A child's temperament is defined as the combination of an underlying biological tendency towards responding to the environment in a particular way and the behavioural responses produced by these tendencies. Children are said to have a difficult temperamental style when they have a high anxiety level; distractibility; withdrawal from, or poor reaction to, new and unfamiliar things; poor adaptability (reacting badly to changes in routine); negative persistence (strong-willed, whiny, rigid) and negative mood (cranky, irritable). More difficult temperaments in childhood have been associated with increased risks for a number of problems including anxiety and mood disorders, early delinquent behaviour, substance abuse, inattention, hyperactivity and aggression. A team of researchers in the U.S. looked into whether there was a link between a difficult childhood temperament and childhood bipolar disorder. They compared 25 children with bipolar disorder, 25 children with Attention Deficit Hyperactivity Disorder (ADHD) and 25 other children with no problems. They found that the children with bipolar disorder had shown more signs of a difficult temperament in childhood than those with ADHD, who had, in turn, shown more signs than the children with no problems. The children with bipolar disorder had had less adaptability to new situations, fewer pleasurable mood states and more irregular body rhythyms than the other children.
West, Amy E., Schenkel, Lindsay S. and Pavuluri, Mani N. - Early childhood temperament in pediatric bipolar disorder and attention deficit hyperactivity disorder Journal of Clinical Psychology April 2008, 64(4), 402-421