Activity levels may distinguish unipolar from bipolar disorder

By Mark Cowen, Senior medwireNews Reporter

The measurement of activity levels may help distinguish patients with unipolar depression from those with bipolar disorder when they are in a remitted or mild/moderate depressive state, say researchers.

Lars Vedel Kessing (Copenhagen University Hospital, Denmark) and team found that bipolar disorder patients in a remitted or mild/moderate depressive state had significantly lower levels of acceleration (movement) and activity energy expenditure over a monitoring period of more than 72 hours than unipolar patients.

"Our findings confirm that psychomotor retardation is more prevalent in bipolar disorder compared to unipolar disorder when patients are in a remitted or mild/moderate depressive state," comments the team.

In total, 20 unipolar patients, 18 patients with bipolar disorder, and 31 mentally healthy controls participated in the study.

All of the participants, who were aged between 18 and 60 years, were required to wear a combined heart rate and movement monitor for at least 72 hours while performing their normal daily activities and during sleep.

Overall, both patient groups combined had a significantly higher sleeping heart rate, lower fitness, lower acceleration, and lower activity energy expenditure than controls, the researchers report in the Journal of Affective Disorders.

Among the two patient groups, the team found that bipolar patients had significantly lower acceleration levels and activity energy expenditure than unipolar patients, after accounting for age, gender, body mass index, and Hamilton Depression Scale scores.

This difference was particularly evident in the morning between 0600 and 1200, when bipolar disorder patients showed an acceleration reduction of 36% and an activity energy expenditure reduction of 35% compared with unipolar patients.

Kessing et al conclude: "In a remitted or mild/moderate depressive state, bipolar disorder is associated with a substantially lower activity level, compared to unipolar disorder."

They add: "If this difference between groups is replicated in further studies, monitoring of free-living movement may be a promising tool in the diagnosis and distinction between unipolar disorder and bipolar disorder in the remitted to depressive state."

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