Impact of anxiety disorders on attentional functions in children with ADHD

Abstract

Introduction

The impact of internalizing comorbid disorders on cognitive functions in attention-deficit hyperactivity disorder (ADHD) is hardly understood. While inconsistent findings exist with respect to the modulating effect of anxiety on impulsivity in ADHD, only few neuropsychological studies focused on other attention parameters. This is the first study that examines the influence of anxiety disorders (ANX) on ADHD in a model-oriented approach including selectivity and intensity parameters of attention.

Methods

Children with ADHD, ADHD + ANX and healthy controls (n = 34 for each group, all aged 8–15 years) participated in five neuropsychological tasks (alertness, sustained attention, divided attention, go/no-go and set-shifting). Group differences were evaluated using analysis of variance (ANOVA) for each dependent variable, with group as independent variable.

Results

Data indicated that children with ADHD performed worse than healthy controls with regard to almost all parameters of attention. While ANX had no mitigating effect on impulsivity in ADHD, performance in sustained attention and selective attention tasks of children with ADHD + ANX was better than that of children with ADHD only.

Limitations

Since the present data were derived from a large neuropsychological data base which focused primary on children with ADHD and different comorbidities no comparison to a “pure” ANX group was possible.

Conclusions

These findings might indicate that ADHD + ANX constitute a cognitively distinct subtype, with possible individual symptomatology, development and therapeutic needs. Further investigations are needed to clarify the specificity of these findings and to disentangle the impact of trait versus state anxiety on neuropsychological performance in children with ADHD.

Introduction

ADHD is a heterogeneous neuropsychiatric disorder affecting between 4 and 10% of the childhood population (Skounti et al., 2007). It is characterized by developmentally inappropriate levels of activity and impulsivity as well as inattentive behaviour. Numerous studies have investigated individuals with ADHD without comorbid disorders in comparison to healthy controls using various neuropsychological measurements. Nevertheless, ADHD very often co-occurs with other psychiatric disorders (Elia et al., 2008), which may influence the performance on different neuropsychological tests (for reviews see Willcutt et al., 2005, Seidman, 2006). For example, it has been well established that children with ADHD who also suffer from externalizing disorders show poorer neuropsychological performance (e. g. response inhibition), as compared to children with ADHD alone (for a meta-analysis see Lijffijt et al., 2005). There is even an intensive discussion regarding the comorbidity of ADHD and disruptive behavior disorders (DBD) as two distinct disorders or a “true hybrid” (e. g. DSM-IV versus ICD-10). However, less is known about the impact of internalizing comorbid disorders on cognitive functions in ADHD.

Approximately 25% to 50% of all children with ADHD exhibit an anxiety disorder (ANX) and the combination of both seems to have a significant impact on neuropsychological test performance (for a review see Schatz and Rostain, 2006). In line with the evidence on the relationship between ADHD and externalizing disorder, data from the Multimodal Treatment Study of Children with ADHD (MTA) indicate that the co-occurrence of ADHD + ANX seems to be a distinct clinical subtype with its own implications for aetiology, assessment, and treatment (for reviews see Hinshaw, 2007, Jarrett and Ollendick, 2008).

Current models of ADHD suggest that it is best characterized as a disorder of impaired executive functions or reduced inhibition control (for a review see Nigg, 2001; for a meta-analysis see Willcutt et al., 2005). By contrast, it has been suggested that ANX are associated with increased control of inhibition (Oosterlaan and Sergeant, 1998, Degnan and Fox, 2007). In addition, a strong tendency for response inhibition in children seems to be a powerful predictor of later ANX (for a review see Biederman et al., 1995). Finally, it has been suggested that ANX might act as a protective factor against the development of ADHD (Nigg, 2006). Thus, most of the existing studies examined the impact of ANX on inhibitory control and impulsivity in children with ADHD.

Previous neuropsychological studies have provided conflicting results whether children with ADHD + ANX showed better inhibitory control when compared to children with pure ADHD (Pliszka, 1992, Manassis et al., 2000) or not (Newcorn et al., 2001). Based on the review of Schatz and Rostain (2006) most studies did not find a robust effect of ANX on ADHD and the authors concluded that ANX may partially inhibit the impulsivity seen in ADHD. However, a more recent neuropsychological investigation has shown that children with ADHD + ANX did not differ from those with pure ADHD with respect to response inhibition (Korenblum et al., 2007).

To date, only a few studies have investigated the impact of ANX on other cognitive domains in ADHD. Tannock et al. (1995) found a poorer working memory performance of children with ADHD + ANX compared to those with pure ADHD. By contrast, more recently, Manassis (2007) could not replicate these finding. Nevertheless, since the MTA revealed that children with ADHD + ANX are characterized by an increased treatment response and a better prognosis than those with pure ADHD (Jensen et al., 2001) one could speculate, that children with ADHD + ANX might exhibit a less impaired cognitive performance than those with ADHD alone. However, to our knowledge, no study has examined the influence of ANX in ADHD on attention in a model-oriented approach including a comprehensive assessment of different attentional functions.

Taken together, the available data suggest that the comorbidity of ANX is a possible modulator of the cognitive performance in children with ADHD. There is, however, still a lack of comprehensive neuropsychological data to characterize the attentional performance of children with ADHD + ANX compared to those with pure ADHD and healthy controls. Therefore we examined whether different intensity and selectivity parameters of attention as well as the supervisory attentional control mechanism vary due to comorbid ANX in children with ADHD. Data were assessed using different computerized attention tests according to a model-oriented approach (Van Zomeren and Brouwer, 1994; see also Fig. 1).

Based on the existing literature, we hypothesized that children with ADHD and ADHD + ANX would not differ in respect to measures of response inhibition (Korenblum et al., 2007), but would perform worse than healthy controls. Furthermore, with regard to intensity aspects of attention, we hypothesized that children with ADHD + ANX would present a less impaired or at least comparable performance vs. children with pure ADHD (Jensen et al., 2001, for review see Hinshaw, 2007).