Attention Deficit-Hyperactivity Disorder (ADHD) is a chronic, developmental psychiatric disorder beginning in childhood and continuing into adulthood with symptoms of inattention, impulsivity and hyperactivity. This disorder can lead to social and academic problems for some individuals in adulthood.^1,2 While Childhood prevalence of ADHD varies between 3 and 12% in the literature, it's prevalence in adulthood is 4 to 5% suggesting that we can estimate that up to 50% of children affected by ADHD continue to endorse the condition during their adulthood.³

H. S. Akiskal conceptualized affective temperaments as precursor phenotypes for the premorbid course of mood disorders on the basis of Kraepelin's dimensional view of manic depressive insanity. Akiskal⁴ suggested that affective temperaments and mood disorders are both genetically transmitted, thereby sharing a common pathophysiological mechanism. Furthermore, some researchers have proposed that temperamental characteristics may be related to the occurrence of mood disoders^5,6 and may have a negative effect on prognosis.⁷

Bipolar disorder (BD) comorbidity rates in adults diagnosed with ADHD have been reported to vary between 9.5% and 27%.^8,9 Patients with both these disorders are reported to exhibit the onset of BD approximately 5 years earlier, show more depressive and mixed episodes generally respond less well to treatment and have more a more severe course of illness.¹⁰ Given the high ADHD comorbidity rates in patients with BD and their relatives, a familial link between these disorders is possible.¹⁰

Up to now, the affective temperamental characteristics of adults diagnosed with ADHD have not been studied. Studies on the relationship between ADHD and temperamental characteristics have been limited to studies on ADHD in childhood. Prior studies on ADHD in childhood have suggested that temperamental characteristics in childhood may be correlated with anxiety and mood disorders,^11,12 and may increase the risk of substance abuse.¹³

A high rate of Bipolar Disorder (BD) comorbidity^14,15 and bipolar symptoms have been found in adults diagnosed with ADHD.^16,17 This has raised the question of whether these two disorders are clinically similar or biologically overlapping.¹⁸ It has not yet been established whether specific temperamental characteristics may have effects that are relevant to diagnosis.

Our study questions are: 1) Do adults diagnosed with ADHD show any specific temperamental characteristics when compared to a healthy control group? 2) Do adults diagnosed with ADHD and those diagnosed with Bipolar Disorder show similar temperamental characteristics?

These individuals diagnosed with ADHD (mean age: 26.5±8.7, 52% male), BD (mean age: 25±4.5, 55% male), and healthy controls (mean age: 28.4±7.4, 57.5% male), were similar in terms of age, sex and educational background (Table 1).

Twenty patients (50%) in the ADHD group were diagnosed with a comorbid mood disorder. Nine (22.5%) with major depression, 9 (22.5%) with bipolar disorder and 2 (5%) with dysthymic disorder. Nine patients in the ADHD group (22.5%) were diagnosed with generalized anxiety disorder, 3 (7.5%) with panic disorder, 3 (7.5%) with obsessive-compulsive disorder, 1 (2.5%) with somatoform disorder, 6 (15%) with alcohol abuse, and 3 (7.5%) with comorbid substance abuse.

In the BD group, 1 patient (2.5%) was diagnosed with comorbid panic disorder, 1 (2.5%) with obsessive-compulsive disorder and 2 patients (5%) with social phobia.

The mean HAM-D, HAM-A and WURS scores of the adults with ADHD were significantly higher when compared to the BD group and the healthy control group (Table 1). The YMRS scores of all the groups were similar. While the mean HAM-A, and WURS scores of the BD group were significantly higher than those for healthy controls, the mean HAM-D and YMRS scores were similar for both groups.

In this study, our aim was to identify the temperamental characteristics of adults diagnosed with ADHD and to compare their temperamental characteristics with those of patients diagnosed with bipolar disorder. To our knowledge, this is the first study investigating affective temperaments in adults diagnosed with ADHD.

All temperament scores (depressive, cyclothymic, irritable, and anxious) except for hyperthymic temperament were higher in patients diagnosed with ADHD and BD as compared to the healthy controls. The hyperthymic temperament scores of patients with ADHD, BD and controls were similar. The most common dominant temperament was irritable temperament for the ADHD group (n=6) and depressive temperament for the BD group (n=12). Our findings for the BD group is not in line with previous studies, which have reported that hyperthymic, cyclothymic and irritable temperaments were prominent in patients with BD.^31,32 Brieger et al.³³ reported that BD patients presenting with mixed episodes exhibited more depressive and anxious and less hyperthymic dominant temperaments. The lower frequency of a hyperthymic temperament and the higher frequency of depressive and anxious temperaments may be related to episode patterns. Additionally, the mean scores for depressive and anxious temperaments seen in the control group were lower than those seen in normal populations, but this was not the case for other temperaments.³⁴ This difference could indicate a significant gap between the scores for the patient and the control groups.

When all patients with ADHD were included in our analyses, the ADHD group scored significantly higher on the irritable temperament scale as compared with the BD group. All other temperament scores were similar.

Because mood disorders may affect temperamental characteristics,³⁵ the same analyses were conducted after excluding all ADHD patients diagnosed with a comorbid mood disorder. Under these conditions the differences on the irritable temperament scale scores disappeared. The similarity we found for "pure" ADHD and BD patients' affective temperament scores is noteworthy, because affective temperaments are regarded to be an endophenotype for BD.

Cognitive impairments are not unusual in patients with BD^36,37 and comorbidity of ADHD and BD is frequent.^8,9,38,39 It is also true that ADHD and BD share many symptoms like irritability and distractibilty.¹⁶ This common pattern suggests that ADHD and BD may share a common neurobiological basis.¹⁸ Our findings tend to support this hypothesis, showing that patients with BD and ADHD tend to share similar affective temperament profiles.

These results should be interpreted cautiously. First, our sample size was small and the temperamental characteristics of our BD group were different from those reported by previous mainstream findings. Second, we did not assess the premorbid personalities of patients diagnosed with BD and ADHD. Because of this, effects from illness or other residual states at the time of assessment cannot be ruled out. In an effort to overcome this limitation, all subjects were assessed according to DSM-IV criteria during a period of full remission from manic and depressive episodes. Third, the affective temperament subtypes were determined by means of a self-report questionnaire. Fourth, the HAM-D and A scores were significantly higher in the ADHD group, and this could affect their performance on the self-rating scale of the TEMPS. Finally, because for adults diagnosed with ADHD comorbidity is the rule rather than the exception, the sample size of our ADHD group without a comorbid mood disorder was particularly small.

Despite these limitations, this study indicates that it may be valuable to take into account the affective temperamental characteristics of patients with ADHD and BD in future studies that consider the clinical distinctions or similarities between these disorders.

Recognizing temperamental characteristics gives us a better understanding of adult ADHD and may help us to develop more accurate definitions of the disorders. In future studies a larger sample size could help to distinguish temperamental characteristics of ADHD subtypes.