Individuals at high risk for hypomania have alterations in sleep and circadian activity similar to those seen in bipolar disorder patients, indicating that such phenomena are not simply an artefact of the illness, conclude UK researchers.

It is common for bipolar disorder patients to experience sleep and circadian rhythm disturbances, which are associated with illness severity and recurrence. However, the premorbid occurrence and significance of such disturbances is not known.

Steven Jones (Lancaster University) and Dave Ankers (South Staffordshire and Shropshire Healthcare NHS Foundation Trust) studied 31 individuals at behavioral risk for hypomania, as measured on the Hypomanic Personality Scale (HPS), and 24 age- and gender-matched healthy controls.

The participants wore an actigraph for 7 days to obtain sleep and circadian activity data, and completed the HPS, the Hypomanic Interpretations Questionnaire (HIQ), the Internal State Scale (ISS), and a sleep diary.

At-risk individuals scored significantly higher than controls on the HIQ, with the results indicating that not only did at-risk participants make more positive self-referent appraisals for hypomania-relevant experiences than controls, but alsohad more of those experiences.

The team also found that at-risk individuals had a significantly reduced relative amplitude of activity cycle than controls, at 0.81 versus 0.86, suggesting that there was a smaller difference between the most active and least active periods in a day.

Hypomania-risk participants had a significantly shorter sleep duration than controls, at 6:53 versus 7:28 h:m, as well as significantly more variable sleep duration, fragmentation of sleep, and sleep efficiency. They also reported significantly later bedtimes than controls, at 1:20 versus 0:16 h:m.

The team writes in the Journal of Clinical Psychology: “This study found some evidence that circadian markers do differ in those putatively at risk for bipolar disorder when compared with controls.

“This may indicate that circadian differences exist prior to illness onset and could, therefore, represent a core vulnerability for the disorder.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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