Anxiety Disorders and ADHD: Comorbidity the Rule, Not the Exception

If you work in an anxiety disorder clinic or adult outpatient psychiatric clinic, you probably see a higher prevalence of patients with ADHD than you would in the general population.

Speaking during the Scientific and Clinical Report Session on attention spectrum disorders, Michael Van Ameringen, MD, FRCPC, Co-Director of the Anxiety Disorders Clinic at McMaster University Medical Center in Canada and Associate Professor in the Department of Psychiatry and Behavioral Neuroscience at McMaster University, summarized some of the medical literature on anxiety and ADHD prevalence.

He then described a study of 264 consecutive patients referred to the Anxiety Disorders Clinic in Hamilton, Canada. The patients completed the Adult ADHD self-report scale and were assessed with the Structured Clinical Interview for DSM-IV (SCID-I) and the ADHD module of the Mini International Neuropsychiatric Interview (MINI).

Of the patients referred for anxiety, the prevalence of lifetime ADHD was 37.5% (48.5% male, 51.5% female, p<0.05). “The prevalence of lifetime ADHD was higher in our anxiety disorders clinic than that found in the general population,” he concluded.

Among those with ADHD, comorbidity was the rule rather than the exception. ADHD was significantly associated with a primary diagnosis of impulse control disorder and bipolar disorder and most commonly associated with social phobia (57.6%, NS) and major depressive disorder (56.6%, NS).

Despite meeting DSM-IV criteria for lifetime ADHD, Van Ameringen noted that most patients in the study had never been given a diagnosis or treatment. Seventy-six percent (75/99) of those diagnosed with adult ADHD on the MINI had never received a prior diagnosis and only 17.2% had received ADHD treatment before the study.

When asked which disorder should be treated first when a patient has both ADHD and anxiety, Van Ameringen responded: “I would treat the most impairing condition first.”

Another study, this one conducted by Robert Kayser, MD, Staff Psychiatrist for the US Department of Veterans Affairs, examined the prevalence of ADHD and comorbid psychiatric disorders among patients at an outpatient clinic in Tucson, Arizona. 

The prevalence of ADHD in the general adult population, he said, is estimated at 4.4%, but the prevalence of ADHD in adult outpatient psychiatric clinics is substantially higher-ranging from 17% to 22%. 

Kayser’s recent study sought to determine the prevalence of ADHD among veterans referred by their primary care physicians for psychiatric evaluation in the mental health section of a community-based outpatient clinic as well as to determine the prevalence and types of comorbid psychiatric disorders in these patients with ADHD.

Among the 674 patients (629 males, 45 females) that Kayser personally evaluated between May, 2007 and December, 2010, 23.4% (158/674) had ADHD (22.4% males, 37.8% females).

Among the patients with ADHD, 93% had two or more comorbid psychiatric disorders, including major depression, dysthymic disorder, bipolar disorder, PTSD, panic disorder, and GAD. Forty-one percent (66/158) of those with ADHD were experiencing insomnia and 27.8% (44/158) had sleep apnea. 

My “findings suggest the diagnosis of ADHD may be underrepresented among veterans in outpatient mental health clinics,” he wrote in his presentation summary. “This [finding] could have important prognostic and treatment implications.” He recommended that all veterans seen in mental health clinics be evaluated for ADHD. 

Barriers to diagnosing ADHD in veterans, he said, include denial, an inability to recall childhood behaviors before the age of 7, concern about adversely affecting disability claims for PTSD, and lack of knowledge about adult ADHD and about use of stimulants.

Physician resistance is also an issue, he added, due to the lack of data and training in the diagnosis and treatment of adult ADHD, concern about the use of stimulant medications, restrictive formularies, lack of diagnostic clarity from overlapping symptoms, and the high rate of medical complexity and psychiatric comorbidity among patients with ADHD.