A systematic review and economic model of the effectiveness and ...

Description of underlying health
problem
ADHD (including HKD) is defined by the ‘core’
signs of inattention, hyperactivity and impulsivity,
and is characterised by an early onset. The
estimated prevalence for ADHD in school-aged
children varies widely (e.g. 3–7%), being
dependent on a number of variables including the
methods of ascertainment, the informants, the
population sampled, the diagnostic criteria
applied and the sex of the affected individual. For
example, prevalence rates may be lower when
diagnosed using the International Statistical
Classification of Diseases and Related Health
Problems (10th edition) (ICD-10) criteria (see
below) for hyperkinetic disorder. Data on
prevalence in adolescence and adulthood are
limited. The disorder is frequently observed in
greater numbers of males than females, with ratios
ranging from 2:1 to 9:1 depending on subtype
and setting. 2,3
In England and Wales, the prevalence of ADHD in
children 6–18 years of age has been estimated to
be about 5% (based on mid-1997 estimates). 4 The
British Child and Adolescent Mental Health
Survey conducted in 1999 examined a sample of
10,438 children and found 2.23% to have ADHD.
Of the 5212 males, 3.62% had ADHD compared
with 0.85% of the 5226 females in the sample
(p < 0.001). Overall, 1.41% of the sample was
classified as ADHD Combined Type, compared
with 0.67% and 0.16% Inattentive and Hyperactive
Type, respectively. 5
Aetiology
Research has indicated that the aetiology of
ADHD is of a multifactorial and complex nature.
Family, twin and adoption studies consistently
implicate the role of genetic factors. Molecular
genetic studies have focused on dopamine
receptors such as the D4 dopamine receptor gene
(DRD4), the mRNA of which appears to play a
role in cognitive and emotional functions.
A number of conditions have a very high risk for
the presence of ADHD symptoms, including
neurofibromatosis Type 1, 6 epilepsy, 7 very low
birth weight, 8,9 chronic tic disorders/Tourette’s
Chapter 2
Background
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Health Technology Assessment 2006; Vol. 10: No. 23
syndrome, developmental coordination disorders 10
and high functioning autism. 11 In addition,
numerous biological environmental risk factors
have been studied, such as diet, prenatal alcohol
and nicotine exposure, some of which appear to
account for selected cases. Many studies provide
strong evidence for the importance of psychosocial
adversity such as severe marital discord; however,
these factors tend to emerge as universal
predictors of a child’s emotional health and
adaptive functioning rather than being specific
predictors of ADHD. Although there is no single
pathophysiological profile of ADHD,
neurobiological research suggests that both genetic
and environmental factors modify the frontsubcortical
pathways in the brain that control
attention and motor behaviour. 12,13
Diagnosis
ICD-10, published in 1992, 14 details the diagnosis
of hyperkinetic disorders. Such disorders,
characterised by onset during childhood or
adolescence, feature both impaired attention and
overactivity evident in more than one situation
over a sustained period of time.
According to these guidelines, impaired attention
manifests itself in sufferers by premature breaking
off from tasks and leaving activities unfinished.
Overactivity implies excessive restlessness and is
judged in terms of normal expectations for the
situation, age and IQ of the individual involved.
Published in 2000, the fourth edition of the
Diagnostic and Statistical Manual of Mental Disorders
(DSM-IV) 2 cites five criteria to be considered in
the diagnosis of Attention deficit/hyperactivity
disorder:
A. At least six symptoms of inattention or
hyperactivity/impulsivity should have persisted
for at least 6 months to an extent inconsistent
with normal development.
B. Some symptoms must have been present
before 7 years of age.
C. Resulting impairment should be evident in
two or more settings.
D. Impairment should be clinically significant
with regard to social, academic or
occupational functioning.
3