The cause of cyclothymic disorder is unknown. Although mood swings are irregular and abrupt, the severity of the mood swings is far less extreme than in people with bipolar disorder (manic-depressive illness). Unlike bipolar disorder, periods of hypomania do not turn into mania, in which the person may lose control over his or her behavior and go on spending binges, engage in risky sexual behavior, or drug use and lose touch with reality.
Hypomanic periods are energizing and can result in productivity for some people, while for others these periods can cause impulsive and callous behavior, which can damage relationships. Because hypomania feels good, people with cyclothymia may not seek treatment.
To understand the causes of cyclothymia, it may be useful to explore the causes of bipolar disorder.
Most scientists now agree that there is no single cause of bipolar—rather, many factors act together to produce the illness.
Because bipolar disorder tends to run in families, researchers search for specific genes that may increase an individual's chance of developing the illness. But genes are not the whole story. Studies of identical twins, who share all the same genes, indicate that both genes and other factors play a role in bipolar disorder. If bipolar disorder were caused entirely by genes, then the identical twin of someone with the illness would always develop it, and research has shown that this is not the case. But if one twin has bipolar disorder, the other twin is more likely to develop it than is another non-twin sibling.
