Parkinson's Disease May Cause Apathy

GAINSEVILLE, Fla., July 10 -- Apathy independent of depression may be a feature of Parkinson's disease for some patients, researchers here have found.

In a study comparing 80 patients with Parkinson's with 20 others with non-Parkinson's dystonia, half of those with Parkinson's scored positive on a validated test for apathy, compared with only one-fifth of the patients with dystonia, reported Lindsey Kirsch-Darrow, M.S., and colleagues of the University of Florida in Gainesville in the July 11 issue of Neurology.

Apathy could be a core feature of Parkinson's disease independent of depression, the investigators contended.

"This study shows that it's important to screen for both apathy and depression so patients can be treated appropriately," said Kirsch-Darrow. "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."

Unlike depression, which has a negative component, apathy is distinguished by a lack of motivation with behavioral, cognitive, and affective features.

"The behavioral domain includes lack of effort, lack of productivity, and dependence on others to structure activities," the authors wrote. "The cognitive domain includes loss of interest in new experience and lack of concern about one's problems. The affective domain includes flattened affect and lack of response to positive or negative events."

"Emphasized is the primary lack of motivation that is not purely accounted for by intellectual impairment, emotional distress, or diminished consciousness such as drowsiness or delirium," they added.

To determine whether apathy in patients with Parkinson's is a feature of associated depression or a core feature of the disease on its own, the investigators recruited 80 patients with Parkinson's and 20 patients with primary idiopathic adult-onset dystonia.

They volunteers were given the Marin Apathy Evaluation Scale, Beck Depression Inventory, and Centers for Epidemiologic Studies-Depression Scale.

They found a significantly higher severity and frequency of apathy in participants with Parkinson's disease compared with dystonia controls. In all, 51% of patients with Parkinson's scored positive for apathy on the Marin Apathy Evaluation Scale, compared with 20% of controls. In addition, patients with Parkinson's had significantly higher mean scores than controls, indicating a greater degree of apathy among the former.

In addition, apathy without depression was seen in 28.8% of patients with Parkinson's disease, but none of the dystonia controls.

The authors hypothesized that apathy may occur more frequently among people with Parkinson's disease than those with dystonia because Parkinson's may have a greater disruptive effect on frontal subcortical systems such as the anterior cingulate-mesial frontal cortex that are thought to be involved in apathy.

"This study highlights the fact that patients with Parkinson's disease can be apathetic without being depressed," wrote Irene Hegeman Richard, M.D., an associate professor of neurology and psychiatry at the University of Rochester (N.Y.), in an accompanying editorial.

"This raises the concern that the current criteria for diagnosing depression as outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), which considers 'loss of interest or pleasure' a cardinal feature of depression, may not be appropriate for patients with Parkinson's disease," she continued.

Before rushing in to treat patients with Parkinson's disease who display signs of apathy, Dr. Richard wrote, clinicians and family members should consider whether the treatment is in the best interests of the patient, or of his loved ones who are distressed to find that he has lost interest in life.

"Patients themselves generally do not complain of apathy because, by definition, they do not care and are comfortable not engaging in many activities," she wrote. "It is likely that the patients themselves may not have strong feelings about whether or not a medication is indicated to motivate them."

Kirsch-Darrow and colleagues acknowledged that their study was limited by an inability to find controls who were well-matched with cases in terms of demographics, and by the use of diagnostic checklists rather than structured interviews.

In addition, "patients with Parkinson's disease were treated with dopaminergic agonists and levodopa, whereas dystonia patients were not," they wrote. "Although this is an important difference to consider, it is unlikely that dopamine-containing drugs caused increased apathy in the patients with Parkinson's disease. This is because dopamine agents have shown preliminary support for the treatment of apathy."