Bipolar disorder usually strikes between the ages of 15 and 25, and is extremely rare in preteens, according to a major study: Age at onset versus family history and clinical outcomes in 1,665 international bipolar-I disorder patients
The findings are old hat. It's long been known that manic-depression most often begins around the age of 20, give or take a few years. Onset in later life is less common while earlier onset is very unusual.
The main graph could have been lifted from any psychiatry textbooks of the last century:
The red bars are the data. Ignore the black line, that just shows an imaginary 'even' distribution over the lifespan.
Why am I blogging about these remarkably unremarkable results? Because they undermines the theory, popular in certain quarters but highly controversial, that 'child bipolar' or 'pediatric bipolar' is a major health problem.
The study confirmed that early-onset bipolar I does exist, but just 5% of the bipolar I patients had an onset before the age of 15. Assuming a lifetime prevalence of 1% for bipolar I disorder, which is about right, that makes about 0.05%, 1 in 2000 kids, about the same prevalence as Down's Syndrome. Even that's an overestimate, though, because this sample was enriched for early-onset cases: some of the participating clinics were child and adolescent only.
There's a few caveats. This was a retrospective study, that took adults diagnosed bipolar, and asked when their symptoms first appeared. It's possible that early onset cases were under-sampled, if they were less likely to survive to adulthood, or get treated. The generally milder bipolar II might also be different from the bipolar I studied here. But in general, these numbers support the traditional view that childhood bipolar is just not very prevalent.
Baldessarini, R., Tondo, L., Vázquez, G., Undurraga, J., Bolzani, L., Yildiz, A., Khalsa, H., Lai, M., Lepri, B., Lolich, M., Maffei, P., Salvatore, P., Faedda, G., Vieta, E., and; Tohen, M. (2012). Age at onset versus family history and clinical outcomes in 1,665 international bipolar-I disorder patients World Psychiatry, 11 (1), 40-46 DOI: 10.1016/j.wpsyc.2012.01.006
