What are they key differences between ADHD and bipolar disorder? How can they be identified?
Your patient is a 11-year-old boy who is distracted, hyper, and irritable. He talks excessively in class, and there are signs of impulsivity. Last week he climbed to the roof of the school to throw tennis balls into the parking lot. Is this a case of attention deficit hyperactivity disorder (ADHD), bipolar disorder, or something else? In this slideshow I will look at 7 questions that help clarify the picture.
The DSM criteria are the gold standard for psychiatric diagnosis, but there is a slight problem when it comes applying them to bipolar disorder and ADHD. Most symptoms of ADHD are also seen in mania and hypomania: distractibility, hyperactivity, impulsivity, racing thoughts, excess talking, and irritability. That leaves only 3 manic criteria to tease them apart: expansive mood, grandiosity, and decreased need for sleep. With this much overlap, it is no surprise that 60-90% of children with bipolar disorder are also diagnosed with ADHD.1
It is tempting to think that the condition that starts first is the true diagnosis, but ADHD symptoms are often an early sign of an evolving bipolar disorder.1 The trajectory can be more revealing when the patient reaches adulthood. In bipolar disorder, cognitive symptoms worsen with age and with the number of past episodes.2 In ADHD, they often improve or resolve between ages 18-25.
It is often said that cognitive symptoms are persistent and stable in ADHD, while in bipolar disorder they cycle in and out with the episodes. However, that pearl is starting to show its age. Newer research has found that cognitive problems often persist outside of mood episodes in both children and adults with bipolar disorder.1,2
If the trajectory of cognitive symptoms is only a rough guide, what about the nature of those symptoms? Comparative studies on this question are few, and the differences they have found are small. Euthymic bipolar disorder and ADHD are both associated with problems in working memory, verbal fluency, and executive function. In bipolar disorder, the executive impairments are worse, such as the ability to flexibly respond to changing rules (Wisconsin Card Sort Test), plan a complicated task (Tower of London Test), or filter out irrelevant information (Stroop Task). In contrast, ADHD has more marked impairments in working memory (Digit Span Test) and verbal fluency (“say as many words that begin with the letter S as you can in one minute”).1,3
While those findings bring some clarity to the picture, they only hold up when comparing populations. We are far away from a cognitive test that can reliably separate out individual patients with bipolar disorder from those with ADHD.
Depressive episodes are common in bipolar disorder and ADHD, but they are likely to come on with greater frequency and severity in bipolar disorder. Neurovegetative symptoms like appetite changes, sleep disturbances, and loss of sexual desire are also more prominent in bipolar depressions than those that occur with ADHD.4
What about temperamental symptoms when the patient is not in an episode? Surprisingly, the overlap is even more problematic there. Cyclothymic features like mood lability are common in both disorders, and a history of “trait daydreaming” was identified in a large NIMH study as a sign that a patient with unipolar depression is likely to convert to bipolar disorder.4,5,6
ADHD and bipolar disorder both have a strong genetic basis, so family history can point the way toward the true diagnosis. The Bipolarity Index captures other non-symptomatic markers that can separate bipolar disorder from ADHD, but this scale has only been validated in adults.7
Judgment is difficult and treatment is perilous in these cases, even after the most careful assessment. If you try a stimulant, make sure that it consistently improves their organization, mental status, and overall functioning. Stimulants should have a calming effect in ADHD, quieting the physical and mental restlessness and tempering the irritability and impatience. If the stimulant just enhances energy, mood, or motivation, then the diagnosis is probably not ADHD, and the benefits are likely to wear off after a few months.
1. Zaravinos-Tsakos F, Kolaitis G. Disentangling pediatric bipolar disorder and attention deficit-hyperactivity disorder: A neuropsychological approach. Psychiatriki. 2020;31(4):332-340.
2. Burdick KE, Millett CE, Bonnín CDM, et al. The international consortium investigating neurocognition in bipolar disorder (ICONIC-BD). Bipolar Disord. 2019;21(1):6-10.
3. Walshaw PD, Alloy LB, Sabb FW. Executive function in pediatric bipolar disorder and attention-deficit hyperactivity disorder: in search of distinct phenotypic profiles. Neuropsychol Rev. 2010;20(1):103-120.
4. Torrente F, López P, Lischinsky A, Cetkovich-Bakmas M, Manes F. Depressive symptoms and the role of affective temperament in adults with attention-deficit/hyperactivity disorder (ADHD): A comparison with bipolar disorder. J Affect Disord. 2017;221:304-311.
5. Syrstad VEG, Oedegaard KJ, Fasmer OB, et al. Cyclothymic temperament: Associations with ADHD, other psychopathology, and medical morbidity in the general population. J Affect Disord. 2020;260:440-447.
6. Akiskal HS, Maser JD, Zeller PJ, et al. Switching from 'unipolar' to bipolar II. An 11-year prospective study of clinical and temperamental predictors in 559 patients. Arch Gen Psychiatry. 1995;52(2):114-123.
7. Aiken CB, Weisler RH, Sachs GS. The Bipolarity Index: a clinician-rated measure of diagnostic confidence. J Affect Disord. 2015;177:59-64.