Attention deficit hyperactivity disorder (ADHD), the most common diagnosis in child psychiatry, appears to be more challenging to diagnose and treat when there is a comorbid depressive disorder. In community samples, estimates of the prevalence of depression among patients with ADHD range from 13% to 27%, while clinical sample reports have run as high as 60%. (1-3) Conversely, among children and adolescents with depression, various studies have reported widely varying rates of ADHD (from less than 5% to more than 50%); a recent study in very young children reported a rate of 42%. (4,5) Nevertheless, ADHD and depressive disorders are often difficult to separate in clinical practice.
Depressed children often show more irritability and inattention than sadness, which may lead to a misdiagnosis of ADHD. (6) Various algorithms and evidence-based treatment recommendations for comorbid ADHD and depression point in somewhat differing directions. (3,7,8) In clinical practice, moderating factors that include age and sex as well as additional comorbid conditions add complexity.
In this article, we review key issues in the diagnosis, treatment, and outcome of comorbid ADHD and depression. We also highlight the importance of moderating variables and consider the validity of the distinction between internalizing and externalizing disorders. Our review of academic studies is complemented with new naturalistic findings from 3419 patients who were routinely assessed at baseline and 4-month follow-up in private practice.
Diagnostic controversies
Some conditions, such as thyroid disease, drug abuse, sleep disorders, learning disabilities, bipolar disorder, or attachment disorders may easily be misdiagnosed as ADHD if not screened for. (6,9) Source bias in the diagnosis of ADHD remains a concern, parent and teacher ratings of schoolchildren are frequently inconsistent, and the validity of the most widely used instrument to diagnose ADHD--the Conners' Rating Scale-Revised--has been seriously questioned. (3,10) DSM-IV split the ADHD diagnosis presented in DSM-IIIR into inattentive and hyperactive/impulsive subtypes, and more recent research suggests other ways of subtyping ADHD (11-13):
* With and without antisocial disorders.
* ADHD alone, ADHD with oppositional defiant disorder/conduct disorder (ODD/CD), ADHD with anxiety, and ADHD with ODD/CD and anxiety.
* Persistent versus nonpersistent ADHD.
Turning conventional wisdom on its head, research findings suggest that from a familial perspective, the assessment of ADHD may be more valid in adults than in children. (14) Such findings can lead to polarized conclusions, including hypotheses that ADHD is genetically heterogeneous or that ADHD is not a disease but rather a group of symptoms that represents a common behavioral pathway for a range of emotional, psychological, and learning problems. (3,13)
Similarly, the diagnosis of depression in children is not without concerns. Historically, clinicians maintained that young children have difficulty naming affect and considered the diagnosis of mood disorders in children controversial. (3,15) However, recent studies show more typical presentations of major depressive disorder (MDD) in children. (5) In addition, there have been widely discrepant reports of the prevalence of depression among children with ADHD. The Multimodal Treatment Study of Children With ADHD (MTA) found mood disorders in only 4% of study participants, which is far...