Bipolar disorder and comorbid attention deficit hyperactivity disorder. A distinct clinical phenotype? Clinical characteristics and temperamental traits.

Objectives: It has been suggested that bipolar disorder (BD) with comorbid ADHD represents a distinct clinical phenotype of BD. There are no data regarding potential heterogeneity between BD subjects with a diagnosis of ADHD in childhood whose ADHD remitted in adulthood (cADHD-BD) vs. BD patients with persistent ADHD diagnosis in adulthood (aADHD-BD). This heterogeneity may constitute a confounder in investigations of the nature of the co-occurrence between BD and ADHD. The aim of this paper is to compare BD patients without ADHD, to those with aADHD-BD, and those with cADHD-BD on clinical and temperamental characteristics, hypothesizing that maladaptive temperament will be increased in BD subjects with a stable diagnosis of ADHD in adulthood compared to those whose ADHD remitted. We further hypothesize that maladaptive temperament will be associated with the severity of both illnesses.

Methods: A total of 100 outpatients (aged 18-30 years) with BD in remission were included. The assessment of ADHD was made according to a procedure aimed to reduce potential recall biases. Subjects had to have a parent available and had never been treated with stimulants. Temperamental traits were assessed with the California Child Q-sort (CCQ) and the Early Adolescent Temperament Questionnaire (EATQ).

Results: Rate of co-occurrence of ADHD-BD was 18% lifetime and 10% current diagnosis. Patients with ADHD-BD (aADHD-BD+cADHD-BD) reported a significantly earlier onset of mood disorder, higher number of previous mood episodes, and significantly higher impulsivity than BD patients without ADHD. aADHD-BD showed a significantly earlier BD onset, higher number of previous mood episodes, higher impulsivity, decreased Reactive Control and higher Negative Emotionality temperamental scores than cADHD patients.

Conclusion: Findings suggest that patients with aADHD-BD present a clinical phenotype distinct from that of patients with BD without ADHD or with a childhood ADHD diagnosis that remitted with the age. This appealing hypothesis of a BD-distinct phenotype that can be detected early due to its associated maladaptive temperamental traits requires further investigation in larger samples, supported by neuropsychological, genetic and imaging data.