People with Parkinson disease can be apathetic without being depressed, and apathy may be a core feature of the disease, according to a study published in the July 11, 2006, issue of Neurology, the scientific journal of the American Academy of Neurology.

Apathy is a mental state characterized by a loss of motivation, loss of interest, and loss of effortful behavior. In apathy, the mood is neutral and there is a sense of indifference. In depression, the mood is negative and there is emotional suffering. Because apathy and depression share some of the same symptoms, the disorders can be misdiagnosed.

"This study shows that it's important to screen for both apathy and depression so patients can be treated appropriately," said study author Lindsey Kirsch-Darrow, MS, of the University of Florida in Gainesville. "It will also be important to educate family members and caregivers about apathy to help them understand that it is a characteristic of Parkinson disease. Apathetic behavior is not something the patient can voluntarily control, and it is not laziness or the patient trying to be difficult - it is a symptom of Parkinson disease."

The study compared 80 people with Parkinson disease to 20 people with dystonia, another movement disorder. The researchers hypothesized that apathy would occur more often in people with Parkinson disease, because the disease affects areas of the brain in the frontal cortex that are involved in non-motor activities, whereas dystonia affects areas mainly involved with movement.

Of those with Parkinson disease, 51 percent had apathy, compared to 20 percent of those with dystonia. Apathy with no depression occurred in 29 percent of those with Parkinson disease and none of those with dystonia. The rate of depression was the same in both groups.

Treatments for depression and apathy in people with Parkinson disease are still being evaluated.

The current criteria for diagnosing depression may not be appropriate for people with Parkinson disease, according to neurologist Irene Richard, MD, of the University of Rochester in New York, who wrote an editorial accompanying the study.

"A person with Parkinson disease might be diagnosed with minor depression based solely on the presence of apathy," she said. "The recognition that apathy can be present without depression is important so that we do not inappropriately diagnose and treat a depressive disorder that is not present."

The study is consistent with guidelines issued recently by the American Academy of Neurology recommending that all people with Parkinson disease be screened for and treated for depression, which can affect their quality of life and how well they function.