The Role of Neuropsychologic Tests in the Diagnosis of Attention Deficit Hyperactivity Disorder

Attention, memory, executive function, language, and visual-motor skills were evaluated in a sample of 621 children, 6 to 11 years old, to assess the discriminant validity of neuropsychologic testing. Attention deficit hyperactivity disorder cases (249) and controls (372) were identified and tested. Analysis of covariance, nonparametric comparison tests, effect sizes, discriminant function, factor analyses, and receiver-operator characteristics curve analyses were used to establish the best diagnostic cutoff points for each variable. Statistically significant differences were found on cognitive effort, auditory skills, continuous performance test, working memory, visual-motor skills, verbal comprehension, and executive function measures (P < 0.05); however, the effect of group sizes was low to modest (0.24 to 0.54). Receiver-operator characteristics curve analysis showed modest sensitivity and low specificity, demonstrating that an important proportion of the variance in test scores was overlapping. Factor analysis of neuropsychologic testing results revealed a structure of six factors each for attention deficit hyperactivity disorder, control, and combined samples. The latent variables produced one discriminant function with a total correct classification accuracy of 61.9%. Neuropsychologic tests should be used as Attention Deficit Hyperactivity Disorder diagnostic tools with caution, but they hold promise for identifying core cognitive deficits and processes that can aid prevention and intervention.

Introduction

It has been assumed that attention deficit hyperactivity disorder (ADHD) is a neurologic, behavioral, and cognitive disorder [1]. Symptoms of inattention, hyperactivity, and impulsivity are considered the main behavioral characteristics of ADHD and have been incorporated into diagnostic systems with an estimated prevalence of 3% to 5% in school-age children [2]. It has also been reported that ADHD is frequently comorbid with both externalizing and internalizing psychopathologies, such as oppositional defiant disorder, conduct disorder, depression, bipolar disorder, alcoholism, and substance abuse [3], [4], [5]. Additionally, attention and working memory impairment, metalinguistic deficiency, and executive dysfunction are considered the core cognitive problems related to ADHD [6], [7].

A gold-standard procedure for ADHD diagnosis includes psychiatric, psychologic, and neurologic evaluations. Psychiatric and psychologic interviews are important, given both the difficulty in distinguishing ADHD from other child psychiatric disorders and the high risk of having ADHD present concurrently with other psychiatric disorders. Psychiatric assessment is becoming mandatory in genetic studies, and clinical-medical and neurologic evaluations are recommended in all cases, to complete the ADHD diagnostic criterion E of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) [2], which requires ruling out other conditions that might better explain the symptoms. None of the objective laboratory exams have demonstrated validity for ADHD diagnosis [2], [8], [9], [10].

Currently, rating scales are commonly used for ADHD studies, and there is consensus regarding the need for a multirater and multimethod process of ADHD diagnosis [11]. In other words, a more valid diagnosis requires information from multiple reporters about the individual’s typical behavior in several settings (typically, at home and at school or at work). Additionally, formal and informal observations, anecdotal reports, semistructured clinical interviews, and behavioral checklists are all optional methods that should be integrated when diagnosing ADHD. Self-reports are recommended as well, although individuals with ADHD tend to be poor reporters of their own functioning [12], [13]. However, findings in previous confirmatory factor analyses of rating scales have demonstrated that most ADHD symptoms contain more source than trait variance, thus providing weak evidence for the convergent and discriminant validity of the symptoms as measured by these rating scales [14] and suggesting that a multimethod approach might add validity to the diagnosis.

Many studies report that ADHD children perform poorly on tasks that assess continuous vigilance, processing speed, verbal learning and memory, working memory, phonological awareness, and executive function [1], [15], [16], [17], [18], [19]. Several meta-analytic reviews have been published on the validity of intellectual functioning [20], inhibitory control [21], [22], and executive function [23], [24] as predominant cognitive characteristics of ADHD.

The debate surrounding the identification of the core cognitive impairment has been the primary focus of multiple analyses [1], [21], [23], [25], [26]. The discussion revolves around the question of whether ADHD cognitive impairment is specific [21] or generalized [20], [25]. Another point of contention is whether ADHD is a multiple domain cognitive deficit or an underlying basic impairment affecting all kinds of functions that rely on that particular process [16], [25]. It has been argued that, although there are several specific cognitive problems, the tasks, which are designed to assess brain damage, do not have enough sensitivity to detect the mild disabilities present in most of the affected ADHD patients.

We hypothesized that construction of multiple levels of analysis can demonstrate the validity of a neuropsychologic battery to differentiate between ADHD and control children and predicted that neuropsychologic tests would have a high degree of accuracy for making the ADHD diagnosis.