Low hedonic tone and attention-deficit hyperactivity disorder: risk factors for treatment resistance in depressed adults

Background: The burdens imposed by treatment-resistant depression (TRD) necessitate the identification of predictive factors that may improve patient treatment and outcomes. Because depression and attention-deficit hyperactivity disorder (ADHD) are frequently comorbid and share a complex relationship, we hypothesized that ADHD may be a predictive factor for the diagnosis of TRD. This exploratory study aimed to determine the percentage of undetected ADHD in those with TRD and evaluate factors associated with treatment resistance and undetected ADHD in depressed patients. Subjects and methods: Adults referred (n=160) for psychiatric consultation completed a structured interview (MINI Plus, Mini International Neuropsychiatric Interview Plus) to assess the presence of psychiatric disorders. Results: TRD was significantly associated with the number of diagnoses (P<0.001), past (P<0.001) and present medications (P<0.001), chronic anhedonia (P=0.013), and suicide ideation (P=0.008). Undetected ADHD was present in 34% of TRD patients. The number of referral diagnoses (P<0.001), failed medications (P=0.002), and past selective serotonin reuptake inhibitor failures (P=0.035) were predictive of undetected ADHD in TRD. Conclusion: Undetected ADHD may be more prevalent among TRD patients than previously thought. In addition, TRD patients are more likely to present with psychiatric comorbidity than non-TRD patients. Screening patients with depression for the presence of ADHD and chronic anhedonia/low hedonic tone may help identify patients with TRD and undetected ADHD and improve treatment outcomes.