Epidemiology

Bipolar disorder is an uncommon condition in children that becomes more frequent in teens, approaching the rate of frequency seen in adults.[19][20]

A large US community study of 13 to 18 year olds (National Comorbidity Survey Adolescent Supplement) reported a lifetime prevalence of 2.5% for bipolar I and bipolar II disorders combined, which is similar to rates found in adults.[21][22] The prevalence of mania was 1.7%, with a twofold increase in rates of mania between the ages of 13-14 to 17-18 years. With regard to pre-adolescence, the US Great Smoky Mountains Study did not identify any cases of mania.[23] Overall, both sexes are equally affected, but early onset cases with comorbid ADHD are predominantly male.[18]

A relative lack of international epidemiologic data, together with methodologic differences, such as the application of diagnostic instruments, has made global comparisons difficult.[24][25] A meta-analysis of the existing international studies of pediatric bipolar disorders for young people ages 7 to 21 years reported an overall rate of 1.8%, and a rate of 1.2% for bipolar I. Higher rates were reported in older samples (2.7% for those ages 12 and above). Although US studies had the widest range of rates, there were no significant differences in mean rates between US and non-US samples, in contrast to the widely held view that this disorder may be over-represented in the US.[20] Higher estimates came from studies that included broader definitions of bipolar disorder. In addition, this study did not find an increase in rates of bipolar disorder in the community over time. In contrast, in clinical samples there appears to be a wide variability in reported rates between international centers. For example, high clinic rates of mania (16%) have been reported in specialist US ADHD centers, although lower rates (6%) have been found in community mental health settings.[26][27] This is in contrast to UK clinic data, where prepubertal mania appears to be very rare (0% to 0.3%) and prevalence of adolescent bipolar disorder is also low (up to 1% reported).[28][29][30] A survey of 200 UK children and adolescents with ADHD only reported one case of bipolar disorder not otherwise specified (BD-NOS).[30] One survey carried out in the US and England reported a 72.1-fold difference in discharge rates for bipolar disorder in young people ages 1-19 years (US: 100.9 per 100,000 population versus England: 1.4 per 100,000 population). After controlling for cross-national differences in length of stay, discharge rates remained 12.5 times higher in the US than in England. For all other child psychiatric diagnoses, the discharge rate was 3.9-fold higher, and for adults with bipolar disorder was 7.2-fold higher, in the US than in England.[31] Differences between clinical studies are likely to be a result of the differing approaches to diagnostic ascertainment in young people.[10]

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