ADHD has a high prevalence of comorbidity with bipolar disorder. Rates of ADHD comorbidity in bipolar disorder have been estimated between 9.5% and 21.2%, and rates of comorbid bipolar disorder in ADHD at 5.1% and 47.1%.
Characteristics of the manic or elevated phase of bipolar disorder that overlap with ADHD include restlessness, talkativeness, distractibility, and fidgeting. The distinctive features of bipolar disorder, largely characterized by the depressive phase, as well as the episodic course of symptoms, can help to elucidate a differential diagnosis.
Several studies have suggested that comorbid ADHD hastens an earlier age of onset of bipolar disorder. In one study, 65% of individuals with ADHD had an early onset of bipolar disorder (at under 18 years of age), compared with only 20% of individuals who did not have comorbid ADHD. Other studies have reported that bipolar patients with comorbid ADHD experienced an earlier average age of mood disorder onset by 5 years or 6 years compared to individuals without ADHD.
In addition to an earlier age of onset, bipolar individuals with comorbid ADHD have demonstrated worse overall course of illness with shorter periods of wellness, more frequent episodes of mania and depression, and a higher instance of additional comorbid psychiatric conditions including anxiety and substance use disorders.
Questions regarding the role of stimulants in bipolar depression remain unresolved. The use of long-acting stimulants in individuals with ADHD and bipolar disorder has been advocated by some once mood has been stabilized with an appropriate mood stabilizer. Still, concerns remain regarding the potential increased risk of stimulant-associated mania/hypomania in bipolar disorder patients. Katzman, M. A., Bilkey, T. S., Chokka, P. R., Fallu, A., & Klassen, L. J. (2017). Adult ADHD and comorbid disorders: clinical implications of a dimensional approach. BMC Psychiatry, 17(1).
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