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ORIGINAL ARTICLE
Internalizing and externalizing behavior in adult ADHD
Christian Jacob • Silke Gross-Lesch •
Thomas Jans • Julia Geissler • Andreas Reif •
Astrid Dempfle • Klaus-Peter Lesch
Received: 8 February 2013 / Accepted: 11 February 2014
� Springer-Verlag Wien 2014
Abstract Although there are many studies available
investigating internalizing and externalizing behavior in
childhood and adolescent manifestations of attention-defi-
cit/hyperactivity disorder, there is limited information
about their relevance in adults featuring persistence of the
disease. We examined a large sample of 910 adults affected
with attention-deficit/hyperactivity disorders (AADHD) for
internalizing and externalizing behavior. Regarding corre-
lates of internalizing behavior, AADHD probands showed
significantly higher scores of the anxiety- and depression-
related personality traits Neuroticism and Harm Avoid-
ance, compared with reference values. The lifetime
comorbidity of depressive disorders, anxiety disorders, and
anxious or fearful Cluster C personality disorders (PDs) is
elevated in AADHD patients compared with general pop-
ulation. Regarding correlates of externalizing behavior,
patients affected with AADHD show significantly lower
scores of Conscientiousness and significantly higher scores
of Novelty Seeking than the published German reference
values. Emotional, dramatic, or erratic Cluster B PDs were
most frequent in AADHD. Internalizing and externalizing
behavior notably affected psychosocial status to a similar
extent. The frequency of both internalizing and external-
izing behavior in AADHD might reflect an underlying
emotional regulation disorder.
Keywords AADHD � Internalizing behavior �Externalizing behavior
Introduction
A well-known concept in the field of child psychology and
psychiatry is the distinction between internalizing and
externalizing behavior that was primarily developed by
Achenbach (1966). Internalizing behavior such as anxious/
depressive symptoms, social withdrawal, somatic com-
plaints, and traumatic stress affects internal psychological
environment rather than the external world (Liu 2003).
There is general consensus that episodes of depression and
anxiety disorders are classified as internalizing behavior.
Somatoform disorders, eating disorders, and tic disorders
are discussed as belonging to this category.
Externalizing behavior refers to a group of behavioral
problems that manifest in outward behavior, thereby
focusing on the negative impact on the environment (Liu
2003). Externalizing behavior consists of disruptive,
hyperactive, and aggressive behaviors (Hinshaw 1987).
The differentiation between externalizing and antisocial
behavior is under discussion (Liu 2003) as some
researchers view externalizing behavior to represent a less
severe form of antisocial behavior, especially in young
children (Shaw and Winslow 1997). Attention-deficit/
hyperactivity disorders (ADHD) of the combined and
Astrid Dempfle and Klaus-Peter Lesch have contributed equally to
this work.
C. Jacob (&) � S. Gross-Lesch � A. Reif � K.-P. Lesch
Department of Psychiatry, Psychosomatics and Psychotherapy,
University of Wuerzburg, Fuechsleinstr. 15, 97080 Wurzburg,
Germany
e-mail: [email protected]; [email protected]
T. Jans � J. Geissler
Department of Child and Adolescent Psychiatry,
Psychosomatics and Psychotherapy, University Hospital
Wuerzburg, Fuechsleinstr. 15, 97080 Wurzburg, Germany
A. Dempfle
Institute of Medical Biometry and Epidemiology,
Philipps-University Marburg, Bunsenstrasse 3,
35037 Marburg, Germany
123
ADHD Atten Def Hyp Disord
DOI 10.1007/s12402-014-0128-z
hyperactive/impulsive subtypes can be classified as exter-
nalizing behavior (Liu 2003).
There is evidence that parental internalizing problems
are associated with child psychosocial problems (Spijkers
et al. 2013). Children with externalizing behavior problems
such as conduct disorder are more likely to grow up to
become delinquent as adolescents, and criminal and violent
as adults (Farrington 1997). Externalization behavior is
among the most frequent features of incarcerated male
adolescents and male young adults (Rosler et al. 2004).
Currently, the concept of internalizing and externalizing
behavior has rarely been adopted in adult psychiatry.
Accordingly, there are no modifications of the conceptu-
alization and categorization of internalizing and external-
izing behavior that refer to adults. Youth Self-Report and
the Young Adult Self-Report (YSR, YASR) are valid for
diagnosing externalizing and internalizing disorders in
children, adolescents, and young adults (Achenbach 1991,
1997). There are no standardized assessment scales for
adults.
Internalizing and externalizing behavior in children and
adolescents affected with ADHD is subject of multiple
studies (Connor and Ford 2012). Studies including adults
affected with ADHD (AADHD), however, do not focus or
even name these phenomena irrespective of multiple
studies for the association with personality traits and the
comorbidity of adult ADHD with axis I and axis II (per-
sonality) disorders (Jacob et al. 2007).
Neuroticism (revised NEO personality inventory, NEO-
PI-R, Costa and McCrae 1992) and Harm Avoidance
(Tridimensional Personality Questionnaire, TPQ, Clonin-
ger et al. 1993) are anxiety- and depression-associated
personality traits that might reflect internalizing behavior
(Griffith et al. 2010).
Adults affected with AADHD have significantly higher
levels of the anxiety- and depression-associated personality
traits Neuroticism according to NEO-PI-R (Ranseen et al.
1998; Retz et al. 2004; Jacob et al. 2007) and Harm
Avoidance (TPQ) (Downey et al. 1996, 1997; Jacob et al.
2007).
Low scores on Agreeableness (NEO-PI-R) and Consci-
entiousness (NEO-PI-R) that are related to antisocial and
criminal behavior (Ross et al. 2009) might reflect exter-
nalizing behavior. The published studies are in line with
the notion that individuals affected with AADHD score
significantly lower in Conscientiousness than in controls
(Costa and McCrae 1992; Ranseen et al. 1998; Retz et al.
2004; Sobanski 2006). Novelty Seeking (TPQ) is associ-
ated with exploratory activity in response to novel stimu-
lation, impulsive decision making, extravagance in
approach to reward cues, and quick loss of temper and
avoidance of frustration (Cloninger et al. 1993). Signifi-
cantly higher scores of Novelty Seeking (TPQ) in adult
ADHD are replicated (Downey et al. 1996, 1997; Jacob
et al. 2007).
According to the National Comorbidity Survey Repli-
cation (NCS-R), 18.6 % of subjects with AADHD have a
12-month comorbidity of depressive episodes (Kessler
et al. 2006). The 12-month comorbidity of anxiety disor-
ders is 47.1 % in the subjects affected with AADHD
according to the NCS-R (Kessler et al. 2006). Social
phobia has the highest 12-month comorbidity (29.3 %)
among the specific anxiety disorders in AADHD according
to NCS-R (Kessler et al. 2006).
Since personality disorders (PDs) have, due to the age of
onset, a much higher relevance in adults than in adoles-
cences, no one raised the question which PDs are related to
internalizing and externalizing behavior. Anxious or fearful
Cluster C PDs (avoidant, dependent, and obsessive com-
pulsive PD) share symptoms and affection of internal
psychological environment with other disorders that are
classified as internalizing behavior (Liu 2003). In the
Epidemiologic Survey on Alcohol and Related Conditions
(NESARC), the third most common PD is Cluster C
obsessive–compulsive PD with 19.3 % (GP = 7.8 %)
(Bernardi et al. 2012). There is multiple evidence from
clinical studies that Cluster C PDs are more frequent than
emotional, dramatic, or erratic Cluster B PDs in AADHD
(Matthies et al. 2011; Miller et al. 2007; Williams et al.
2010). Emotional, dramatic, or erratic Cluster B PDs share
outward behavior that may have a negative impact on the
environment with other externalizing behavior (Liu 2003).
In the NESARC, the most frequent PDs in AADHD are
Cluster B borderline PD with 33.7 % (GP = 5.2 %) and
Cluster B narcissistic PD with 25.2 % (GP = 5.7 %)
(Bernardi et al. 2012).
In general, there is considerable evidence that parent and
adolescent internalizing behavior is associated with more
impaired functioning at various levels of the family system
(Hughes and Gullone 2008).
The aim of this study was to examine whether inter-
nalizing and externalizing behavior occurred more often in
AADHD, whether subtypes differed in this respect, and
whether they impacted on psychosocial status. Therefore,
we tested several hypotheses: (1) whether AADHD in
general and inattentive type AADHD in particular are
associated with higher scores of the anxiety- and depres-
sion-related personality traits Neuroticism (NEO-PI-R) and
Harm Avoidance (TPQ). (2) Whether people affected with
AADHD in general and inattentive type AADHD in par-
ticular have a high comorbidity with depression, anxiety
disorders, and anxious or fearful Cluster C PDs. (3) Whe-
ther patients affected with AADHD in general and with
combined and hyperactive type AADHD in particular have
lower scores in Agreeableness (TPQ) and Conscientious-
ness (NEO-PI-R) and higher scores in Novelty Seeking
C. Jacob et al.
123
(TPQ). (4) Whether these patients have higher comorbidity
with emotional, dramatic, or erratic Cluster B PDs. (5) And
whether both internalizing and externalizing behaviors
result in lower psychosocial status in AADHD.
Methods
Participants
In- and outpatients affected with AADHD that referred to
the Department of Psychiatry, Psychosomatics, and Psy-
chotherapy, University of Wuerzburg were recruited
between 2003 and 2009. The first 372 patients (173
females, 199 males; mean age 33.3 years, SD 10.3) were
recruited 2003–2005 (Jacob et al. 2007). The extended
sample comprises 910 patients (452 females, 458 males;
mean age 34.5 years, SD = 10.2); the second wave was
recruited 2006–2011 in an identical fashion.
Inclusion criteria were AADHD according to the diag-
nostic criteria of DSM-IV, onset before the age of 7 years
via retrospective diagnosis, life-long persistence, and cur-
rent diagnosis (Jacob et al. 2008). Age at recruitment was
between 18 and 65 years. Probands affected with substance
use disorders underwent detoxification in an inpatient set-
ting. Exclusion criteria were as follows: the symptoms
occur exclusively during the course of a pervasive devel-
opmental disorder, schizophrenia, or other psychotic dis-
order or symptoms are better accounted for by another
mental disorder (criterion E of DSM-IV). Further exclusion
criteria were as follows: IQ level below 80 (Mehrfachwahl-
Wortschatz-Intelligenztest, MWT-B \13 points) (Lehrl
1977) and bipolar affective disorder (excluded due to the
unsolved problems of differential diagnosis). Inclusion and
exclusion criteria are not modified compared with our
previously published protocol (Jacob et al. 2007).
The Ethics Committee of the University of Wuerzburg
approved the study, and written informed consent was
obtained from all patients after procedures and aims of the
study had been fully explained.
Measures
Diagnosis of AADHD was made as a four-step procedure
(Jacob et al. 2008). First, other physical and mental condi-
tions were excluded that could explain the symptoms more
adequately. Mental disorders were assessed with the struc-
tured clinical interview of axis I and axis II (SCID I/II) to
exclude differential diagnoses and to detect comorbid con-
ditions (Wittchen et al. 1997). The intellectual functioning
was assessed with MWT-B (AADHD: IQ mean = 111.5,
SD = 14.0) to exclude patients with mild cognitive
impairment. Second, AADHD was assessed according to the
Diagnostic and Statistical Manual of Mental Disorders, 4th
Edition (DSM-IV) criteria. Informative input from partners,
relatives, and friends was also collected. To ensure diag-
nostic validity, subjects were examined by more than one
experienced investigator at least at two time points. In the
case of a mismatch of the results, the patient was again
examined. Third, diagnosis of childhood manifestation of
ADHD was retrospectively assessed in a structured clinical
interview. Wender Utah Rating Scale was performed
(Wender 1995). Additional information from school report
cards/certificates and from parents was included if available,
but were not obligatory. Fourth, anamnestic information
demonstrates that the symptoms are a lifelong condition and
definitely do not have an episodic course.
Internalizing and externalizing behavior was assessed
by two different personality trait questionnaires (NEO-PI-R
and TPQ) the structured clinical interviews of axis I
(Structured Clinical Interview for DSM-IV Axis I Disorders
[SCID I]; First et al. 1996) and axis II (Structured Clinical
Interview for DSM-IV Axis II PDs [SCID II]; First et al.
1997) disorders.
NEO-PI-R is designed to give measures of the five
domains of personality according to the personality model
of Costa and McCrae (1992). TPQ follows a biological
model of personality traits derived from animal research
that was proposed by Cloninger et al. (1993).
Internalizing behavior is assessed by the anxiety- and
depression-related personality traits Neuroticism (NEO-PI-
R) and Harm Avoidance (TPQ). Higher scores for both
personality traits indicate more internalizing behavior. The
latter is heritable and related to high serotonergic activity
(Cloninger et al. 1993). Along the concept that PDs reflect
the extreme ends of normally distributed personality traits
(Reif and Lesch 2003), anxious–fearful Cluster C PDs
(avoidant, dependent, obsessive–compulsive, passive-
aggressive, and depressive PD) were also classified as
internalizing behavior. Finally, we classified mood and
anxiety disorders as internalizing behavior, but excluded
somatoform disorders, eating disorders, and tic disorders,
because there is no general consensus for their classifica-
tion as internalizing behavior.
Low scores on Agreeableness (NEO-PI-R) and Consci-
entiousness (NEO-PI-R), high scores on Novelty Seeking
(TPQ), and comorbidity with emotional, dramatic, or
erratic Cluster B PDs (antisocial, borderline, histrionic, and
narcissistic PDs) are used to detect externalizing behavior.
The concept of Novelty Seeking (TPQ) assumes a dopa-
minergic dysregulation (Cloninger et al. 1993).
Psychosocial status
Psychosocial status was assessed on the basis of a stan-
dardized biographical history of each patient (Jacob et al.
Internalizing and externalizing behavior
123
2007). The following conditions were rated with one point
each (which were simply summarized to obtain the total
score): family status (1 point max.): divorced, or separated,
or two or more times married. Education (2 points max.):
discontinued, two or more classes repeated. Occupational
qualification (2 points max.): unskilled, unemployed.
Additional factors were psychiatric inpatient treatment,
delinquency, suicidal behavior, and aggressive behavior
(one point each). This results in a psychosocial status scale
(with values 0–9), where low scores indicate fewer psy-
chosocial problems and thus a better psychosocial status (in
our sample: mean 4.0, SD 1.0).
Statistical analysis
Frequencies of comorbid axis I and axis II disorders were
calculated for the entire AADHD sample and separately for
AADHD subtypes. Personality traits were compared with
published German reference values (Ostendorf and Ang-
leitner 2004; Weyers et al. 1998) by standardizing each
patient’s score with the appropriate age-, group-, and sex-
specific population mean and standard deviation and
comparing the resulting standardized scores to zero by the
sign test. Differences in personality traits (as measured by
NEO-PI-R and TPQ values) between groups (e.g., sub-
types) were tested by ANOVA. Prevalence of axis I or II
disorders (both specific PDs and ‘‘any Cluster B’’ or ‘‘any
Cluster C’’ PDs) was compared between all three subtypes
by chi-square test. The relationship between psychosocial
status and personality traits, PDs, or axis 1 disorders was
investigated by a linear regression model, adjusted for age
and ADHD subtype. All reported p values are nominal,
uncorrected, and should be evaluated against appropriate
levels of significance to account for multiple testing of
several hypotheses.
Results
Internalizing behavior
AADHD subjects showed significantly higher anxiety- and
depression-related personality traits Neuroticism (NEO-PI-R,
p \ 0.00001) and Harm Avoidance (TPQ, p \ 0.00001)
scores than the published German reference values (Ostendorf
and Angleitner 2004; Weyers et al. 1998, Table 1). Neuroti-
cism and Harm Avoidance scores were significantly different
between AADHD subtypes (both p \ 0.0001), but patients
affected with inattentive type AADHD were intermediate in
Neuroticism and only very slightly higher in Harm Avoidance
than in patients affected with AADHD of the combined or
hyperactive/impulsive type. We did not perform subscale
analyses of Neuroticism (anxiety, angry hostility, depression,
self-consciousness, impulsivity, and vulnerability) due to the
lack of validity.
The lifetime comorbidity of depressive disorders and
anxiety disorders is increased in AADHD compared with the
general population (Wittchen et al. 2010; Table 2). Differ-
ences in comorbidity with depressive and anxiety disorders
between AADHD subtypes were mostly not significant.
Patients affected with AADHD of the inattentive type had a
similar prevalence of depressive disorders as those with
combined type (and higher than hyperactive/impulsive
type). The prevalence of anxiety disorders was similar in
patients with AADHD of the inattentive type and the
hyperactive/impulsive type (and lower than combined type).
The prevalence of (internalizing) Cluster C PDs is much
higher in AADHD patients than in the general population
(Table 2). Avoidant Cluster C PD is the third most pre-
valent PD in AADHD. For most Cluster C PDs, differences
between subtypes were highly significant. However, only
patients affected with AADHD of the hyperactive/impul-
sive type had much lower comorbidity with Cluster C PDs,
while those with combined and inattentive type AADHD
had a very similar comorbidity with Cluster C PDs.
Externalizing behavior
People affected with AADHD show significantly lower
scores of Conscientiousness (NEO-PI-R, p \ 0.00001) and
significantly higher scores of Novelty Seeking (TPQ,
p \ 0.00001) than the published German reference values
(Ostendorf and Angleitner 2004; Weyers et al. 1998,
Table 3), while there are no relevant differences in
Agreeableness (NEO-PI-R, p = 0.89) between those two
groups. Patients affected with combined and hyperactive
type AADHD have lower scores in Agreeableness (TPQ),
while the hypothesized differences in Conscientiousness
(NEO-PI-R) and Novelty Seeking (TPQ) could not be
detected. Scores in Agreeableness (TPQ), Conscientious-
ness (NEO-PI-R), and Novelty Seeking (TPQ) were sig-
nificantly different between AADHD subtypes, but patients
affected with inattentive type AADHD were intermediate
in Conscientiousness and Novelty Seeking and only very
slightly higher in Agreeableness than in patients affected
with AADHD of the combined or hyperactive/impulsive
type.
The prevalence of (externalizing) Cluster B PDs is also
much higher in AADHD patients than in the general pop-
ulation (Table 4). The most prevalent PDs in patients
affected with AADHD were narcissistic PD followed by
histrionic PD (Table 3). In comparison, the comorbidity
with antisocial PD was relatively infrequent. Combined
and hyperactive type AADHD patients had higher comor-
bidity with Cluster B PDs (with exception of borderline
PD) than inattentive type AADHD patients.
C. Jacob et al.
123
Co-occurrence of internalizing and externalizing
behavior
Remarkably, many AADHD patients show both internal-
izing and externalizing behavior. Only 249 patients
(28.4 %) had no PD, while 275 patients (31.4 %) had
exactly one PD and 353 patients (40.3 %) had two or more
PDs. Of these, 218 patients (24.9 %) had both externalizing
Cluster B and internalizing Cluster C PDs. Even more
frequent was the co-occurrence of externalizing Cluster B
PDs with internalizing mood or anxiety disorders, which
were present in 301 patients (34.3 %).
Table 1 Personality traits and internalizing behavior
All adult
ADHD
Combined
type
Inattentive
type
Hyperactive
type
Subtype
differences
German norm
values
Adult ADHD
versus Norms
Mean SD Mean SD Mean SD Mean SD p valueb Mean SD p valuec
NEO-PI-R n = 860a n = 573 n = 222 n = 65
Neuroticism 115.6 25.8 119.7 24.4 111.5 25.4 94.1 26.8 \0.0001 91.1 23.6 \0.00001
TPQ n = 884a n = 585 n = 230 n = 66
Harm Avoidance 19.6 7.0 20.0 7.0 20.3 6.5 13.5 6.7 \0.0001 15.5 6.3 \0.00001
a Not all the included patients have completed the NEO-PI-R and TPQ questionnairesb p value for difference between subtypes (ANOVA) German norm values for NEO-PI-R according to Ostendorf and Angleitner (2004) and for
TPQ according to Weyers et al. (1998)c p value from sign test on age- and sex-standardized scores
Table 2 Axis I/II disorders and internalizing behavior
All adult
ADHD
Combined
type
Inattentive
type
Hyperactive
type
Subtype
differences
General population
prevalence (%)
n % n % n % n % p value Median (%)
Any depressive disorders 480 55 327 55.0 125 55.8 28 44.4 0.21
Major depression 362 41.8 255 44.0 90 40,2 17 27.0 0.02 5.7
Dysthymic disorder 89 10.3 59 10.2 24 10.8 6 9.5 0.96
Depression NOS 134 15.6 86 15.0 38 17.0 10 15.9 0.74
Any anxiety disorders 236 27.1 174 29.7 49 21.9 13 20.6 0.03
Panic disorder 53 6.1 46 7.9 3 1.3 4 6.3 0.001 1.2
Agoraphobia 33 3.8 27 4.6 3 1.3 3 4.8 0.06 1.2
Social phobia 98 11.3 69 11.8 25 11.2 4 6.3 0.47 2.0
Specific phobia 44 5.0 31 5.3 11 4.9 2 3.2 0.91 4.9
Obsessive compulsive disorder 16 1.8 11 1.9 5 2.2 0 0 0.71 0.7
Post-traumatic stress disorder 30 3.4 21 3.6 8 3.6 1 1.6 0.91 2.3
General anxiety disorder 33 3.8 25 4.3 6 2.7 2 3.2 0.62
Any Cluster C PD 374 42.6 257 44.2 105 45.6 12 18.2 0.0005 Median Pooled
Avoidant PD 163 18.6 108 18.6 55 23.8 0 0 0.0005 1.2 1.2
Dependent PD 32 3.6 26 4.5 6 2.6 0 0 0.13 1.3 2.2
Obsessive–compulsive PD 160 18.2 109 18.8 40 17.4 11 16.7 0.88 2.1 2.3
Passive–aggressive PD 116 13.2 90 15.5 25 10.9 1 1.5 0.002 1.7 2.6
Depressive PD 96 10.9 70 12.1 25 10.9 1 1.5 0.2
n = number of included patients affected with adult ADHD
p value for difference between subtypes (chi-square test)
Number = number of included patients affected with adult ADHD
General population axis I (Wittchen et al. 2010)
General population axis II meta-analytic findings of Torgersen et al. (2001)
IB internalizing behavior
Internalizing and externalizing behavior
123
Psychosocial status
The mean score of the psychosocial status in the whole
AADHD sample was 4.0 (SD = 1.0). We do not have data of a
healthy control group available to judge the effect of AADHD
per se. There was no relevant difference between males and
females (p = 0.7), but a small, statistically significant effect of
age (p = 0.03, with younger patients having more psychoso-
cial problems than older patients, which could plausibly be an
ascertainment effect) and AADHD subtype (p = 0.05, with
the hyperactive subtype having on average 0.25 psychosocial
problems more than the other subtypes). We therefore adjusted
all following analyses for age and subtype.
Among the disorders that can be regarded as repre-
senting externalizing behavior, the strongest effect on
psychosocial score was seen for AADHD patients with
antisocial or borderline PD, who reported on average 4.6
and 4.4 more serious problems than compared with 4.0 in
those without such a PD (Table 5). In general, AADHD
patients who had at least one Cluster B PD had worse
psychosocial status of 4.1 than patients who did not have a
Cluster B PD (mean of 3.9). Externalizing behavior as
measured by Conscientiousness scores, on the other hand,
was associated with better psychosocial status. Individuals
of the same age and subtype who differ by 44 points in
their Conscientiousness score (equivalent to 2 standard
deviations in our sample) have on average a difference of
0.26 serious problems on the psychosocial scale.
Internalizing disorders on axis 1 were associated with
worse psychosocial status: mood disorders in general
(mean psychosocial score of 4.1) and in particular major
depression (mean score of 4.1) as well as anxiety disorders
(mean score of 4.2), while those without any mood disor-
ders had a mean psychosocial score of 3.9. Among Cluster
C PDs, only passive-aggressive PD leads to significantly
worse psychosocial score (mean 4.4), while obsessive–
compulsive PD was associated with a better psychosocial
score (mean 3.8). Higher Neuroticism and Harm Avoid-
ance scores were also associated with worse psychosocial
status. A difference of 26 in Neuroticism score (again 2 SD
in our sample) is associated with 0.2 more serious psy-
chosocial problems (at identical age and subtype).
Table 3 Personality traits and externalizing behavior
All adult
ADHD
Combined
type
Inattentive
type
Hyperactive
type
Subtype
differences
German
norm values
Adult ADHD
versus Norms
Mean SD Mean SD Mean SD Mean SD p valueb Mean SD p valuec
NEO-PI-R n = 860a n = 573 n = 222 n = 65
Agreeableness 111.9 17.0 111.1 17.1 115.2 15.7 107.1 18.0 0.0005 112.6 17.0 0.89
Conscientiousness 91.1 22.0 88.6 21.3 89.9 20.5 116.3 17.8 \0.0001 113.9 20.1 \0.00001
TPQ n = 884a n = 585 n = 230 n = 66
Novelty Seeking 19.2 5.8 20.0 5.6 17.8 5.9 17.8 6.1 \0.0001 13.9 5.6 \0.00001
a Not all the included patients have completed the NEO-PI-R and TPQ questionnairesb p value for difference between subtypes (ANOVA)
German norm values for NEO-PI-R according to Ostendorf and Angleitner (2004) and for TPQ according to Weyers et al. (1998)c p value from sign test on age- and sex-standardized scores
Table 4 Personality disorders and externalizing behavior
Adult ADHD Combined type Inattentive type Hyperactive type Subtype differences General population
prevalence (%)
n % n % n % n % p value Median Pooled
Any Cluster B 451 51.4 318 54.7 97 42.2 36 54.5 0.006
Antisocial PD 55 6.3 41 7.1 9 3.9 5 7.6 0.19 0.8 1.6
Borderline PD 157 17.9 124 21.3 30 13.0 3 4.5 0.0005 1.4 1.2
Histrionic PD 196 22.3 154 26.5 30 13.0 12 18.2 0.0005 2.1 2.7
Narcissistic PD 226 25.8 155 26.7 46 20.0 25 37.9 0.004 0.2 0.9
n = number of included patients affected with adult ADHD
p value for difference between subtypes (Chi-square test)
General population = meta-analytic findings of Torgersen et al. (2001)
EB externalizing behavior, IB internalizing behavior
C. Jacob et al.
123
Discussion
Our data indicate that internalizing and externalizing
behavior is frequent and relevant not only in childhood and
adolescent manifestations of ADHD, but also in AADHD.
Due to the clinical relevance of personality traits in adults,
the assessment of internalizing behavior should include the
anxiety- and depression-related personality traits Neuroti-
cism (NEO-PI-R) and Harm Avoidance (TPQ). We confirm
earlier findings of significantly higher scores of Neuroti-
cism (NEO-PI-R) and Harm Avoidance (TPQ) in AADHD
compared with the published German reference values
(Downey et al. 1996, 1997; Jacob et al. 2007; Ranseen
et al. 1998; Retz et al. 2004). However, we have to consider
that almost all subscales of NEO-PI-R except for Agree-
ableness significantly differ in AADHD compared with
controls. Further, we confirm that internalizing behavior on
axis I such as mood and anxiety disorders is very common
in AADHD. The co-occurrence of internalizing and
externalizing disorders is common in our probands affected
with AADHD. Patients with Cluster B PDs have a high
comorbidity with mood and anxiety disorders and Cluster
C PDs. Although an average difference of 0.5 points in the
psychosocial status may seem small, in fact it is not given
the crude nature of the scale: an average difference of 0.5
could, e.g., be obtained if every second patient in the PD
group would be divorced as opposed to no divorces in the
control group.
There is a considerable debate whether PDs are distinct
disease entities or extreme variations of ‘‘normal’’ per-
sonality traits, following a Gaussian distribution (Reif and
Lesch 2003). Interestingly, AADHD subtypes did not
influence internalizing behavior in AADHD. Both inter-
nalizing and externalizing behavior is relevant from a
psychosocial point of view. Neuroticism and Harm
Avoidance as well as mood and anxiety disorders are
associated with worse psychosocial status in our sample of
adults affected with ADHD with a very similar effect size
to that of externalizing Cluster B PDs.
Comorbid emotional, dramatic, or erratic Cluster B PDs
are most frequent in our AADHD sample. The low
comorbidity with antisocial PDs in our study reflects the
recruitment in a tertiary clinical referral center. Adult
ADHD subtypes are related to Agreeableness and most of
the Cluster B PDs. Patients affected with hyperactive/
impulsive and combined type of AADHD have an elevated
comorbidity with Cluster B PDs that might reflect exter-
nalizing behavior. In particular, borderline PD and antiso-
cial PD lowered the psychosocial status. Since all items
included in this psychosocial status scale are important life
events or serious problems, we consider a mean difference
of 0.5 points as clinically relevant. Although an average
difference of 0.5 points in the psychosocial status may
seem small, in fact it is not given the crude nature of the
scale: an average difference of 0.5 could, e.g., be obtained
if every second 75 % of patients with a specific PD group
would be divorced as opposed to only 25 % of divorces in
the control group without this particular PD.
Table 5 Psychosocial status
Effect on
psychosocial
status
p value
Estimate SD
Any depressive disorder IB 0.15 0.07 0.04
Major depression IB 0.10 0.04 0.009
Dysthymic disorder IB 0.03 0.06 0.67
Depression NOS IB -0.03 0.05 0.58
Any anxiety disorder IB 0.23 0.08 0.006
Panic disorder IB 0.09 0.08 0.25
Agoraphobia IB 0.11 0.1 0.26
Social phobia IB 0.11 0.06 0.07
Specific phobia IB 0.06 0.08 0.48
Obsessive compulsive disorder IB 0.10 0.13 0.41
Post-traumatic stress disorder IB 0.05 0.1 0.62
General anxiety disorder IB 0.03 0.09 0.77
Any Cluster C PD IB 0.11 0.07 0.15
Avoidant PD IB 0.10 0.09 0.28
Dependent PD IB 0.19 0.20 0.36
Obsessive–compulsive PD IB -0.19 0.1 0.048
Passive-aggressive PD IB 0.39 0.11 0.0003
Depressive PD IB 0.20 0.12 0.10
NEO-PI-R
Neuroticism IB 0.004 0.001 0.002
TPQ
Harm Avoidance IB 0.014 0.005 0.01
Any Cluster B PD EB 0.27 0.07 0.0004
Antisocial PD EB 0.56 0.15 0.00017
Borderline PD EB 0.47 0.09 \0.0001
Histrionic PD EB 0.14 0.09 0.11
Narcissistic PD EB 0.08 0.08 0.35
NEO-PI-R
Agreeableness EB -0.002 0.002 0.36
Conscientiousness EB -0.006 0.002 0.001
TPQ
Novelty Seeking EB 0.013 0.007 0.06
p value for difference between those with andassessment of person-
ality disorder without the respective disorder or for effect of NEO-PI-
R or TPQ score (linear model adjusted for age and adult ADHD
subtype)
Estimate is the difference in psychosocial problems between those
with and without the respective disorder or PD or the difference in
psychosocial problems between probands with a difference of 1 in
NEO-PI-R or TPQ scores (see ‘‘Results’’ section for examples)
IB internalizing behavior, EB externalizing behavior
Internalizing and externalizing behavior
123
We conclude that AADHD in general is associated with
both internalizing and externalizing behavior. This finding
is in line with studies that show higher rates of AADHD,
internalizing and externalizing behavior in incarcerated
juveniles (Armistead et al. 1992; Carswell et al. 2004;
Sarris et al. 2000). The affection of internal psychological
environment and of the external world, i.e., the occurrence
of avoidance and anger, have to be taken into account in
future treatment strategies.
Inattentive subtype did not influence internalizing
behavior, while combined and hyperactive type had some
influence on externalizing behavior. This raises the question
whether the association with both internalizing and exter-
nalizing behavior might reflect an underlying emotional
dysregulation in AADHD. Factor analyses confirm the pre-
sence of emotional dysregulation that is one of the accessory
symptoms of AADHD described by Wender Utah criteria
(Reimherr et al. 2005). The concept of emotional dysregu-
lation has emerged from a content point of view, which was
verified post hoc in factor analyses. Neurobiological studies
provide evidence for the relevance of emotional dysregula-
tion in AADHD (Musser et al. 2013). Interestingly, medi-
cation with stimulants improves core symptoms and
emotional dysregulation (Reimherr et al. 2007).
The concept of internalizing/externalizing behavior is
based on formal statistical results, especially factor analyses
studies (Beelmann and Schneider 2003). Internalizing and
externalizing behavior is interpreted post hoc as over-con-
trolling and under-controlling (Esser et al. 2000) and can be
regarded as consequences of emotional dysregulation.
The relation between AADHD and comorbid conditions
remains unsolved. Usually, the onset of ADHD is earlier
than that of other axis I and axis II disorders so that it has to
be discussed whether ADHD is a psychological and
neurobiological vulnerability factor of these mental disor-
ders. A lifetime history of ADHD is also associated with
higher perceived stress that might labilize predisposed
individuals to comorbid conditions (Bernardi et al. 2012;
Meinzer et al. 2013). Results from recent studies suggest
common susceptibility genes in the etiology of AADHD
and comorbid conditions such as the brain-expressed GTP-
binding RAS-like 2 gene (DIRAS2) and Kv channel-
interacting protein 4 (KCNIP4) (Reif et al. 2011; Weißflog
et al. 2012). These genes might code for common neuro-
biological underpinnings of AADHD and related disorders
such as cell adhesion molecules (e.g., CDH13, ASTN2)
and regulators of synaptic plasticity (e.g., CTNNA2,
KALRN) (Lesch et al. 2008) or for the common underlying
personality traits Neuroticism and Harm Avoidance such as
the functional promoter polymorphism of the serotonin
transporter gene (5-HTTLPR) (Landaas et al. 2010).
These data present a replication and extension of a
previously published study (Jacob et al. 2007). The initial
study is about prevalence of comorbid axis I and axis II
disorders as well as personality traits, while the present
study is about internalizing and externalizing behavior in
an extended sample.
Differences in selection and sampling between our and
other studies have to be taken into account. The results for
comorbidity of clinical referral studies and catchment stud-
ies show distinct differences from each other accordingly.
The concept of internalizing and externalizing behavior has
several methodological limitations (Esser et al. 2000).
Mandatory definitions and standardized psychometric
assessment scales are missing in adults. Generally, inter-
nalizing behavior is characterized by the following: no typ-
ical age of onset, prevalence increases with age, and high
probability of remission. However, this does not apply to
personality traits and PDs. The factor analytic generation of
the concept of internalizing and externalizing behavior is
content free from hypothesis. The post hoc hypothesis of
under-controlling and over-controlling behavior is probably
convincing but not evidence based. There is a tendency to
underestimate internalizing behavior compared with exter-
nalizing behavior due to the obvious relevance of the latter in
interpersonal situations. The personal relevance, however, is
often not taken into account.
Taken together, the differentiation of internalizing and
externalizing behavior could be an interesting starting point for
further clinical, epidemiological, and neurobiological research
in children, adolescents, and adults affected with ADHD.
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