Impulsivity differences between bipolar and unipolar depression.

BACKGROUND: Even though particularly bipolar depression and unipolar depression seem to be similar, they show differences in terms of the etiology, phenomenology, course, and treatment process. Bipolar depression is associated with mood lability, motor retardation, and hypersomnia to a larger extent. Early age of onset, a high frequency of depressive episodes, and history of bipolar disease in the family are suggestive of bipolar disorder (BD) rather than major depression. Bipolar and unipolar disorders are also associated with increased impulsivity during illness episodes. However, there is little information about impulsivity during euthymia in these mood disorders. The aim of this study was to illustrate the difference in impulsivity in euthymic bipolar and unipolar patients.
MATERIALS AND METHODS: Impulsivity was evaluated by the Barratt Impulsiveness Scale (BIS-11A), in 78 interepisode BD patients, 72 interepisode unipolar disorder patients, and 70 healthy controls. The diagnosis was established by severe combined immunodeficiency. One-way between-groups ANOVA was used to compare the BIS-11A mean scores for all three groups.
RESULTS: Impulsivity scores of the bipolar and unipolar disorder patients were significantly higher than controls on total and all subscales measures. There was no difference between the bipolar and unipolar disorder groups on total, attentional, and nonplanning impulsivity measures. However, BD patients scored significantly higher than the unipolar patients on motor impulsivity measures.
CONCLUSIONS: Both interepisode bipolar and unipolar disorder patients had increased impulsivity compared to healthy individuals. There was no significant difference on attention and nonplanning impulsivity subscales; however, on the motor subscale, bipolar patients were more impulsive than unipolar disorder patients.

INTRODUCTION

Among the mood disorders, bipolar depression and unipolar depression seem to be similar; however, they differ in terms of course, severity, symptom distribution, and treatment process. It is important to identify distinctive features and predictors of these two disorders.

There is no pathognomonic feature or biomarker that can reliably differentiate bipolar depression from other psychiatric disorders, particularly unipolar major depressive disorder (MDD).[12] Consequently, several studies have been reported about sociodemographic and clinical features that can help clinicians in the diagnostic process.[3456]

The distinction between unipolar and bipolar diseases was established in the studies of Pierre Falret (1851) and Jules Baillarger (1854) and then Angst (1966), Peris (1966), and Winokur et al., (1969) who showed nosological differences between bipolar and unipolar disorders in terms of their clinical, genetic, and course features. In addition, there were many corresponding areas between the two disease groups, which raised the question of the presence of possible clinical subtypes between depressive and manic edges of affective diseases.

Bipolar disorder (BD), which may be difficult to diagnose, is often misdiagnosed as recurrent MDD. While diagnosing major depressive episode, clinicians should check if there is a history of mania or hypomania, which is indicative of BD rather than MDD. Bipolar depression is associated with mood lability, motor retardation, and hypersomnia to a larger extent.[789] Early age of onset, a high frequency of depressive episodes, family history of bipolar disease are suggestive of BD rather than major depression.[1011] Compared to unipolar depression, the clinical course of bipolar depression is more severe and suicide is more common.

Impulsivity has been defined as a predisposition toward rapid, unplanned reactions to internal or external stimuli, without regard to the negative consequences.[12] Although impulsivity itself is not a psychiatric diagnosis, it is more likely to be present in individuals with certain psychiatric disorders, such as BDs, attention deficit hyperactivity disorder, personality disorders, and substance abuse and dependence.

BD is commonly associated with increased impulsivity, particularly during manic and depressed episodes,[1314] and unipolar depressive disorder (UD) is also associated with increased impulsivity during depressive episodes.[15]

Increased impulsivity adversely affects the course of BD and UD by increasing suicide risk[13151617] and mood instability.[18] In BD, elevated impulsivity during euthymic periods contributes to disruptive behaviors such as reckless driving,[19] substance abuse disorder,[20] and poor adherence to treatment.[21] However, there is a lack of studies evaluating impulsivity in euthymic UD patients, so it is not known whether impulsivity is associated with poor disease course and substance abuse risk as with BD.

Increased impulsivity in BD and UD during the disease episodes as well as in euthymic states supports that impulsivity is related to mood disorders in general.[1822] If this is confirmed, then therapies targeting impulsivity could represent novel interventions for mental disorders with impulsivity at their core, as suggested by Pattij and Vanderschuren.[23]

Therefore, in this study, we compared questionnaire-measured impulsivity in euthymic BD, UD patients, and healthy controls (HCs). BD and UD, which are not the same disorder, have similarities and differences, and their impulsivity characteristics and differences have not been demonstrated yet.

Our hypothesis is that these two disorders differ in terms of clinic, genetics, treatment, and prognosis, therefore have different impulsivity rates and profiles.

We compared the impulsivity differences of BD, UD and controls.

MATERIALS AND METHODS

Participants

Seventy-eight euthymic (interepisode) BD patients, 72 euthymic (interepisode) UD patients, and 70 HC were recruited from the Outpatient Psychiatry Clinic of Sakarya University Faculty of Medicine. BD and UD diagnoses were confirmed using the structured clinical interview for Diagnostic and Statistical Manual of Mental Disorders-IV diagnoses.[24] Mood state defined according to Hamilton Rating Scale for Depression (HAM-D),[25] 21 items, and the young mania rating scale (YMRS).[26] Inclusion criteria consisted of being in remission for 2 months (YMRS score <6 and HAM-D score <8).

The inclusion criteria were as follows:

18 years of age or older

Diagnosis of euthymic BD and UD

No history of axis I disorders for HC.

The exclusion criteria for all groups were as follows:

Presence of chronic illness (e.g., hypertension, diabetes, liver disease, kidney diseases, current thyroid dysfunction, or neurological disease)

Current comorbid axis I disorders.

All procedures were performed after the participants had demonstrated adequate understanding and provided written informed consent.

Methods

The participants completed the BIS version 11A (BIS-11A)[27] to assess impulsivity. The BIS-11A is a 21-item self-report inventory that measures impulsivity as a trait encompassing three domains: attentional impulsivity (intolerance for complexity and persistence), motor impulsivity (tendency to act without forethought), and nonplanning impulsivity (lack of a sense of the future). Items were rated from 1 (absent) to 4 (most extreme).

Statistical analysis

All analyses were performed using the Statistical Package for the Social Sciences, Version 16 for (SPSS, Inc., Chicago, IL, USA). The two groups were compared using one-way between-groups ANOVA. The level of statistical significance was set at P = 0.05. We ran additional subgroup analyses comparing impulsivity in BD and UP with and without suicide attempts and a history of substance use.

RESULTS

Demographic data

Mean ages of BD and UD patients and HC were 35.42 ± 11.15, 39.31 ± 10.92, and 37.19 ± 11.54, respectively. Number of male and female patients in BD, UD, and HC groups were as follows: BD group (M: 36, F: 42), UD group (M: 22, F: 50), and HC group (M: 34, F: 36). Mean years of education of BD, UD, and HC groups were 9.21 ± 3.63, 8.69 ± 4.17, and 10.09 ± 4.06, respectively. The patients did not differ from controls in terms of age, gender, or education. Demographic characteristics of these three groups are shown in Table 1.

Table 1

Demographic characteristics of the groups

	BD (n=78) Mean±SD	UD (n=72) Mean±SD	HC (n=70) Mean±SD	Statistics
Age	35.42±11.15	39.31±10.92	37.19±11.54	f=2.20; P=0.108
Years of education	9.21±3.63	8.69±4.17	10.09±4.36	f=2.13; P=0.121
	BD n (%)	UD n (%)	HC n (%)	Statistics
Male	36 (46.0%)	22 (30.5%)	34 (48.5%)	χ2=5.6; P=0.059
Female	42 (54.0%)	50 (69.5%)	36 (51.5%)
		BD n (%)	UD n (%)	HC n (%)
Marital Status	MarriedSingleDivorced	45 (57.6%)32 (41.1%)1 (1.3%)	52 (72.2%)17 (23.6%)3 (4.2%)	53 (75.7%)17 (24.3%)0 (0%)
Location	RuralUrban	13 (16.7%)65 (83.3%)	16 (22.2%)56 (77.8%)	1 (1.5%)69 (98.5%)

Group comparisons

Age of onset of BD was 27.71 ± 10.06 and age of onset of UD was 35.18 ± 10.24 years. The BD mean HAM-D score was 2.33 ± 1.87, and the mean YMRS score was 2.29 ± 1.79. The UD mean HAM-D score was 3.17 ± 1.73, and the mean YMRS score was 1.78 ± 1.46. Among the BD patients, 11 (14.1%) had attempted suicide versus 12 (16.7%) in the UD sample. Among the BD patients, 8 (10.2%) had past substance use disorders versus 3 (4.2%) in the UD sample. Clinical characteristics of BD and UD groups are shown in Table 2.

Table 2

Clinical characteristics of BD and UD groups

	BD (n=78) Mean±SD	UD (n=72) Mean±SD	Statistics
Number of episode	3.59±3.25	2.42±1.29	t=2.85; P=0.005
Number of hospitalization	2.01±1.35	0.31±0.06	t=9.62; P=0.000
Age of onset	27.71±10.06	35.18±10.24	t=4.50; P=0.000
Duration of illness (years)	7.55±6.25	4.02±3.24	t=3.23; P=0.001
Suicide attempt	118	12	χ2=0.19; P=0.661
Past substance use disorder	2.33±1.87	3	χ2=11.0; P=0.061
HAM-D	2.29±1.79	3.17±1.73
YMRS		1.78±1.46

The BD and UD groups scored similarly on total impulsivity measures [Table 3]. However, the BD and UD groups scored significantly higher than the HC (P < 0.001).

Table 3

Comparisons of BIS 11-A scores of groups

	BD (n=78) Mean±SD	UD (n=72) Mean±SD	HC (n=70) Mean±SD	Statistics
Nonplanning	16.37±3.66	16.19±3.58	13.85±2.44	f=13.00; P<0.001
Motor	21.53±4.70	19.80±4.51	18.04±2.82	f=13.20; P<0.001
Attention	26.29±4.87	26.05±4.94	23.31±4.34	f=8.78; P<0.001
Total	64.37±9.67	62.51±9.44	55.54±6.87	f=20.24; P<0.001

On the nonplanning subscale, the BD and UD groups scored similarly, and both scored higher than the HC (P < 0.001).

On the attentional subscale, the BD and UD groups scored similarly and both scored higher than the HC (P < 0.001).

On motor impulsivity, there were differences between the BD and UD groups. BD group scored significantly higher than UD group (P = 0.029) [Table 4] and both of these groups scored significantly higher than the HC group (P < 0.001).

Table 4

Post hoc Tukey analysis of groups

	BDB-UDB	UDB-HC	BDB-HC
Nonplanning	md=0.17; P=0.949	md=2.33; P=0.002	md=2.51; P=0.001
Motor	md=1.73; P=0.029*	md=1.76; P=0.031	md=3.49; P=0.000
Attention	md=0.23; P=0.760	md=2.74; P=0.001	md=2.98; P=0.000
Total	md=1.85; P=0.401	md=6.97; P=0.000	md=8.82; P=0.000

BIS-11A=Barratt Impulsiveness Scale, version 11A. *P 0=0.029; significant difference between BD and UD on motor impulsivity

DISCUSSION

Impulsivity is associated with the mechanisms and consequences of affective symptoms.[1228] The impulsivity, which is considered to be inherent in mania, is a prominent part of the diagnostic criteria.[2429] There is evidence supporting the presence of a relationship between impulsivity and depression as well as mania. Impulsivity can also be a component of the depressive state itself. Impulsivity appears to be differentially related to depressive and manic episodes. Swann et al. demonstrated that both depression and mania are significantly associated with total and attentional impulsivity.

Mania is associated with motor impulsivity, whereas depression is associated with nonplanning impulsivity. Impulsivity is increased in BD even when patients are euthymic.[1314] Euthymic bipolar patients express impulsivity at higher levels than healthy individuals;[29] however, they do not differ from manic bipolar patients.[30] These findings suggest that the impulsivity found among bipolar patients may be independent of mood state. Our findings confirm previous results of increased levels of impulsivity, even if patients are euthymic.[19313233] Euthymic bipolar patients express higher total and subscale impulsivity scores.

This study specifically investigated impulsivity and its correlations in patients with MDD in an euthymic state and mainly demonstrated that impulsivity, measured using the BIS-11, was substantially higher in participants with MDD compared with healthy participants. In contrast to our findings, Westheide et al.[34] found that patients with major depression did not report increased impulsive behavior compared with healthy individuals. Two previous studies reported that euthymic unipolar patients scored significantly higher than HC only on motor impulsiveness, and they suggested that motor impulsivity may be a trait that differentiates unipolar individuals from healthy ones.[1335] The results of one review by Saddichha and Schuetz found no consistency in the association between depression and impulsivity.[36] They selected studies involving participants with MDD only in remission. A total of five studies reported an association while four studies did not. The results may also be indicative of a contribution of impulsivity in depression too, as the neutral results also showed significant differences in impulsivity, all indicating a higher impulsivity in the groups of individuals suffering from MDD. Hence, our results are important due to the association of impulsivity and MDD.

An association between impulsivity and mood disorders that extend across mood states is important because it would imply that impulsivity is more than the direct expression of mood symptoms in affected individuals. Therefore, the relatively high level of impulsivity found in mood disorders can only be a stable component that is not merely a manifestation of mood state. This association could have different origins: it could be a consequence of repeated mood episodes, a risk factor for the disorder, or a manifestation of an independent factor linked with the biological causes of the disorder. Elevated levels of impulsivity are thought to be core and pervasive feature of both BD and UD. Each of these possibilities could have important implications for a better understanding of bipolar and unipolar disorders.

Henna et al.[32] evaluated impulsivity by the BIS-11A in 54 BD patients, 25 unipolar disorder patients, 136 healthy volunteers, and 14 unaffected relatives. Bipolar and unipolar disorder patients scored significantly higher than the HC and unaffected relatives on all measures of the BIS-11A. In our study, bipolar and unipolar disorder patients scored similarly on total and all three subscales.

In our study, we demonstrated that both interepisode BD and UD had increased total impulsivity. Subscale attention and nonplanning impulsivity were not different; however, on the motor subscale, BD patients were more impulsive than unipolar disorder patients. Motor impulsivity was higher in BD group than UD group. This refers to BD patients who have special feature when they are compared with UD about impulsivity: a tendency to act impetuously. To the best of our knowledge, the current study is the first study which investigated the motor impulsivity difference between BD and UD.

This study has several limitations. We only used one clinical measurement of impulsiveness and did not carry out cognitive assessment. This is a cross-sectional study of baseline parameters; hence, the long-term associations between impulsivity and clinical properties were not addressed. There is a need to examine the longitudinal course of illness in these participants and evaluate the complex interrelationships among impulsivity and sociodemographic and clinical properties as well as the impact of psychopharmacological and psychosocial interventions. There were no controls for anxiety and personality disorders, which have been shown to be associated with high impulsivity.[12] Another limitation is that BD and UD participants in this study were all receiving psychotropic medicines despite being remission because of ethical issues. It is known that lithium, valproate antipsychotics, and antidepressants have anti-impulsive and anti-aggressive effects.[3738394041424344] In our study, it is important to note that despite the use of mood stabilizers, antidepressants, and antipsychotics that reduce impulsivity, the BD patients were more impulsive on the motor impulsivity than UD patients.

CONCLUSIONS

Trait impulsivity was elevated in patients with isolated interepisode BD and UD, confirming that impulsivity is relatively independent of mood state and is higher in BD and UD patients. Interepisode BD and UD patients had increased total impulsivity. On the motor subscale, BD patients were more impulsive than UD patients. Motor impulsivity appeared to be related to BD rather than UD. Hence, these findings should be explored and replicated in larger samples.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.