Pervasive developmental disorder with attention deficit hyperactivity disorder-like symptoms and mismatch negativity
Masayuki Sawada, MD, Department of Psychiatry, Nara Medical University School of Medicine, 840 Shijocho Kashihara City, Nara 634-8522, Japan. Phone: +81-744-22-3051; Fax: +81-744-22-3854; E-mail: firstname.lastname@example.org
The present study examined the correlation between the attention deficit hyperactivity disorder (ADHD) Rating Scale-IV Japanese version (ADHD RS-IV-J) score and mismatch negativity (MMN), in 10 pervasive developmental disorder (PDD) children with ADHD-like symptoms, and examined whether MMN become the objective measure to assess the severity of ADHD-like symptoms in PDD children. Consequently, score of ADHD RS-IV-J had a positive correlative tendency with MMN latency and had a significant strong negative correlation with MMN amplitude. Therefore, MMN may become an objective measure to assess the severity of ADHD-like symptoms in PDD children.
EVENT-RELATED POTENTIALS (ERP) contribute to the research in cognitive function as physiological measures that can be easily measured and which are non-intrusive. Therefore, ERP are useful measures to examine cognitive disturbance of children with developmental disorder. Mismatch negativity (MMN), one of the ERP, reflects an automatic cerebral discrimination process, not under attentive control.1 We previously indicated that MMN might be an objective measure of the severity of attention-deficit–hyperactivity disorder (ADHD) symptoms in ADHD patients.2
In the DSM-IV, comorbidity of pervasive developmental disorder (PDD) and ADHD is not recognized and also PDD is an exclusion criterion of ADHD.3 In recent years, however, an increasing number of cases have involved difficulty in distinguishing PDD from ADHD. Therefore, an objective measure of ADHD-like symptoms in PDD patients is needed. In the present study we examine the correlation between the ADHD Rating Scale-IV Japanese Version (ADHD RS-IV-J)4 score and MMN, in PDD children with ADHD-like symptoms.
Ten children diagnosed with PDD based on DSM-IV,3 participated in the present study. They also had ADHD-like symptoms. All subjects were male and right-handed. Their mean age was 8.60 ± 1.65 years. Their mean Wechsler Intelligence Scale for Children–Third Edition Full/Verbal/Performance Intelligence Quotient scores were 101 ± 15.7, 107 ± 21.8, and 93.2 ± 10.5, respectively. The mean ADHD RS-IV-J score was 25.4 ± 5.95.
All subjects and/or their parents gave informed consent to participate in the study. In addition, this study was approved by Institutional Review Board of Nara Medical University Hospital.
MMN was measured using auditory odd-ball tasks. An NEC Multi Stim was used as the auditory stimulus system (NEC, Tokyo, Japan). Standard stimuli (P = 0.9) were tone bursts at 1000 Hz and deviant stimuli (P = 0.1) were tones at 1100 Hz, with all stimuli lasting 50 ms at 500-ms intervals and an intensity of 80 dB. These infrequent and frequent stimuli were given in random order through headphones. MMN was measured while the subjects were reading books of their choice, without paying particular attention to the auditory stimuli given, as instructed (READ condition).
MMN was recorded with an NEC Synax 1200 (NEC, Tokyo, Japan). Electroencephalograms were obtained at Fz, Cz and Pz on the scalp using disk electrodes, with both ear lobes as the reference electrode sites. MMN was analyzed during the period between 100 ms pre-stimulus and 400 ms post-stimulus. The amplitude was measured with the potential of 0 ms latency as the baseline.
One hundred responses to infrequent deviant stimuli and 900 responses to frequent standard stimuli were averaged separately. The waveform of the latter responses was subtracted from that of the former. MMN was identified as negativity with the peak latency at 100–250 ms based on the subtraction waveform.
The correlation between the ADHD RS-IV-J score and MMN was examined using the Pearson coefficient of correlation (r). Data are expressed as the mean ± SD. Data analyses were conducted using SPSS version 11.0 for Windows (SPSS, Tokyo, Japan).
As shown in Table 1, score of ADHD RS-IV-J had a significant strong negative correlation with MMN amplitude recorded at Cz and Pz and had a positive correlative tendency with MMN latency recorded at Fz and Cz.
Table 1. ADHD RS-IV-J score and MMN measures
We previously reported that MMN amplitudes of the ADHD children were smaller than those of the healthy control children.5 But neither MMN amplitude nor latency has been reported to differ significantly between the adult ADHD group and the adult healthy control group.6,7 Therefore, in the ADHD group, MMN dysfunction might be able to improve with maturation.6,7 In addition, Achenbach et al. reported that symptoms of hyperactivity/impulsiveness were ameliorated with maturation and that symptoms of attention deficit remained in a large number of the ADHD combined-type children.8 Therefore, MMN has been indicated to be associated with hyperactivity/impulsiveness of ADHD.
We also reported that ADHD RS-IV-J score had a significant strong positive correlation with MMN latency and had a significant strong negative correlation with MMN amplitude in the ADHD combined-type group.2 Therefore, MMN might be an objective measure of severity of ADHD symptoms in the ADHD group.
The present study indicates that there may be a correlation between ADHD RS-IV-J score and MMN in the PDD group with ADHD-like symptoms as well as in the ADHD group. Therefore, MMN may be an objective measure of the severity of ADHD-like symptoms in the PDD group with ADHD-like symptoms. We indicate a strong possibility that hyperactivity/impulsiveness and attention deficit associated with PDD are not completely different from those associated with ADHD when considered in the context of ERP. Further studies are needed to determine whether there are PDD patients with comorbid ADHD.