Research paperPrevalence of ADHD symptoms across clinical stages of major depressive disorder
Introduction
Worldwide, depressive disorders are highly prevalent, and they have enormous impact on a person’s quality of life (Vos et al., 2012). About 60% of persons with remitted depression experiences recurrence (Solomon et al., 2000), and 24.5% develops chronic depression (Penninx et al., 2011). Furthermore, depression is often comorbid with other psychiatric disorders such as anxiety disorders (Lamers et al., 2011), and attention-deficit/hyperactivity disorder (ADHD) (Kessler et al., 2003). Both depressive disorders and ADHD are heritable (Li et al., 2014, Sullivan et al., 2000), they share many genetic polymorphisms, which might be involved in their etiology (Cole et al., 2009), and they share familial pathophysiological risk factors (Faraone and Biederman, 1997).
In general, the existence of multiple psychiatric disorders negatively impacts the course and prognosis of either disorder (Biederman et al., 2008, van Balkom et al., 2008); they tend to be more severe (Joo et al., 2012), more persistent (Rohde et al., 1991), and are less likely to respond to treatment than “pure” disorders (Bruce et al., 2005). Pediatric epidemiological (Anderson et al., 1987) and clinical studies (Woolston et al., 1989, Biederman et al., 1995, Orvaschel et al., 1988) showed a high prevalence of ADHD symptoms in depression. Conversely, major depressive disorder occurred 5.5 times more often among youths with ADHD than in youths without ADHD (50% vs. 12%) (Angold et al., 1999), and comorbidity rates with depression were even higher in clinical samples of children with ADHD (Pliszka, 1998, Wilens et al., 2002). Epidemiological and cross-sectional clinical studies among adults mirror this link between ADHD and depressive disorders. There is an increased ADHD symptom rate among depressed patients in comparison to controls (5–12% vs. 4%) (Joo et al., 2012, Kessler et al., 2006, Alpert et al., 1996, McIntyre et al., 2010), and a higher prevalence of depressive disorders among ADHD patients (9–25%) than in persons without ADHD (1–8%) (Kessler et al., 2003, Kessler et al., 2006, Chen et al., 2013, Fischer et al., 2007). Also, both referred and non-referred adolescents with ADHD are at risk for developing major depressive disorder (MDD) in adulthood (odds ratio 2.5–2.8) (Biederman et al., 2008, Smalley et al., 2007, Meinzer et al., 2013). Moreover, symptoms of ADHD and depression conceptually overlap, e.g. with regards to concentration difficulties (Association, 1994). Although symptoms overlap between depression and ADHD, the majority of persons with ADHD has shown to maintain their diagnosis when overlapping symptoms with depression were subtracted (Milberger et al., 1995, Barkley and Brown, 2008, Meinzer et al., 2014). Also, hyperactive and/or impulsive behaviors are not part of the diagnostic criteria for depression. For differential diagnosis, it is important that ADHD starts early in childhood and has a chronic course, whereas depression usually starts later and has an episodic course (APA, 2000).
Despite strong cross-sectional (Joo et al., 2012, Simon et al., 2013, Pehlivanidis et al., 2014) and longitudinal indications (Michielsen et al., 2013) of more severe ADHD in depression, and more severe depression in ADHD as compared to general population rates, not all studies endorse this association (Alpert et al., 1996, Biederman et al., 1998, Rasmussen and Gillberg, 2000). A possible explanation may be that various definitions of depression severity have been used, such as symptom severity, duration, burden, and number of depressive episodes. However, none of these definitions take into account the developmental course of depression. Clinical staging models refine the natural course of a disorder into consecutive stages of developmental progression (McGorry et al., 2006, Fava et al., 2007).
We investigated the relationship between ADHD and depression severity using a clinical staging model, in order to test the gradient of increased ADHD symptoms with more severe and persistent levels of depression (Hetrick et al., 2008, Hamilton et al., 2011). The model ranged from pre-clinical stages of persons without lifetime depression diagnosis but with a genetic predisposition, or mild, or more severe depressive symptoms, to clinical stages of current, recurrent and chronic depression. We first analyzed ADHD symptom rates in controls and depressed persons. Next, ADHD symptom rates were assessed across several clinical MDD characteristics that are relevant to staging. Lastly, we investigated ADHD symptom rates across clinical stages of depression. Considering the etiological as well as correlational overlaps between depressive disorders and ADHD symptoms, we hypothesized an increasing prevalence rate of ADHD symptoms in more progressed MDD stages. If confirmed, diagnosing and treating ADHD may be a target for improved treatment results in severe and chronic cases of MDD, that currently have low treatment response rates (Kasper, 2014, Torpey and Klein, 2008).
Section snippets
Study sample
Participants were selected from the ongoing Netherlands Study of Depression and Anxiety (NESDA), a large cohort study investigating the course and consequences of depressive and anxiety disorders among 2981 adults (baseline age range: 18–65 years). The NESDA study started in August 2004 (baseline assessment) by recruiting healthy controls, persons with current or remitted depressive and/or anxiety disorders from the community, primary and secondary care. People from the community and controls
Results
Of the 2053 participants, 181 persons reported ADHD symptoms above the clinical cutoff in adulthood (prevalence rate 8.8%). Prevalence rates of clinical ADHD symptoms were respectively 0.4% (n=2) in healthy controls and 11.4% (n=179) in those with lifetime MDD (remitted or current MDD). Of the 181 persons with clinical ADHD symptoms, 139 (76.8%) had probable ADHD, as they also scored positive on one or more childhood or early-adolescent indicators of ADHD. More specifically, 67.4% of persons
Discussion
This study examined clinical ADHD symptom rates among persons (i) with and without a lifetime depressive disorder, (ii) across categories of clinical characteristics (severity, duration, age of onset, and comorbidity with anxiety) of depression, and (iii) across clinical stages of MDD. To our knowledge this is the first study examining ADHD symptom rates in depression using a clinical staging approach (Dodd et al., 2013, Lin et al., 2013). The relationship between MDD and ADHD is important as
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