The diagnosis and assessment of ADHD can be a difficult process for both parents and their child. The symptoms of ADHD are clustered according to criteria set out in clinical diagnostic systems.
Diagnostic criteria for ADHD
The major clinical diagnostic systems for children’s mental and emotional disorders are the International Classification of Diseases, 10th edition (ICD-10) Classification of Mental and Behavioural Disorders (WHO 1993) and the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) (American Psychiatric Association 1994).
Characteristics of the diagnostic systems
The ICD-10 consists of a volume of clinical descriptions and diagnostic guidelines, and a separate volume containing diagnostic criteria for research. The DSM-IV uses operational criteria and does not separate clinical from research criteria. The ICD-10 is an exclusive categorical system that does not allow multiple diagnoses, while DSM-IV allows multiple diagnoses to be applied in order of importance at presentation.
The DSM-IV (and the earlier DSM-III-R) were developed using field trials and testing items against clinician diagnoses (Hart, Lahey, Loeber et al 1995; Frick, Lahey and Applegate 1994; Spitzer, Davies and Barkley 1990), although expert committees made final category decisions. The DSM-IV criteria for ADHD are listed below. The ICD-10 clinical description and diagnostic criteria for research are listed in Appendix A.
DSM-IV criteria ÷ attention deficit/hyperactivity disorder
A. Either (1) or (2):
(1) six (or more) of the following symptoms of inattention have persisted for at least six months to a degree that is maladaptive and inconsistent with developmental level:
(a) often fails to give close attention to details or makes careless mistakes in school work, work or other activities;
(b) often has difficulty sustaining attention in tasks or play activities;
(c) often does not seem to listen when spoken to directly;
(d) often does not follow through on instructions and fails to finish school work, chores, or duties in the workplace (not due to oppositional behaviour or failure to understand instructions);
(e) often has difficulty organising tasks and activities;
(f) often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (such as school work or homework);
(g) often loses things necessary for tasks or activities (eg toys, school assignments, pencils, books or tools) ;
(h) is often easily distracted by extraneous stimuli;
(i) is often forgetful in daily activities.
(2) six (or more) of the following symptoms of hyperactivity÷impulsivity have persisted for at least six months to a degree that is maladaptive and inconsistent with developmental level:
(a) often fidgets with hands or feet or squirms in seat;
(b) often leaves seat in classroom or in other situations in which remaining seated is expected;
(c) often runs about or climbs excessively in situations in which it is inappropriate (in adolescents or adults, may be limited to subjective feelings of restlessness);
(d) often has difficulty playing or engaging in leisure activities quietly;
(e) is often “on the go” or often acts as if driven by a motor;
(f) often talks excessively.
(g) often blurts out answers before questions have been completed;
(h) often has difficulty awaiting turn;
(i) often interrupts or intrudes on others (eg Îbutts intoâ conversations or games).
B. Some hyperactiveöimpulsive or inattentive symptoms that caused impairment were present before age seven years .
C. Some impairment from the symptoms is present in two or more settings (eg at school [or work] and at home).
D. There must be clear evidence of clinically significant impairment in social, academic, or occupational functioning.
E. The symptoms do not occur exclusively during the course of a pervasive developmental disorder, schizophrenia or other psychotic disorder and are not better accounted for by another mental disorder (eg mood disorder, anxiety disorder, dissociative disorder, or a personality disorder).
The DSM-IV codes ADHD are as follows (ICD-10 research codes are almost identical):
314.01 Attention-deficit/hyperactivity disorder, combined type: if both criteria A1 and A2 are met for the past six months.
314.00 Attention-deficit/hyperactivity disorder, predominantly inattentive type: if criterion A1 is met but criterion A2 is not met for the past six months.
314.01 Attention-deficit/hyperactivity disorder, predominantly hyperactive-impulsive type: if criterion A2 is met but criterion A1 is not met for the past six months.
The criteria for diagnosis of ADHD in DSM-IV and hyperkinetic disorder in ICD-10 are almost identical criteria related to inattention and hyperactivityöimpulsivity.
While DSM-IV allows multiple diagnoses with co-morbid conditions such as Conduct Disorder, ICD-10 contains a separate category of the Hyperkinetic Conduct Disorder. This difference has important implications for prevalence studies.
The DSM-IV and ICD-10 diagnostic criteria for research both require that symptoms should be observed in two out of three settings (home/school/clinic). This represents a change from DSM-III-R which allowed a diagnosis either at home or at school.
Finally, the requirement for clinically significant impairment in social, academic or occupational functioning is an important addition to previous criteria.
Unresolved diagnostic issues
Barkley (1995a) has outlined a number of as yet unresolved issues in relation to the DSM-IV criteria which allow diagnosis of the predominantly inattentive, predominantly hyperactiveöimpulsive or combined types of ADHD. Barkley pointed out that it is not clear whether the predominantly inattentive type of ADHD is a subtype or a separate disorder. It is also unclear whether the predominantly hyperactiveöimpulsive type is separate from the combined type or simply an earlier developmental stage. Follow-up studies (Fisher, Barkley, Fletcher et al 1993; Weiss and Hechtman 1993) have found that childhood symptoms of hyperactivity are related to adolescent negative outcomes, while those of inattention are much less so, if at all.
Duration of symptoms
There appears to be little research support for the six-month duration requirement and it has been suggested that young preschool children may show remission within twelve months (Barkley 1995a; Campbell 1990; Beitchman, Wekerle and Hood 1987; Palfrey, Levine, Walker et al 1985). Thus, symptoms that persist for at least twelve months may be a more rigorous criterion.
DSM-IV (American Psychiatric Association 1994) requires agreement by at least two or more informants (parent, teacher, employer). As the degree of demonstrated agreement between informants is modest (0.3 to 0.5) (Achenbach, McConaughy and Howell 1987), Barkley suggested that this requirement may be combined with co-morbidity issues ( children identified by both parents and teachers are more likely to have co-morbid behaviour problems). This issue requires more research.
Barkley (1991) also questioned how well the diagnostic thresholds set for the two categorisation systems would apply to age groups outside those used in the field trial (age 4ö16 years).
These thresholds may inappropriately diagnose young preschool children as ADHD (false positives), while a smaller than expected percentage of adults would meet the criteria (false negatives). Barkley (1995a) pointed out that the predominantly hyperactiveöimpulsive type of ADHD may be a developmentally earlier stage of the combined type ( inattentive/hyperactiveöimpulsive). Murphy and Barkley (1995) have developed preliminary normative data on DSM-IV criteria for adults.
The question of whether or not the criteria should be adjusted for the gender of the children being diagnosed was also raised in Barkley (1995a). This issue requires further study, and was not fully resolved at a meeting of the United States National Institute of Mental Health (NIMH) in November 1994. Data presented at the conference suggested that males with ADHD demonstrate more aggressive (oppositionalödefiant) behaviour and Conduct Disorder symptoms than do females, whether drawn from clinical or community samples.
Key points – diagnostic systems
The DSM-IV and ICD-10 are the current diagnostic systems for categorising disruptive behaviour disorders. The research criteria in these two texts are similar, but not identical. ICD-10 permits compound diagnoses, whereas DSM -IV allows multiple diagnoses. As a minimum, the criteria set down in DSM-IV should be met before a diagnosis of ADHD is made. A number of unresolved issues remain in relation to, among others, age, gender, diagnostic thresholds and co-morbidity.
Approaches to diagnosis
The categorical approach considers that symptoms and signs stem from a single disorder, which is clearly abnormal. For example, tonsillitis is clearly a categorical diagnosis. The presence of inflamed tonsils and a sore throat is clearly abnormal÷the symptoms and signs are caused by a single disorder.
Similarly, in ADHD, the categorical approach considers that all the diverse behavioural symptoms stem from a single disorder. Each case is assigned to only one category and the assumption is made that membership in one category precludes membership in another. Thus, the precise order in which competing diagnoses are made will have profound effects on the assignment of cases.
The trait approach considers behaviour as a continuum, and that certain conditions represent an extreme end of this spectrum rather than a discrete abnormal category. In other words, disordered behaviour represents an extreme position on one or more of a number of independent traits or dimensions. Significant dimensions of a trait are defined by cutoff criteria which may be statistical (such as two or three standard deviations beyond the mean), or a priori (such as five or more symptoms).
Prevalence rates using different approaches
Rutter, Tizard and Whitmore (1970) used categorical approaches in which hyperactivity had to be predominant, and unaccompanied by other disorders, giving rise to a very low (0.11 per cent) prevalence for hyperactivity in 10ö11 year-old children.
Using a categorical approach, Glow (1980) (in Adelaide) found a prevalence of 2.26 per cent for severe hyperactive disorder in boys and 0.59 per cent in girls. Using a trait approach, Glow (1980) found a prevalence rate of 6.06 per cent for significant (>2 standard deviations above scale mean), and 1.66 per cent for severe (>3 standard deviations above the scale mean) hyperactivity disorder.
In Canada, the Ontario cohort study (Szatmari, Offord and Boyle 1989b) separated subjects with ADHD symptoms above threshold (6 per cent of children) into pervasive (18 per cent of ADHD) where two sources agree (parent/ teacher or parent/youth); or situational (24 per cent ÷ parent only; or 66 per cent ÷ teacher/youth only). Their study also provides valuable information on the relative prevalence of ADHD with and without hyperactivity and at different ages. These studies show the importance of procedures and informants in arriving at a diagnosis and in determining the prevalence of ADHD. In an Australian and New Zealand study with a control population, Tripp and Luk (1997) showed that whether symptoms are pervasive or situational is determined by combined observersâ reports, not whether hyperactivity is observed at a clinical consultation.
Fergusson and Horwood (1995) have examined the predictive validity of categorically and dimensionally scored measures of disruptive childhood behaviours and concluded that disruptive behaviours have dimensional properties ranging from none to severe. They caution that the use of categorical criteria may have less than optimal predictive validity.