We used data from a 20-year community follow-up study to investigate the extent to which youth irritability is a risk for adult psychiatric disorders. Parent-reported irritability in youths at a mean age of 13.8 years predicted major depression, dysthymia, and generalized anxiety disorder at 20-year follow-up, even after adjustment for baseline emotional and behavioral disorders. The prediction of major depression and dysthymia from irritability is unlikely to be due to item overlap, since irritability is not a criterion for these diagnoses in adulthood. However, the possibility of item overlap cannot be excluded for generalized anxiety disorder. Irritability at baseline predicted lower educational achievement and income at follow-up; this relationship was direct and not mediated through major depression, generalized anxiety disorder, or dysthymia at follow-up. We also found that only parent-reported, but not self-reported, irritability predicted later psychiatric outcomes. Finally, we compared irritability and arguing and found that the prediction of depressive disorders and generalized anxiety disorder was specific to irritability.
Irritability was associated with a wide range of youth psychiatric disorders cross-sectionally. However, as hypothesized, in spite of irritability's diffuse cross-sectional associations, its longitudinal predictions were specific, in that it increased the risk only for depressive disorders and generalized anxiety disorder. A one-standard-deviation increase in adolescent irritability nearly doubled the risk of generalized anxiety disorder 20 years later, even after adjusting for emotional disorders at baseline. The adjustment for baseline psychopathology using scaled symptoms of major depression or oppositional defiant disorder attenuated the prediction of irritability to major depression at 20-year follow-up, rendering it nonsignificant, perhaps because of overlap of oppositional defiant disorder symptoms with irritability items. However, irritability remained predictive of generalized anxiety disorder and dysthymia even when baseline symptoms were controlled for. Our results also show that adolescent irritability is associated with lower income and educational attainment in adulthood; this relationship is not mediated by major depression, generalized anxiety disorder, or dysthymia at follow-up. Notably, irritability did not predict adult bipolar disorder or any axis II disorder, even in models unadjusted for baseline psychopathology.
Our second hypothesis was that irritability, defined as temper tantrums and anger, would predict depressive disorders or generalized anxiety disorder in adulthood but that arguing with others would not. Irritability and arguing are both symptoms of oppositional defiant disorder, but in previous work (11
) we found that irritability forms a dimension of oppositional defiant disorder that specifically predicts depressive disorders and generalized anxiety disorder. Conversely, symptoms such as arguing with others appear to form a headstrong symptom-dimension of oppositional defiant disorder that predicts ADHD and conduct disorder but not emotional disorders (11
). We found that despite a high correlation between arguing and irritability at baseline, irritability, rather than arguing, predicted later depressive disorders and generalized anxiety disorder. The data presented here add to a growing body of literature (11
) suggesting that irritability and arguing in youth, both of which are components of oppositional defiant disorder, may have differential predictions. This distinction may be relevant for pathophysiological studies of youth oppositionality.
Several points about irritability are worth noting when considering its relationship with psychiatric disorders. The hallmark emotion of irritability—anger—is thought to be one of the earliest appearing in human development (23
). Anger is also thought to occupy a central position between internalizing and externalizing problems. While anger and fear together are regarded as part of a negative affect personality dimension (24
) that is a risk factor for internalizing problems (26
), in factor analyses anger also separates from fear (27
) and predicts externalizing, aggressive behaviors (26
). In particular, irritability appears to be associated with a specific, impulsive form of hostile behavior (30
) that may be differentiated from other forms of aggression by quantitative-genetic (31
) and neurobiological findings (32
). These data suggest that irritability occupies a position at the interface between emotional and disruptive behavior problems.
Our results show that irritability is significantly associated with both emotional and behavioral disorders cross-sectionally during adolescence but is related only to depressive disorders and generalized anxiety disorder at age 33. This could suggest that the relationship between irritability and behavioral problems is pronounced in adolescence and diminishes thereafter, while the link between irritability and emotional problems persists. Alternatively, these results might be explained by the lack of an adult equivalent of oppositional defiant disorder. That is, adults with depression and anger episodes might receive a diagnosis of depression (33
), whereas such a presentation in youth might lead to the diagnoses of both oppositional defiant disorder and major depression. In this context it is important to note that intermittent explosive disorder, a disorder that appears to occur frequently in the general population (7
), is strongly associated with mood and anxiety disorders, suggesting a link between impulse control and affect regulation in adults. Unfortunately, the present study did not ascertain intermittent explosive disorder. It seems particularly important that future longitudinal studies collect data on intermittent explosive disorder outcome and on adult measures of irritability. This would help in establishing whether the prediction from baseline to depressive disorders and generalized anxiety disorder is mediated by the persistence of irritability into adulthood.
Our study has a number of limitations that should be taken into account. First, our irritability scale consisted of only three items and thus had only modest internal consistency, which constrained the upper bound of the predictive value (35
). However, the fact that such a short scale strongly predicted a specific set of disorders over 20 years could be seen as evidence of the robustness of the construct. Second, while some participants were lost to follow-up, the attrition rate is well within what is considered reasonable for such a long follow-up period, and we used a multiple-imputation approach to minimize the likelihood of inaccurate estimates.