene DYT1.
Heiman's team found that people with a mutated DYT1 gene had increased risk for recurrent major depression. They say that the depressive disorder in these people occurs at an earlier age than people without the gene mutation. They say depression is not the result of having dystonia.
Heiman's study was small, but Richards and McDonald say if larger studies confirm the findings, it could point to a link between disorders of movement and mood.
People with Parkinson's disease may respond differently to the medications than other people, since the disease affects their brains.
Meanwhile, Richards encourages Parkinson's patients to discuss depression with their doctors.
"Many patients assume that it's normal to feel this way," she says. "They might say, 'If you had Parkinson's disease, you'd feel this way too.' That's not true."
"If you treat the depression, they'll still have other symptoms of the disease, but they feel better. It's one aspect of the disease that may be very treatable."