Hollywood actor Robin Williams, who hung himself at his home earlier this week, has been diagnosed with Parkinson's disease. Now, researchers have confirmed the suspicion that depression is a very common symptom in people suffering from Parkinson's disease.

In fact, depression is the most prevalent non-motor symptom of Parkinson's - a chronic neurodegenerative disorder typically associated with movement dysfunction, according to a new study by Northwestern Medicine investigators in collaboration with the National Parkinson's Foundation (NPF).

To reach this conclusion, Danny Bega, an instructor in the Ken and Ruth Davee Department of Neurology at Northwestern, analysed data from more than 7,000 patients with Parkinson's disease followed over a one-year period. "Nearly a quarter of the people in the study reported symptoms consistent with depression," Bega observed.

This is important because previous research has determined that depression is a major determinant of overall quality of life. Using the NPS's patient database, the investigators looked at records of more than 7,000 people with Parkinson's disease.

Among those with high levels of depressive symptoms, only one-third had been prescribed antidepressants before the study began, and even fewer saw social workers or mental health professionals for counselling.

The investigators then focused their analysis on the remaining two-thirds of patients with depressive symptoms who were not receiving treatment at the start of the study.Throughout a year of observation, less than 10 percent of them received prescriptions for antidepressants or referrals to counseling.

"The majority of these patients remained untreated. Still, the physician recognition of depression in this population was actually better than previous reports had suggested," Bega noticed.

Physicians must be more vigilant about screening patients for depression as part of a routine assessment of Parkinson's disease, the study, published in the Journal of Parkinson's Disease, concluded.