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The importance of irritability as a symptom of major depressive disorder: results from the National Comorbidity Survey Replication

Molecular Psychiatry volume 15, pages 856–867 (2010)Cite this article

Abstract

Irritability is a diagnostic symptom of major depressive disorder (MDD) in children and adolescents but not in adults in both the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) and International Classification of Diseases (ICD-10) systems. We explore the importance of irritability for subtyping adult DSM-IV MDD in the National Comorbidity Survey Replication (NCS-R), a national US adult household survey. The WHO Composite International Diagnostic Interview (CIDI) was used to assess prevalence of many DSM-IV disorders in the lifetime and in the year before interview (12-month prevalence). MDD was assessed conventionally (that is, requiring either persistent sadness or loss of interest), but with irritability included as one of the Criterion A symptoms. We also considered the possibility that irritability might be a diagnostic symptom of adult MDD (that is, detect cases who had neither sad mood nor loss of interest). Twelve-month MDD symptom severity was assessed with the Quick Inventory of Depressive Symptomatology and role impairment with the Sheehan Disability Scale. After excluding bipolar spectrum disorders, irritability during depressive episodes was reported by roughly half of respondents with lifetime DSM-IV MDD. Irritability in the absence of either sad mood or loss of interest, in comparison, was rare. Irritability in MDD was associated with early age of onset, lifetime persistence, comorbidity with anxiety and impulse-control disorders, fatigue and self-reproach during episodes, and disability. Irritability was especially common in MDD among respondents in the age range 18–44 and students. Further investigation is warranted of distinct family aggregation, risk factors and treatment response. Consideration should also be given to including irritability as a nondiagnostic symptom of adult MDD in DSM-V and ICD-11.

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Introduction

Clinical studies of depressed children and adolescents have shown that the most frequently reported symptom in moderate depression is irritability,1, 2 which is consistent with the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) stipulation that irritability is a diagnostic symptom of major depression in children and adolescents (that is, it detects subjects not detected by sad mood or loss of interest). However, DSM-IV does not include irritability as a symptom of major depressive disorder (MDD) among adults, despite the fact that irritability is commonly found in clinical samples of adults with MDD.3, 4, 5 The clinical literature also suggests that irritability might be a meaningful subtyping variable in MDD, with irritable cases more likely than nonirritable cases to be women, young, unemployed, more severely depressed, lower in functional status and quality of life, and to have a history of at least one suicide attempt.4 These differences could be of considerable importance, because irritability with anger attacks might be present in more than one-third of patients with MDD,6, 7, 8 although the robustness of these results is difficult to assess due to the fact that irritability was not assessed consistently in these studies.

The above results all come from clinical samples. No study, to our knowledge, has investigated the prevalence or correlates of irritability as a symptom of MDD in a general population sample. The current report presents such results from the National Comorbidity Survey Replication (NCS-R),9 with the goal of exploring the importance of irritability as a symptomatic subtyping distinction in a general population sample of people with a lifetime history of MDD.

Materials and methods

Sample

The NCS-R is a nationally representative survey of mental disorders among English-speaking household residents ages 18 and older in the continental United States.9 Interviews were conducted with 9282 respondents between February 2001 and April 2003. Verbal informed consent was obtained before data collection. Consent was verbal rather than written to maintain consistency with the baseline NCS.10 The Human Subjects Committees of Harvard Medical School and the University of Michigan both approved the recruitment and consent procedures. Respondents were paid $50 for participation. The response rate was 70.9%. A probability subsample of respondents that oversampled Composite International Diagnostic Interview (CIDI) cases was administered the lifetime nonpatient version of the Structured Clinical Interview for DSM-IV (SCID)11 to validate CIDI diagnoses. These clinical reappraisal study respondents were given a $50 incentive. A probability subsample of nonrespondents was administered a brief telephone survey and results were used to weight the main sample for nonresponse bias. Nonrespondent survey participants were given a $100 incentive.

The main NCS-R interview was administered in two parts. Part I included a core diagnostic assessment of all respondents (n=9282). Part II included questions about correlates and additional disorders administered to all Part I respondents who met lifetime criteria for any core disorder plus a roughly one-in-three probability subsample of other respondents (n=5692). A more detailed discussion of NCS-R sampling and weighting procedures is presented elsewhere.12

Diagnostic assessment

Diagnoses were based on Version 3.0 of the World Health Organization CIDI,13 a fully structured instrument designed for use by trained lay interviewers who do not have clinical experience. Diagnoses are based on DSM-IV criteria.14 Diagnostic hierarchy rules were applied in making diagnoses. The core disorders assessed in the survey include mood disorders (MDD, dysthymia and bipolar (BP) I and II disorders), anxiety disorders (panic disorder, agoraphobia without panic, specific phobia, social phobia, generalized anxiety disorder (GAD), obsessive–compulsive disorder, posttraumatic stress disorder (PTSD)), substance disorders (alcohol and drug abuse and dependence) and impulse-control disorders (oppositional-defiant disorder, conduct disorder, intermittent explosive disorder (IED)). Age of onset (AOO) was assessed with retrospective self-reports at the syndrome level. The CIDI assessment of major depressive episode (MDE) asked about symptoms in the worst lifetime episode and included a number of symptoms in addition to those specified in DSM-IV. One of these was irritability, which was assessed with a simple yes–no question about whether the respondent was ‘irritable, grouchy or in a bad mood’ most every day during the worst 2 weeks of the index episode. In retrospect, the decision to assess irritability with only a single question was unfortunate, as we could have evaluated the sensitivity of results to different definitions if multiple items had been used. Furthermore, inclusion of the term ‘bad mood’ in the irritability question might have led to some false positives, to the extent that respondents interpreted this term to mean a sad mood, but our impression from subsequent debriefing interviews is that this was not a common interpretation in the context of the earlier terms ‘irritable’ and ‘grouchy’. Other symptoms included in the assessment were euphoria, extreme irritability and several other symptoms of mania–hypomania that were included to distinguish depressive episodes from mixed episodes. CIDI–SCID concordance was found to be good for lifetime diagnoses of MDE (κ=0.59) and excellent for diagnoses of BP spectrum disorder, including BP-I, BP-II and subthreshold BP disorder (κ=0.94).

In addition to diagnosing threshold MDD, the CIDI included an assessment of subthreshold cases, making it possible to calculate how much the estimated prevalence of MDD would increase, if irritability could substitute for sad mood if the latter was not present. Furthermore, in an effort to explore the implications of including irritability as a core symptom of MDD (that is, as a symptom that could substitute for the requirement of either sad mood or loss of interest if neither of the latter was present) among adults rather than only among children and adolescents, a separate assessment of all other symptoms of MDD was made for episodes of irritability in the absence of either depressed mood or loss of interest.

Respondents who met DSM-IV/CIDI criteria lifetime MDD and reported having an episode in the year before the interview (12-month MDD) were administered the Quick Inventory of Depressive Symptomatology Self-Report (QIDS-SR)15 to assess symptom severity in the worst month of the past year. The QIDS-SR is a fully structured measure that is strongly related both to the clinician-administered Inventory of Depressive Symptomatology (IDS-C)16 and to the Hamilton Rating Scale of Depression (HRSD).17 Transformation rules developed for the QIDS-SR18 were used to convert scores into clinical severity categories mapped to conventional HRSD ranges of none (that is, not clinically depressed), mild, moderate, severe and very severe. These respondents were also administered the Sheehan Disability Scales (SDS)19 to assess the extent to which depression interfered with functioning in work, household, relationship and social functions in the worst month of the past year. Responses were scored with a 0–10 visual analogue scale having response options labeled none (0), mild (1–3), moderate (4–6), severe (7–9) and very severe (10).

Analysis methods

Subgroup comparisons were used to study prevalence and correlates of lifetime irritable and nonirritable MDD. Sociodemographic correlates were examined using logistic regression. Age of onset (AOO) distributions were estimated using the two-part actuarial method implemented in SAS.20 Persistence was examined by calculating means of reported years in any lifetime depressive episode and the proportion of lifetime cases who were in an episode in the past 12 months. Twelve-month clinical severity and severity of role impairment were examined by calculating distributions within the irritable and nonirritable depression subgroups. Lifetime comorbidity was assessed by calculating odds ratios (ORs) of lifetime irritable and nonirritable MDD with other lifetime DSM-IV/CIDI disorders. Because the NCS-R sample design used weighting and clustering, all statistical analyses were carried out using the Taylor series linearization method,21 a design-based method implemented in the SUDAAN software system.22 Significance tests of sets of coefficients were made using Wald χ2-tests based on design-corrected coefficient variance–covariance matrices. Statistical significance was evaluated using two-sided design-based 0.05 level tests.

Results

Prevalence, age of onset and persistence

Of the 19.2% of NCS-R respondents who met lifetime criteria for MDE, roughly one-eighth (13.4% of the 19.2%) were classified as having either threshold or subthreshold BP disorder, and another 33.1% reported a lifetime history of core hypomanic symptoms (that is, a distinct period of abnormally and persistently elevated, expansive or irritable mood lasting several days or longer with at least one other symptom of hypomania) (Table 1). Roughly equal numbers of the remaining 53.5% of respondents with lifetime MDE reported either the presence (27.7%; n=489) or the absence (25.8%; n=466) of irritability in their worst lifetime depressive episode, representing 5.3% (irritable MDE) and 5.0% (nonirritable MDE), respectively, of the total NCS-R sample.

Table 1 Disaggregated lifetime prevalence estimates of DSM-IV/CIDI MDE in the NCS-R (n=9282)
Full size table

The estimated lifetime prevalence (with standard error in parentheses) of irritable MDD would increase by 0.6% (0.1), from 5.3% (0.2) to 5.9% (0.2), if irritability was included as a 10th Criterion A symptom and if diagnosis required sad mood or loss of interest along with a total of at least 5 of 10 Criterion A symptoms (rather than the requirement of at least 5 of 9 in DSM-IV). If irritability was included as a diagnostic symptom of adult MDD, so that episodes of irritability in the absence of either sad mood or loss of interest qualified for a diagnosis so long as they were accompanied by at least four other DSM-IV Criterion A symptoms and all other DSM-IV criteria, lifetime prevalence of irritable MDD would increase by another 0.5% (0.1) to 6.4% (0.6). To put this last point in perspective, only 28 additional people out of a sample of 9282 would meet lifetime criteria for MDE and not for major depression if we allowed irritability to be a diagnostic symptom of adult MDD.

Mean retrospectively reported AOO of DSM-IV MDD (that is, excluding the two kinds of exploratory cases described in the previous paragraph, neither of which meets DSM-IV criteria) was found to be significantly earlier for irritable (26.7 years) than nonirritable (31.3 years) cases (F1,953=13.7, P<0.001; Table 2). The shape of the AOO distribution is nonetheless generally consistent for the two subtypes (Figure 1). The estimated mean number of years in any lifetime episode is also similar for irritable and nonirritable MDD (5.7 vs 5.1, F1,953=0.1, P=0.75), although persistence, as indirectly indicated by the ratio of 12-month prevalence to lifetime prevalence, is significantly higher for respondents with irritable (40.3%) than nonirritable (28.8%) MDD (χ21=9.0, P=0.004).

Table 2 Onset and course of irritable and nonirritable DSM-IV/CIDI MDD
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Figure 1
figure 1

Age of onset for major depressive episode (MDE).

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Symptom profiles and episode severity

Tetrachoric factor analysis of the nine DSM-IV Criterion A symptoms of MDD and irritability among NCS-R respondents who endorsed a CIDI diagnostic stem question for lifetime major depression (that is, a period lasting 2 weeks or longer when the respondent experienced either sad mood most of the day nearly every day or loss of interest) was carried out. A strong first principal factor (with a 0.85 cumulative proportion of eigenvalues compared to 0.20 for the second unrotated principal factor) was found in which the factor loading for irritability (0.31) is in the lower end of the interquartile range (IQR: 25th–75th percentile) of the factor loadings of the DSM-IV symptoms (IQR: 0.30–0.54). (More detailed results available on request.)

Symptom profiles for the nine DSM-IV Criterion A symptoms in the worst lifetime episode are quite comparable for irritable and nonirritable MDD (Table 3). Significant differences are limited to fatigue and self-reproach, both of which are significantly more prevalent in irritable than nonirritable MDD. Irritable cases were also marginally more likely than nonirritable cases to report morbid thoughts of death (71.5 vs 65.5%, χ21=3.6, P=0.06). More detailed analyses (results available on request) showed that these differences were not due to differences in comorbid DSM-IV/CIDI anxiety, impulse-control or substance disorders.

Table 3 Symptom profilesa of irritable and nonirritable DSM-IV/CIDI MDE
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The distribution of clinical severity, as defined by the QIDS-SR, does not differ significantly for 12-month irritable vs nonirritable MDD (χ23=6.7, P=0.10), with 48.1% of irritable and 45.0% of nonirritable cases classified either severe or very severe (Table 4). Mean scores on the SDS also are quite similar for the two groups, although there is a consistent trend for disability to be slightly higher for irritable than nonirritable MDD (Table 5).

Table 4 Clinical severity (QIDS-SR) of 12-montha irritable and nonirritable DSM-IV/CIDI MDD
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Table 5 Role disability (Mean SDS score) of 12-montha irritable and nonirritable DSM-IV/CIDI MDE
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Sociodemographic correlates

The sociodemographic correlates of irritable MDD are generally similar to those of nonirritable MDD (Table 6). Both are significantly more common among women than men, with statistically indistinguishable female/male ORs (1.6 vs 1.9, χ21=0.6, P=0.42). Both are inversely related to income and education, although somewhat more strongly so for irritable than nonirritable cases. Both are more prevalent among the previously married than the currently married and among non-Hispanic whites than non-Hispanic blacks or Hispanics.

Table 6 Sociodemographic correlates of lifetime irritable and nonirritable DSM-IV/CIDI MDE
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There are also notable differences in the associations of irritable and nonirritable MDD with age and age-related sociodemographic variables. Irritable MDD is more prevalent than nonirritable MDD among respondents in the age range 18–44, students, the never married and respondents in the ‘other’ race-ethnic group (that is, neither non-Hispanic white, non-Hispanic black or Hispanic). Nonirritable MDD, in comparison, is more prevalent than irritable MDD among respondents ages 60+. More detailed analyses (results available on request) showed that these differences are not due to differences in comorbid DSM-IV/CIDI anxiety, impulse-control or substance disorders.

Comorbidity with other DSM-IV disorders

Lifetime comorbidity with other DSM-IV/CIDI disorders was reported by a significantly higher proportion of respondents with irritable (71.3%) than nonirritable (57.9%) MDD (F1,953=6.8, P=0.013), although ORs are consistently greater than 1.0 and generally significant for both subtypes (Table 7). The ORs of irritable MDD are higher than those of nonirritable MDD with dysthymia and seven of the nine anxiety syndromes assessed in the NCS-R. Four of the latter seven are significant at the 0.05 level. It is noteworthy that these four—GAD, panic attack, social phobia and PTSD—include the anxiety disorders with the latest AOO. The ORs of irritable MDD are also higher than those of nonirritable MDD with all three of the impulse-control disorders assessed in the core NCS-R: attention-deficit/hyperactivity disorder, oppositional-defiant disorder and IED. It is noteworthy that all these ORs are statistically significant for irritable MDD, whereas none is significant for nonirritable MDD. IED might be thought to have an especially strong association with irritability, as the uncontrollable anger attacks of IED could be seen as extreme forms of irritability. Yet only 13.7% of respondents with irritable MDD have a lifetime history of IED. Although this is considerably higher than the 5.5% lifetime prevalence of IED among respondents with nonirritable MDD, it is clear that IED is a minority phenomenon among people with irritable MDD. The ORs of irritable and nonirritable MDD with substance disorders, finally, are generally equivalent.

Table 7 Lifetime comorbidity of irritable and nonirritable DSM-IV/CIDI MDE with other DSM-IV/CIDI disorders
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Treatment

Respondents with lifetime irritable MDD who had a 12-month depressive episode were somewhat more likely than 12-month cases with nonirritable MDD to receive professional treatment for their depression within a year of the interview (64.5 vs 53.5%, z=1.9, P=0.06; Table 8). This difference was especially pronounced among those whose 12-month depression was associated with a very severe QIDS-SR score (84.5 vs 51.4%, z=3.6, P<0.001). A significantly higher proportion of irritable than nonirritable cases were also treated by a psychiatrist, although this difference was confined to very severe cases (84.5 vs 43.8%, z=4.4, P<0.001).

Table 8 Treatment of 12-montha irritable and nonirritable DSM-IV/CIDI MDE by clinical severity and sector of treatment
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Discussion

The results reported here are limited by the fact that the NCS-R used a fully structured lay-administered diagnostic interview rather than a semistructured clinician-administered diagnostic interview. However, the fact that good concordance was found between CIDI diagnoses with blinded SCID clinical diagnoses reduces this concern. In addition, irritability was defined as being ‘irritable, grouchy or in a bad mood,’ and this definition may be overinclusive. Another limitation is that irritability was assessed with only a single question for a single worst lifetime episode, possibly leading to more imprecision in the distinction between irritable and nonirritable cases than if the assessment had been made using a more detailed assessment across a number of episodes. The base rate of ‘irritability’ was not assessed in the entire sample, making it impossible to determine whether the high prevalence of irritability in MDD is different from the lifetime prevalence of irritability in the general population. However, the fact that irritability was found to have a significant factor loading with the symptoms of MDE among respondents who endorsed a lifetime history of either dysphoria or anhedonia shows that irritability is associated with the symptoms of DSM-IV major depression. This finding is consistent with clinical evidence that irritability is more common among depressed vs nondepressed subjects.23

The above limitations are likely to lead to the results regarding differences between irritable and nonirritable cases being conservative. An additional limitation, though, might have more complex effects: that respondents were not followed over time or assessed for a family history of BP disorder, raising the possibility that at least some of the respondents classified as having irritable MDD might actually be in the BP spectrum and might eventually convert to having BP disorder. On the basis of this limitation, the claim that the cases of irritable MDD seen here are non-BP should be seen as provisional.

A final noteworthy limitation is that the analysis was carried out exclusively among respondents who met DSM-IV criteria for major depression. This means that respondents with irritable depression were required to have six symptoms compared to five for respondents with nonirritable depression. It could be argued that not allowing irritability to be an alternative to sadness or lack of interest might have introduced a systematic bias toward a relatively more severe form of depression in our analysis. As noted above, though, only 28 additional cases would be classified as having irritable depression if we allowed irritability to be a diagnostic symptom of MDD. This means that any bias introduced in our analysis by requiring respondents with irritable depression to have at least six symptoms would likely be modest. This suspicion was confirmed by replicating all analyses reported above with these 28 respondents added to those considered to have irritable depression. The results were essentially unchanged (results available upon request). The only difference was that the rate of comorbid PTSD in irritable depression (16.6%) was no longer significantly higher than in nonirritable depression (11.3%).

Within the context of the above limitations, our results provide the first nationally representative US general population prevalence estimates of irritable vs nonirritable MDD. Irritability was found in roughly half the cases of MDD, making it at least as common as a number of the DSM-IV Criterion A symptoms of MDD, including all the reverse vegetative symptoms combined (weight gain, hypersomnia, psychomotor agitation) and psychomotor retardation. This finding is consistent with previous evidence that irritability is more common among depressed than nondepressed subjects.23 The prevalence of irritability found here is somewhat higher than the 37–40% irritability prevalence estimates reported in previous studies of depressed outpatients.4, 5 Recall, though, that these clinical studies considered only symptoms in the current episode whereas we considered symptoms in the worst lifetime episode. In addition, there was no consistency in any of these studies in the methods used to assess irritability.

We excluded respondents with a lifetime history of BP disorder as well as those with a history of either subthreshold BP disorder24 or core hypomanic symptoms (that is, a distinct period of abnormally and persistently elevated, expansive or irritable mood lasting several days or longer with at least one other symptom of hypomania) in recognition of the fact that depression with anger has been conceptualized by some commentators as a BP spectrum disorder.25 As noted above, the fact that many of the NCS-R respondents are still in the age of risk of onset of BP disorder means that some unknown number of those with irritable MDD might have their diagnoses changed to BP disorder in the future. However, given the very high prevalence of irritability among respondents with lifetime MDD after excluding respondents in the BP spectrum, and taking into consideration that upper-bound estimates put lifetime prevalence of BP spectrum disorder at no more than 5–7% of the population,26, 27 it is very likely that this sort of conversion will occur to a high proportion of the NCS-R respondents classified as having irritable MDD.

On the basis of the above considerations, our findings challenge the view that irritability in depression is a specific indicator of bipolarity.28, 29 The findings also raise the question whether the revised DSM and International Classification of Diseases (ICD) criteria should include irritability as a symptom of non-BP depression. Not only did we find that irritability is a common feature of non-BP depression, but we also found that irritability was meaningfully related to a number of significant clinical features. Mean retrospectively reported AOO of MDD is significantly earlier for irritable than nonirritable MDD. Although the shape of the AOO distribution is nonetheless generally consistent for the two subtypes, the earlier onset of irritable than nonirritable MDD is consistent with the one, small clinical study of which we are aware that examined this issue.30 It is unlikely that this is due to differential recall bias, as post hoc analysis shows that the same finding holds when we compare AOO of irritable and nonirritable MDD in subsamples that are matched on age at interview. It is noteworthy, though, that it has long been known that early AOO of MDE is also often found in BP disorder,31 again raising a question about the possibility that some cases of irritable MDD are in the BP spectrum.

Another important clinical finding is the significantly greater persistence of irritable than nonirritable MDD, as defined by the proportion of lifetime cases who had a 12-month depressive episode. We are aware of no prior study that has examined this issue. As noted above, the greater persistence of irritable than nonirritable MDD was still present after we controlled for lifetime comorbidity. We also adjusted for differences in AOO, as irritable MDD had an earlier onset than nonirritable MDD, which might explain the more persistent course of irritable MDD, but we found that the significantly higher 12-month/lifetime prevalence ratio of irritable than nonirritable MDD persisted when this control was introduced along with controls for comorbidity. However, retrospectively reported mean number of years with any lifetime episode did not differ significantly for irritable and nonirritable MDD, demonstrating inconsistency in the finding regarding persistence depending on the indicator used to define persistence. As course of illness is a critical clinical feature, more definitive data are needed on differences between irritable and nonirritable MDD in this regard, ideally from prospective studies.

The NCS-R finding that irritability is more prevalent in MDD among respondents in the age range 18–44 and among students is consistent with the finding of a decreasing prevalence of irritability in MDD with age in the STAR*D clinical sample.4 It is conceivable that the comparatively early AOO and young age at interview of respondents with irritable MDE are related to the fact that irritability is such a commonly occurring symptom in child and adolescent depression.1, 2 Another possibility is that irritability is becoming a more common feature of depressive episodes in recent cohorts.

The finding that severity of illness, as indicated by the QIDS-SR and the SDS, did not differ between irritable and nonirritable MDD diverges from the STAR*D finding that patients with irritable MDD had greater illness severity than those with nonirritable MDD.4 This discrepancy may be due, at least in part, to our finding that people with very severe, irritable MDD were significantly more likely to obtain psychiatric treatment than people with very severe, nonirritable MDD, leading to an overrepresentation of very severe cases of irritable MDD in specialty treatment samples.

NCS-R respondents with irritable MDD reported a higher prevalence of fatigue, self-reproach and morbid thoughts of death than those with nonirritable MDD. The elevated prevalence of morbid thoughts of death is indirectly consistent with the association between past history of suicide attempts and irritable MDD in the STAR*D study.4 The elevated prevalence of self-reproach in NCS-R irritable MDD might be part of the pattern, as self-reproach has been linked to suicidal ideation.32 It is noteworthy that similar symptom differences were found in the STAR*D sample, but these differences were explained by overall illness severity.4 It is striking that this is not the case in the NCS-R, as these symptom differences were found despite irritable and nonirritable MDD not differing in overall illness severity. This suggests that symptoms of self-reproach and morbid thoughts of death, and possibly fatigue (which was not elevated among STAR*R patients with irritable MDD) provide some genuine differentiation between irritable and nonirritable MDD. Clearly, though, these differences need to be examined in independent samples controlling for overall illness severity before we can conclude that they are due to more than idiosyncratic features of a single study.

The significantly higher prevalence of comorbid anxiety disorders among people with irritable than nonirritable MDD is in agreement with the observation that outpatients with MDD with anxious depression in the STAR*D study were significantly more likely to report irritability than those without anxious features.33 As no previous study investigated comorbidity of irritable vs nonirritable MDD with impulse-control disorders, our finding that impulse-control disorders are comorbid only with irritable MDD is unique. This is potentially important as it is the most dramatic difference we found in the clinical correlates of irritable vs nonirritable MDD. The association of irritable MDD with impulse-control disorders might account for the thus far unexplored finding in the Epidemiologic Catchment Area Survey that depression was related to violent behavior.34

The findings that irritability is a common symptom of MDD and that irritable MDD is associated with distinctive clinical features raises the possibility that the presence of irritability might be a useful MDD subtyping distinction. Whether this turns out to be the case, though, will require further investigation of differential risk factors, family aggregation and treatment response. A more detailed investigation of family aggregation of comorbid impulse-control disorders might turn out to be especially illuminating in this regard in light of the unique comorbidity of irritable MDD with impulse-control disorders.

Finally, the association in MDD of irritability with specific symptom clusters and comorbidities may reflect a psychopathological endophenotype that might defy the current DSM-IV nosology and, in fact, cut across DSM-IV clinical entities such as mood and anxiety disorders. A related example of such a cross-cutting distinction exists in the reduction in serotonergic neurotransmission, as suggested by blunted prolactin responses to fenfluramine challenges, reported in patients with both unipolar and BP depression,35 anxiety disorders such as PTSD36 and personality disorder patients with impulsive aggression.37 Consistent with these observations, we have found that patients with MDD, irritability and anger attacks had a significantly greater blunting of the prolactin response to fenfluramine challenge than patients with MDD without irritability and anger attacks.38 One could hypothesize that this particular endophenotype may share signs of serotonergic dysregulation, in addition to the clinical characteristics that we have identified, although further studies would need to be carried out to assess the specificity and temporal stability of this possible subtype.

With regard to differential treatment response, no study has ever investigated whether irritability is a moderator of antidepressant treatment response. However, the fact that patients with MDD with irritability and anger attacks have been shown to have distinctive neurobiological features, such as blunting of the prolactin response to fenfluramine challenge,38 and a distinctive pattern of regional cerebral blood flow in the left ventromedial prefrontal cortex and left amygdala during anger induction39 raises the possibility that there might be distinctive responsiveness to antidepressant treatment. This is an issue that clearly warrants additional investigation in light of the results presented in the current report.

Even before further studies of risk factors and consequences are carried out, though, the results reported here raise the question whether irritability should be included as a symptom of MDD in the revised DSM-V and ICD-11 diagnostic systems. We saw that irritability is as strongly related as other DSM-IV symptoms with the underlying dimension of depression symptomatology in factor analysis. We saw that the prevalence of irritable MDD would be increased by roughly one-fifth (from 5.3 to 6.4% lifetime prevalence), but not dramatically, by including irritability as a core Criterion A symptom of MDD. Thorough evaluation of the extent to which these additional cases would have similar treatment response and correlates to cases that meet current DSM-IV criteria for irritable MDD is beyond the scope of this report. However, the apparent importance of irritability in MDD documented here suggests that clinical studies are needed of the people who would be conferred a diagnosis of MDD if irritability were added as a core symptom in DSM-V and ICD-11.

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Acknowledgements

The National Comorbidity Survey Replication (NCS-R) was supported by the National Institute of Mental Health (NIMH; U01-MH60220) with supplemental support from the National Institute of Drug Abuse, the Substance Abuse and Mental Health Services Administration, the Robert Wood Johnson Foundation (Grant No. 044780) and the John W Alden Trust. Collaborating NCS-R investigators include Ronald C Kessler (Principal Investigator, Harvard Medical School), Kathleen Merikangas (Co-principal Investigator, NIMH), James Anthony (Michigan State University), William Eaton (The Johns Hopkins University), Meyer Glantz (NIDA), Doreen Koretz (Harvard University), Jane McLeod (Indiana University), Mark Olfson (Columbia University College of Physicians and Surgeons), Harold Pincus (University of Pittsburgh), Greg Simon (Group Health Cooperative), T Bedirhan Ustun (World Health Organization), Michael Von Korff (Group Health Cooperative), Philip Wang (Harvard Medical School), Kenneth Wells (UCLA), Elaine Wethington (Cornell University) and Hans-Ulrich Wittchen (Max Planck Institute of Psychiatry). The views and opinions expressed in this report are those of the authors and should not be construed to represent the views of any of the sponsoring organizations, agencies or US Government. A complete list of NCS publications and the full text of all NCS-R instruments can be found at http://www.hcp.med.harvard.edu/ncs. Send correspondence to NCS@hcp.med.harvard.edu. The NCS-R is carried out in conjunction with the World Health Organization World Mental Health (WMH) Survey Initiative. We thank the staff of the WMH Data Collection and Data Analysis Coordination Centers for assistance with instrumentation, fieldwork and consultation on data analysis. These activities were supported by the John D and Catherine T MacArthur Foundation, the Pfizer Foundation, the US Public Health Service (R13MH066849, R01-MH069864 and R01 DA016558), Eli Lilly and Company, GlaxoSmithKline, Ortho-McNeil Pharmaceutical Inc. and the Pan American Health Organization. A complete list of WMH publications and instruments can be found at (http://www.hcp.med.harvard.edu/wmhcidi).

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Affiliations

  1. Department of Psychiatry, Massachusetts General Hospital, Boston, MA, USA

    M Fava

  2. Department of Health Care Policy, Harvard Medical School, Boston, MA, USA

    I Hwang, N Sampson, E E Walters & R C Kessler

  3. Department of Psychiatry, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA

    A J Rush

  4. Department of Clinical Sciences, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA

    A J Rush

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  1. M Fava
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  2. I Hwang
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  3. A J Rush
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  4. N Sampson
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  5. E E Walters
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  6. R C Kessler
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Correspondence to R C Kessler.

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Financial Disclosures

Dr Fava has research support from Abbott Laboratories, Alkermes, Aspect Medical Systems, AstraZeneca, Bristol-Myers Squibb Company, Cephalon, Eli Lilly and Company, Forest Pharmaceuticals Inc., GlaxoSmithKline, Johnson & Johnson Pharmaceuticals, Lichtwer Pharma GmbH, Lorex Pharmaceuticals, Novartis, Organon Inc., PamLab LLC, Pfizer Inc., Pharmavite, Roche, Sanofi-Synthelabo, Solvay Pharmaceuticals Inc. and Wyeth-Ayerst Laboratories. He has served as an advisor/consultant for Aspect Medical Systems, AstraZeneca, Bayer AG, Biovail Pharmaceuticals Inc., BrainCells Inc., Bristol-Myers Squibb Company, Cephalon, Comellas, Cypress Pharmaceuticals, DOV Pharmaceuticals, Eli Lilly and Company, EPIX Pharmaceuticals, Fabre-Kramer Pharmaceuticals Inc., Forest Pharmaceuticals Inc., GlaxoSmithKline, Grunenthal GmbH, Janssen Pharmaceutica, Jazz Pharmaceuticals Inc., Johnson & Johnson Pharmaceuticals, Knoll Pharmacuetical Company, Lundbeck, MedAvante Inc., Merck, Neuronetics, Novartis, Nutrition 21, Organon Inc., PamLab LLC, Pfizer Inc., PharmaStar, Pharmavite, Roche, Sanofi-Synthelabo, Sepracor, Solvay Pharmaceuticals Inc., Somaxon, Somerset Pharmaceuticals and Wyeth-Ayerst Laboratories. He has been on speaker bureaus for AstraZeneca, Boehringer Ingelheim, Bristol-Myers Squibb Company, Cephalon, Eli Lilly and Company, Forest Pharmaceuticals Inc., GlaxoSmithKline, Novartis, Organon Inc., Pfizer Inc., PharmaStar and Wyeth-Ayerst Laboratories. He holds equity in Compellis and MedAvante. Dr Kessler has been a consultant for GlaxoSmithKline Inc., Pfizer Inc., Wyeth-Ayerst, Sanofi-Aventis, Kaiser Permanente and Shire Pharmaceuticals; has served on advisory boards for Eli Lilly and Company and Wyeth-Ayerst; and has had research support for his epidemiological studies from Bristol-Myers Squibb, Eli Lilly and Company, GlaxoSmithKline, Johnson & Johnson Pharmaceuticals, Ortho-McNeil Pharmaceuticals Inc., Pfizer Inc. and Sanofi-Aventis. Dr Rush has provided scientific consultation to or served on Advisory Boards for Advanced Neuromodulation Systems Inc., AstraZeneca, Best Practice Project Management Inc., Bristol-Myers Squibb Company/Otsuka, Cyberonics Inc., Forest Pharmaceuticals, GlaxoSmithKline, Jazz Pharmaceuticals, Eli Lilly and Company, Magellan Health Services, Merck & Co. Inc., Neuronetics, Novartis, Ono Pharmaceutical, Organon Inc., Pamlab Pfizer Inc. and Transcept Pharmaceuticals. He has received royalties from Guilford Press and Healthcare Technology Systems and research/grant support from the National Institute of Mental Health and the Stanley Medical Research Institute; has been on speaker bureaus for Cyberonics Inc., Forest Pharmaceuticals Inc. and GlaxoSmithKline; and owned stock in Pfizer Inc.

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Fava, M., Hwang, I., Rush, A. et al. The importance of irritability as a symptom of major depressive disorder: results from the National Comorbidity Survey Replication. Mol Psychiatry 15, 856–867 (2010). https://doi.org/10.1038/mp.2009.20

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Keywords

  • epidemiology
  • irritability
  • major depressive disorder
  • National Comorbidity Survey Replication
  • adult

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