In a recent study entitled “Postural Control in Bipolar Disorder: Increased Sway Area and Decreased Dynamical Complexity,” Indiana University researchers measured and compared the magnitude of postural sway between study participants with and without bipolar disorder. The study involved 32 participants, 16 of whom carried the bipolar diagnosis. The control group was made up of 16 age-matched non-psychiatric healthy participants. Participants were asked to stand as still as possible on a force platform for 2 minutes under 4 conditions: (1) eyes open-open base (feet apart); (2) eyes closed-open base; (3) eyes open-closed base (feet together); and (4) eyes closed-closed base.

The researchers postulated that because many of the structural, neurochemical, and functional abnormalities identified in the brains of those with bipolar disorder are also implicated in postural control, people with bipolar disorder would have less postural control and hence a greater magnitude of sway than those without a brain disorder. In other words, there’s a connection between motor and mood disorders. The results supported their hypothesis:

• The bipolar disorder group had increased sway area (diminished postural control), especially with the loss of visual information (eyes closed).
• The bipolar disorder group exhibited a loss of complexity – in this case, a diminished ability to make faster, small-scale postural adjustments.

A major complication inherent in the study, as the researchers themselves point out, is that other factors may have influenced the diminished postural control of the participants with bipolar disorder – primarily medication:

“The approach we have chosen for this study, i.e., studying euthymic, medicated patients, clearly presents difficulties in the interpretation of the present results because it is difficult to determine what proportion of the effect size arises from underlying mechanisms associated with bipolar disorder and what effects were due to medications.”

While neuroleptics tend to have a negative effect on sway dynamics, SSRIs and lithium tend to have a positive effect. Another complication consists of variations in the course of illness among the bipolar group and a history of alcohol abuse for some participants. However, even when the researchers accounted for such variations, the results indicated a connection between mood and motor disorders consistent with that of other studies. This suggests that motor disorders may be a core component of bipolar disorder.

The findings here add another layer to the complex neurologic story of bipolar disorder. We have known for a long time that some movement disorders (i.e. Parkinson’s and Huntington’s) have high rates of mood symptoms. This research is working in the other direction – looking at motor symptoms in mood disorder.

While this research does not have immediate or obvious clinical use, it is valuable in evolving our understanding of bipolar disorder as a brain based condition with a variety of associated brain changes. If people with bipolar disorder feel like they are clumsy or uncoordinated, it may be helpful for them to hear that this is likely part of their mood disorder, rather than something they are doing wrong. Perhaps motor based interventions, including exercise or physical therapy, may become more important in the treatment of bipolar disorder or at least in improving quality of life with bipolar.

An additional clinical use that I can think of is that we may eventually use movement symptoms as one piece of data in looking at high risk children, such as those born to people with bipolar disorder, and helping to tease out who among them has higher risk of actually developing the disorder.

Photo by TeeF86, available under a Creative Commons attribution license.

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    Last reviewed: 1 Jun 2011