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Aims: The aim of the present study was to verify the comorbidity of conduct disorder (CD) and behavioral/developmental disorders in children and adolescents, and to examine the traits of CD comorbid with them.
Methods: Subjects were 64 children (60 boys, four girls) who were resident at three institutions for delinquent children or who were conduct-disordered outpatients of a university hospital aged under 18 years. A diagnostic interview was carried out by experienced child psychiatrists and the intelligence score and the Adverse Childhood Experiences score were measured by a licensed psychologist.
Results: A total of 57 children were diagnosed as having CD, of whom 26 (45.6%) were diagnosed with comorbid attention-deficit–hyperactivity disorder (ADHD), 12 were diagnosed with comorbid pervasive developmental disorder (PDD, 21,1%), and 19 (33.3%) had no comorbidity of either disorder. Six children (18.8% of CD comorbid with ADHD) met the criteria for both ADHD and PDD. The group with comorbid PDD was significantly younger at onset (F = 6.51, P = 0.003) and included unsocialized type more frequently (χ2 = 6.66, P = 0.036) compared with the other two groups.
Conclusions: Clinicians should be aware that not only ADHD but also PDD may be comorbid with CD. Establishment of the correct diagnosis is important because recognizing the presence of PDD will enable us to provide appropriate treatment and guidance, which may improve prognosis.
SINCE THE INCLUSION of conduct disorder (CD) in the third edition of the DSM, a close association has been suggested between CD and attention-deficit–hyperactivity disorder (ADHD). Holmes et al., in their review of risk factors in childhood that lead to CD and antisocial personality disorder (APD), held that impulse control dysfunction and the presence of hyperactivity and inattention are the most highly related predisposing factors for the presentation of antisocial behavior.1 They asserted that ADHD could contribute greatly to problematic behavior and antisocial acts, and the hyperactivity component of ADHD was very important to the development of later CD and APD.
The association between pervasive developmental disorder (PDD) and CD or delinquency, in contrast, has received surprisingly little attention. Such comorbidity has generally been considered to constitute a very small proportion of the cases of CD. Siponmaa et al., however, reported that 15% of 126 young offenders (15–22 years) had a definite diagnosis of ADHD, and another 15% had PDD, including 12% with PDD not otherwise specified (PDD-NOS) and 3% with Asperger's syndrome, and that the rate of PDD found was particularly striking.2
The primary objective of the present study, therefore, was to answer the question of whether it is sufficient to consider ADHD as the unique behavioral/developmental disorder comorbid with CD. Our preliminary assumption was that the comorbidity of PDD with CD is more common than has been previously considered, so we carried out a diagnostic interview to assess the comorbidity of behavioral/developmental disorder with CD.
If our assumption that the comorbidity of PDD with CD is more common than previously thought is true, a possible explanation for the lack of attention to comorbidity of PDD may be that a substantial number of children with PDD are misdiagnosed as having ADHD due to the overlapping hyperactivity and inattention symptoms. Therefore, to confirm this assumption, the second aim of the present study was to investigate the overlapping conditions between PDD and ADHD comorbid with CD.
We also examined the differences in traits of CD depending on the type of comorbid behavioral/developmental disorder. This was the third aim of the present study.
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Table 1 lists the profiles of all 57 subjects. There were no significant differences between the three types of facilities with respect to gender ratio, age at onset, types of CD, types of comorbid behavioral/developmental disorders, FIQ and ACE scores. Although the number of corresponding items for the diagnostic CD criteria for the subjects from hospital D were relatively high, we must consider the result to be preliminary because the number of subjects was so small.
Table 1. Subject profiles
| ||Facilities A and B (n = 25) (Mean ± SD)||Facility C (n = 25) (Mean ± SD)||Hospital D (n = 7) (Mean ± SD)|
|Boys : Girls, n||23:2||25:0||6:1|
|Age at the time of study (years)||14.3 ± 1.1||16.8 ± 1.2||15.0 ± 1.7|
|Onset age (years)||10.0 ± 2.7||13.7 ± 1.9||11.6 ± 2.9|
|Socialized type : Unsocialized type, n||14:11||20:5||3:4|
|Comorbid with ADHD, n (%)||8 (32.0)||13 (52.0)||5 (71.4)|
|Comorbid with PDD, n (%)||8 (32.0)||2 (8.0)||2 (28.6)|
|Comorbid with ODD, n (%)||9 (36.0)||11 (44.0)||4 (57.1)|
|FIQ||87.9 ± 11.3||94.9 ± 11.7||91.7 ± 12.3|
|ACE score||2.0 ± 2.1||1.1 ± 1.4||1.5 ± 1.5|
|CD criteria||6.6 ± 2.8||5.2 ± 1.7||9.1 ± 4.1|
|Aggression to people and animals||2.3 ± 1.8||1.6 ± 1.2||2.3 ± 2.1|
|Destruction of property||0.4 ± 0.5||0.3 ± 0.5||0.6 ± 0.8|
|Deceitfulness or theft||2.0 ± 0.9||1.3 ± 0.8||3.0 ± 1.6|
|Serious violations of rules||2.0 ± 1.3||2.0 ± 1.2||3.3 ± 1.5|
On applying the exclusion criteria of DSM-IV preferring PDD over ADHD, 26 children (25 boys, one girl; 45.6% of the subjects; mean age 15.8 ± 1.4 years) were included in the ADHD group, 12 children (11 boys, one girl; 21.1% of the subjects; mean age 14.0 ± 1.8 years) were included in the PDD group, and 19 children (18 boys, one girl; 33.3% of the subjects; mean age 16.1 ± 1.6 years) were included in the NC group. Only four children including three with ADHD and one with PDD were diagnosed prior to the study.
By neglecting the exclusion criteria of DSM preferring PDD over ADHD, six subjects satisfied the criteria for both ADHD and PDD, representing 18.8% of those who met the criteria for ADHD (32 out of 57 subjects) and 50% of those who met the criteria for PDD (12 of 57 subjects). Of the children diagnosed as having CD, seven (12.3%) had an IQ below 79 (one with mental retardation and six with borderline intellectual functioning). The overlap of behavioral/developmental disorder is shown in Fig. 1.
Figure 1. Comorbid behavioral and developmental disorders of children with conduct disorder. (●) Oppositional defiant disorder; () absence of oppositional defiant disorder. ADHD, attention-deficit–hyperactivity disorder; BIF, borderline intellectual functioning (full-scale IQ between 70 and 79); MR, mental retardation; PDD, pervasive developmental disorder.
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Table 2 shows the profiles of the three groups. The mean onset age of the PDD group was 9.3 ± 3.1 years, which was significantly younger than that of the other two groups (F = 6.51, P = 0.003). Of this group, 66.7% (eight of 12 subjects) had the unsocialized type, which occurred more frequently (χ2 = 6.66, P = 0.036) compared with the other two groups. The ADHD group was comorbid with ODD more frequently compared with the NC group (χ2 = 6.05, P = 0.049). There were no significant differences between the three groups with respect to FIQ, ACE scores and CD criteria.
Table 2. Subject profiles vs comorbidity
| ||ADHD group (n = 26) (Mean ± SD)||PDD group (n = 12) (Mean ± SD)||NC group (n = 19) (Mean ± SD)||χ2 or F||Multiple comparisons|
|Boys : Girls, n||25:1||11:1||18:1||0.33†|| |
|Onset age (years)||12.5 ± 2.7||9.3 ± 3.1||12.4 ± 2.5||6.51*‡||PDD < ADHD, NC|
|Unsocialized type, n (%)||7 (26.9)||8 (66.7)||5 (26.3)||6.66*†||PDD > ADHD, NC|
|Comorbid with ODD, n (%)||15 (57.7)||5 (41.7)||4 (21.1)||6.05*†||ADHD > NC|
|FIQ||89.6 ± 10.1||88.1 ± 11.6||96.1 ± 13.1||2.77‡|| |
|ACE score||1.8 ± 1.7||1.1 ± 1.1||1.6 ± 2.1||0.66‡|| |
|CD criteria||6.9 ± 2.6||5.8 ± 3.2||5.8 ± 2.8||1.03‡|| |
| Aggression to people and animals||2.2 ± 1.4||1.4 ± 1.9||2.0 ± 1.7||1.01‡|| |
| Destruction of property||0.4 ± 0.5||0.5 ± 0.7||0.3 ± 0.5||0.77‡|| |
| Deceitfulness or theft||1.7 ± 1.2||2.3 ± 1.1||1.6 ± 1.0||1.82‡|| |
| Serious violations of rules||2.5 ± 1.5||1.5 ± 1.2||2.0 ± 1.1||2.72‡|| |