Rhythmicity of activity linked to bipolar mania

Circadian rhythm disturbances are associated with bipolar disorder, and particularly with mania, indicate study findings.

“The results suggest that a greater severity of manic symptoms is related to a less robust circadian rhythm,” reports the team, led by Robert Gonzalez (Texas Tech University Health Sciences Center, El Paso, USA).

This was the result of a lower degree of rhythmicity, as measured by 24-hour autocorrelation, and less robust rhythms of locomotor activity according to circadian quotient variables.

Other clinical characteristics of bipolar disorder associated with rhythm disturbances, measured via actigraphs worn continuously for a week, included disruption in content of thought and thought disorder, increase in rate and amount of speech and increased motor activity and energy.

There was also an association with a decreased need for sleep, suggesting a shared pathophysiology between sleep disruption and circadian rhythm disturbance, says the team.

Rhythm disturbances were not associated with depression, however. This could suggest a mood state phenomenon, say the researchers, but it could also reflect a decreased acuity of actigraphy to define circadian rhythm disturbances.

Circadian rhythm disturbances in the 42 participants did not differ between the 33 who were medicated and the nine unmedicated patients, despite the latter having worse symptoms on the Young Mania Rating Scale.

“These findings suggest that there may be other factors related to the manic state that more closely correlate with disturbances of rhythm,” say Gonzalez et al.

They advise that the correlation between biological rhythm disturbance and bipolar mania does not necessarily imply causation because, while influenced by the central circadian pacemaker, it is also affected by other variables and is therefore not considered a robust marker for the central circadian clock.

“Overall, our study supports the concept that there is significant mood instability associated with affective states in bipolar disorder,” they conclude.

“Ambulatory monitoring of activity patterns in conjunction with other chronobiological biomarkers may be valuable assessments that could potentially serve as physiological biomarkers of the illness and could lead to potential refinement of endophenotypes in bipolar disorder.”

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