2 Clinical need and practice
2.1 ADHD is defined by the core signs of inattention, hyperactivity and impulsiveness. There are two main sets of diagnostic criteria in current use. The Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV) criteria define ADHD broadly to include three subtypes: a combined subtype in which all three core signs are present; a predominantly inattentive subtype in which inattention is present but not hyperactivity or impulsiveness; and a predominantly hyperactive-impulsive subtype in which hyperactivity and impulsiveness are present but not inattention. The DSM-IV definition of severe combined-type ADHD is similar to the International Classification of Mental and Behavioural Disorders 10th revision (ICD-10) definition of hyperkinetic disorder. The ICD-10 definition of hyperkinetic disorder requires abnormal levels of inattention, hyperactivity and impulsivity to be present for at least 6 months.
2.2 ADHD often coexists with other conditions such as oppositional defiant disorder, conduct disorder, learning disorders, anxiety, depression, epilepsy, tic disorders and Tourette's syndrome.
2.3 Estimates of the prevalence of ADHD vary widely within and between countries. It is estimated that around 5% of school-aged children and adolescents would meet the DSM-IV diagnostic criteria for ADHD, equivalent to 366,000 children and adolescents in England and Wales, but not all of these children and adolescents would require treatment. Approximately 1% of school-aged children and adolescents would meet the diagnostic criteria for hyperkinetic disorder.
2.4 ADHD affects children and adolescents in different ways and degrees, but the consequences of severe ADHD can be serious for both the individual and their family and carers. Children with severe ADHD often have low self-esteem, develop emotional and social problems, and frequently underachieve at school. The signs of ADHD may persist into adolescence and adulthood, and are often associated with continuing emotional and social problems, substance misuse, unemployment, and involvement in crime.
2.5 Current treatments for ADHD include a range of social, psychological and behavioural interventions. These are mainly aimed at the child, but sometimes involve parents and/or guardians and teachers. Dietary interventions are often used when particular foods aggravate hyperactivity. The central nervous system (CNS) stimulants methylphenidate and dexamfetamine have been used in the treatment of ADHD for many years. Atomoxetine has been introduced more recently. Clinicians sometimes prescribe tricyclic and other antidepressant drugs, although these are not licensed for ADHD.