What are the three subtypes of ADHD?

ADHD is defined in many different ways. In the 1950s, the emphasis was on the hyperactivity characteristic of the disorder. Various terms were used at the time, such as hyperkinetic syndrome and hyperactive child syndrome . Over time, attention for hyperactivity and concentration problems decreased. In the DSM-III it was recognized that attention deficit disorder (ADD) could occur with and without hyperactivity. Attention Deficit Hyperactivity Disorder (ADHD) was not included in the revised version of the DSM-III . This disorder is also recognized by dimensional classification systems.

Research suggested that ADHD consists of two components: inattention and hyperactivity-impulsivity. There is a lot of cross-cultural evidence for the validity of these factors. Although both components have unique genetic influences, they are interrelated as a result of shared genetic influences.

DSM classification

The DSM states that the two factors (inattention and hyperactivity-impulsivity) together form three subtypes of ADHD:

• Inattentive type (ADHD inattentive; ADHD-I)
• Hyperactive-impulsive type (ADHD-hyperactive-impulsive; ADHD-HI)
• Combined type (ADHD-combined; ADHD-C)

The diagnostic criteria state that there must be symptoms of inattention and hyperactivity-impulsivity, respectively. the diagnostic criteria state that some symptoms must be present before the age of 12 and for at least six months. Because all symptoms occur to some extent in normally developing children and may vary with the level of development, the diagnosis is only made if the symptoms are excessive and occur in at least two different settings (for example at home and at school). The symptoms must also interfere with the social and academic functioning of the child.

What are the primary characteristics of ADHD?

Inattention

Adults see different signs of inattention in children with ADHD. An apparently special aspect of the disorder is the situational attention of children: the child can concentrate well if he or she is interested or motivated, while it has concentration problems when performing a boring, strenuous or repeated task. Research shows that children and adolescents with ADHD do indeed have more concentration problems than children with learning disabilities or normally developing children. Specific deficits have been identified, including a lack of selective attention: the ability to focus on relevant stimuli and not be distracted by irrelevant stimuli. Children with ADHD are more easily distracted if the task is boring or difficult or if irrelevant stimuli are new or striking. Children with ADHD also have deficits when it comes to attentional alerting (the ability to immediately focus on something important) and retained attention (staying focused on a task or stimulus for a longer period of time).

Hyperactivity

Children with ADHD are hyperactive. In general, motor hyperactivity and restlessness are more common in structured situations, where children have to sit still and regulate their behaviour, especially while they are only minimally endorsed for this.

Impulsivity

Another important aspect of ADHD is impulsiveness: a deficiency in inhibiting or controlling their own behaviour. Children with ADHD often do things without first thinking about it, such as interrupting others or displaying risky behaviour. Impulsivity can be measured with, among other things, the stop task. For example, two letters may appear on a screen, such as the letter X and the letter O. The child should only press the button when the letter X is visible on the screen and he or she hears a beep. Children with ADHD have a hard time performing this task.

Secondary characteristics of ADHD

In addition to the core problems of ADHD, children with ADHD experience secondary problems: problems in various areas of functioning. It should be noted, however, that most of the study results discussed below are based on children with the combined subtype of ADHD. It is therefore unclear to what extent these results can be applied to children with ADHD-I or ADHD-HI.

Children with ADHD-C may experience problems in the following areas:

• Motor skills : for example, clumsiness, delay in reaching motor milestones, poor sports performance, poor fine motor skills, difficulty in performing complex motor actions.
• Intelligence, academic functioning: somewhat lower than average performance on intelligence tests, specific learning limitations (for example in the area of ​​reading or arithmetic), low grades, cheating, skipping school.
• Executive functions: cognitive processes that are important in the regulation of goal-oriented behaviour and that are involved in planning and organizing actions. Examples are the working memory, verbal self-regulation, behavioural inhibition and motor control. Children with ADHD experience problems with executive functions, which has implications for their functioning in other areas.
• Adaptive Behaviour: Independence deficits, childish behaviour, more adult supervision required, difficulty in learning everyday skills, difficulty in implementing familiar skills (due to attention deficits and executive functions).
• Health: some studies indicate that children with ADHD are more likely to suffer from allergies and asthma, but the study findings are inconsistent.
• Sleep: for example, difficulty falling asleep, waking up at night, being able to sleep fewer hours and involuntary movements during sleep (for example, grinding teeth). Possibly sleeping problems are the result of comorbid problems, such as anxiety, or medication.
• Accidents: children with ADHD are more often involved in accidents than children without ADHD. This is possibly caused by inattention, impulsivity, motor coordination problems and aggressive behaviour.

What is the effect on social behaviour and relationships?

Children with ADHD also often have social problems. Limitations in social behaviour are often associated with two behavioural elements:

• Restless and intrusive behaviour: expressing itself, for example, by talking a lot and interrupting others.
• An aggressive, negative style of interaction manifests itself, for example, through physical and verbal aggression towards others.

Although this is not often recognized, inattention can also be related to social problems because it is associated with not listening, being easily distracted and a tendency towards anxious, shy and withdrawn behaviour.

There are various explanations for the social problems of children and adolescents with ADHD:

• Inadequate processing of social-emotional cues.
• Inability to display appropriate behaviour, especially if the individual is excited or irritated.
• Shortages in the ability to regulate and plan emotions and organize and shortages in the working memory.
• A positive self-bias with regard to their own behaviour and their own social and academic competence. Children with ADHD are often unaware of their negative influence on others, judge their relationships as extremely positive and overestimate the extent to which they are accepted and liked.

Many children with ADHD are rejected by peers. Children with only attention problems are often ignored. In addition, children with ADHD often have difficulty making and keeping friends. The child-teacher relationship and family relationships are also influenced by ADHD.

DSM subtypes

There are several issues related to the different subtypes of ADHD in the DSM. For example, only a few children are diagnosed with ADHD-HI. ADHD-HI may be an early stage of ADHD-C instead of a separate subtype. In other cases, ADHD-HI seems to be better regarded as ODD.

Some studies of the subtype -I have found a factor called a slow (sluggish) cognitive pace . This is characterized by daydreams, confusion and social withdrawal. However, these behaviours are not mentioned in the diagnostic criteria of the DSM.

Subtypes are considered valid if there are not only differences in symptoms, but also in other important characteristics. ADHD-I differs from ADHD-C in several respects. ADHD-I develops at a later age and girls with ADHD are more often diagnosed with ADHD-I than with other subtypes. In addition, ADHD-I is associated with fewer externalizing symptoms, but more with internalizing symptoms than ADHD-C. Inattentive children are rejected less often, but more often ignored by peers than children with ADHD-C. There is also evidence of differences in the genetic and neurobiological factors associated with both subtypes.

The validity of ADHD-I is nevertheless questioned. For example, no differences are found on tests of inattention and impulsiveness. In addition, prenatal smoking behaviour of the mother seems to be related to ADHD, regardless of the subtype. Such findings suggest that the subtypes do not differ from each other that much and that ADHD-I may be a milder form of ADHD-C.

Nigg has done family research in which it shows that children with ADHD-I do not have a family member with ADHD-C more often than control children, while children with ADHD-C tend to, more often, have a family member with ADHD-I. This suggests that some children with ADHD-I do form a separate subtype and that some children with ADHD-I actually have a milder form of ADHD-C.

A more general issue regarding the subtypes of ADHD has to do with the instability of the diagnosis. Children who are diagnosed with a certain subtype at a certain time often receive a different subtype at a different time. Although actual changes may occur, this is probably due to methodological factors.

ADHD-I is mainly associated with internalizing emotions. These children are passive and shy. Their brains may work differently than those of children with ADHD-C.

What are comorbid disorders?

Comorbidity is common in children with ADHD and in particular ADHD-C. Children with ADHD only seem to be the exception rather than the rule. ADHD often occurs with the following disorders:

• Learning disability: 15-40% of children with ADHD also have a learning disability. Although the relationship between ADHD and learning difficulties is not yet fully understood, there is some evidence that ADHD leads to reading problems rather than the other way around. In addition, inattention plays a greater role than hyperactivity-impulsivity. The comorbidity of ADHD and reading problems is largely explained by shared genetic influences.
• Externalizing disorders: relatively many children with ADHD develop ODD, and some of them subsequently develop CD.
• Internalizing disorders: 12-35% of children with ADHD have an anxiety disorder. These children are often less hyperactive and impulsive than children with ADHD alone. 25-30% of children with ADHD have MDD and 10-20% suffer from bipolar disorder. It is difficult to distinguish between mania and ADHD, because impulsivity and hyperactivity are symptoms of both disorders.

Epidemiology

The prevalence of ADHD can be estimated to vary from 3% to 7%. When looking at prevalence, a distinction must be made between clinically diagnosed ADHD and reporting of symptoms by parents and teachers. In the latter type, the prevalence is often higher and can be as high as 20%. This is partly explained because no criteria apply, such as the age of the onset of symptoms and interference with functioning.

The prevalence of ADHD appears to decrease in adolescence. However, this may also be due to the diagnostic criteria, which may not be appropriate for the way the disorder is expressed in adolescence. ADHD may be under-diagnosed in adolescence.

Boys are diagnosed with ADHD three times as often as girls. This is partly explained by a referral bias because boys exhibit more aggressive and antisocial behaviour. In addition, there is a bias in the diagnostic criteria to behaviour that occurs more often in men. In addition, girls are often diagnosed with ADHD on the basis of inattentive and disorganized behaviour, which is less noticeable than hyperactivity and impulsiveness.

ADHD occurs in all social classes but is sometimes associated with a lower socio-economic status. Finally, the prevalence of ADHD differs between different ethnic and cultural groups.

What is the developmental process?

Baby time and preschool years

In some cases ADHD has its origins in infancy, but the question is how ADHD is expressed so early. Behaviour can occur at preschool age that resembles ADHD symptoms, but little is known about this age group. ADHD may be the result of temperament tendencies, such as poor self-regulation and strongly approaching behaviour. Research is still being conducted into the distinction between early behaviours that are predictive of ADHD and normal misconduct by young children.

Childhood

Most children are diagnosed with ADHD between the ages of 6 and 12. This is partly due to the demands placed on children at school with regard to, among other things, behavioural regulation, such as sitting still and paying attention. Deviations from the norm thus will then stand out.

Adolescence

In many children, the primary symptoms, and especially hyperactive or impulsive behaviour, decrease in adolescence, making the ADHD diagnosis no longer applicable. Yet the disorder is often persistent. Two aspects of the manifestation of symptoms are remarkable. First of all, there is a high risk of heterotypic continuity of symptoms: the core symptoms can be expressed in a different way. Running around inactive during childhood, for example, turns into an inability to relax. Secondly, many children who no longer meet the diagnostic criteria exhibit more ADHD symptoms than peers who have never been diagnosed with ADHD.

Maturity

40-60% of individuals with ADHD still exhibit core symptoms and other problems such as problematic social relationships, drug use, negative self-image and antisocial behaviour.

Variation and prediction of outcomes

When studying the developmental course of ADHD, the general picture must be taken into consideration. First of all, the core symptoms, in particular hyperactivity and impulsivity, decrease with age. In addition, many secondary problems arise which can be persistent. Variables that can predict the outcomes of adolescents and adults are the age of ADHD, the severity of symptoms, the presence of behavioural problems, intelligence, adverse family circumstances, psychopathology in parents, parent-child interactions, parenting practices and genetic factors .

What are neuropsychological theories of ADHD?

Executive functions and inhibition

Children with ADHD have deficits in executive functions. In Barkley's model, reaction inhibition plays a central role in explaining hyperactivity and impulsivity in ADHD. Behavioural inhibition consists of three skills:

• The ability to inhibit 'prepotent' responses (responses likely to be validated or confirmed in the past).
• The ability to interrupt responses that prove to be ineffective.
• The ability to inhibit conflicting stimuli, so that the execution of executive functions is not disrupted (the ability to not get distracted).

These skills form the starting point for self-regulation. Behavioural regulation is made possible by the following executive functions:

• Non-verbal working memory allows the person to keep information 'on the backburner’, so that it can be used to check a subsequent reaction.
• Verbal working memory: internalization of speech. Enables the person to reflect mentally on rules and instructions that are internalized to guide behaviour.
• Self-regulation of affect, motivation and arousal: processes that enable the person to adjust emotions and motivation, such as reducing anger.
• Reconstitution: allows the person to analyse and synthesize (to divide and recombine non-verbal and verbal units), allowing him or her to construct new behaviours.

Sensitivity to rewards

Children with ADHD have an unusual sensitivity to rewards. This motivational problem is reflected in excessive reward-seeking behaviour and a reduced sensitivity to punishment. Children with ADHD have a marked preference for immediate over-deferred rewards, even if the immediate reward is smaller. A study has suggested that they have abnormal heart responses to rewards and punishment.

Processing of time and aversion to delay

Children with ADHD somehow always have a shortage of time, which is reflected in various tasks. In this way they underestimate how fast time goes. Processing time is important in controlling and adjusting behaviour and may be related to the problems that children with ADHD have with waiting and planning.

Some argue that children with ADHD have an aversion to procrastination, which is reflected in attempts to avoid procrastination. From this perspective, for children with ADHD an immediate reward has more to do with avoiding delay than with the reward itself. It is claimed that in situations where delay cannot be avoided, children pay attention to aspects of the environment, thereby speeding up the perception of time. For example, they will behave more busily.

Multiple paths

Several neuropsychological factors are probably involved in the development of ADHD. ADHD subtypes may exist based on differences in neuropsychological limitations. A dual path model has been proposed, with two independent paths that lead to the development of ADHD: one path is mediated by deficits in executive functions and the other path by aversion to delay. Both paths are characterized by different brain circuits. There is some evidence for this model. Recently the possibility has been investigated that the processing of time forms a third path. The findings support a three-path model and subtypes of neuropsychological disabilities.

Neurobiological abnormalities

Research shows that the brains of people with ADHD have different patterns. There are various brain structures that are related to ADHD, such as the frontal, parietal and temporal lobes, the corpus callosum, the thalamus and the cerebellum. In some structures there is a reduced brain volume. Deviations in the frontal and striatal areas and the cerebellum appear to play a major role in the core characteristics of ADHD and in many neuropsychological deficits associated with ADHD. In addition, there is underactivity of the brain, which can be derived from, among other things, a lower blood flow, reduced glucose consumption and slow brain waves in children with ADHD. ADHD is also associated with abnormalities in neurotransmitter systems, such as dopamine and norepinephrine: neurotransmitters involved in executive functions, motivation and reward. The question is whether the brain abnormalities in ADHD the result of abnormalities of normal development are or of delayed development. There is some evidence that there is a development delay.

Aetiology

Genetic factors

There is strong evidence for the influence of genetic factors on ADHD. For example, family members of children with ADHD have an increased risk of psychopathology. About 10 to 35% of the immediate family members of a child with ADHD also have ADHD themselves. There even is a small component of it visible in the brains of brothers and sisters of a child with ADHD, although they do not have ADHD. Twin research shows that the hereditary component of ADHD is 0.80.

Prenatal influences and birth complications

The research findings regarding the relationship between prenatal influences and ADHD are inconsistent. Prenatal smoking and alcohol consumption are probably risk factors. Premature births and low birth weights are also risk factors.

Diet and lead

Eating patterns do not play a role in the cause of ADHD. Lead exposure is related to ADHD and deficits in various executive functions. However, the influence of lead on ADHD is probably small.

Psychosocial factors

Few researchers believe that psychosocial factors are a primary cause of ADHD. Psychosocial factors probably have an influence on the nature, severity and continuity of symptoms and on additional problems. Various family factors, such as stress, family conflicts and parental psychopathology, are associated with ADHD. There is evidence that ADHD in children can influence parenting behaviour and that parenting behaviour can influence the nature and development of ADHD. However, research results on family factors are contradictory and it is not clear how these factors interact with genetic predisposition. The behaviour of teachers can play a role in the manifestation and outcomes of ADHD.

The development of ADHD

A model that shows the development of ADHD states that various risk genes (possibly in interaction with prenatal and perinatal influences) lead to brain abnormality and associated neuropsychological deficits. Different paths can lead to ADHD. This model shows three hypothetical paths. Postnatal environmental influences play an important role in these paths. Secondary influences, such as a diet or exposure to toxic substances, can have a direct influence on brain processes. Tertiary influences, such as a negative upbringing, can mediate or moderate the outcomes through social interaction. This entire process can not only lead to ADHD, but also to comorbid disorders.

How do you assess and treat it?

Various aspects of ADHD provide guidelines for the assessment:

• ADHD is a biopsychosocial disorder, so attention must be paid to both biological and psychosocial factors in the assessment.
• ADHD is a developmental disorder, so a development history must be taken, and the assessment must be adjusted to the developmental level of the child.
• ADHD can be expressed in different ways in different settings, so situation-specific information must be collected.
• ADHD is often accompanied by other disorders, so the assessment must distinguish between ADHD and other disorders.

The interview is a commonly used assessment method. ADHD assessment often takes place at a young age, so parents are important informants. It is important to pay attention to family relationships and specific parent-child interactions, as this has implications for treatment. The child itself must also be interviewed. In addition, interviews with teachers are valuable for obtaining information about problems at school.

In addition to interviews, one can also make use of questionnaires and observations. Other aspects of functioning can also be assessed, such as general intelligence, adaptive behaviour and academic functioning.

Interventions

Prevention

The most effective way to reduce prevalence is to focus on treating the early symptoms of ADHD and on reducing secondary problems (for example, reducing social problems through social skills training).

Pharmacological treatment

In most cases, children with ADHD are treated with medication, behavioural therapy, or a combination of both. Prescribing stimulants often happens. These drugs affect the neurotransmitters dopamine and norepinephrine. There are different variants: a variant with a slow and longer-lasting effect that only needs to be taken once a day and a variant with a fast, but shorter effect that needs to be taken more often. The slow variant is prescribed more often. Medication helps to reduce the primary problems of ADHD. About 75% of children with ADHD have fewer concentration problems and become less hyperactive and impulsive after using stimulants. Aggressive and disobedient behaviour is also reduced. In addition, medication has some effect on academic skills.

Medication is less effective in the pre-school period and adolescence than in the primary school period. Yet there is much evidence for its effectiveness at different ages and in different settings.

One of the concerns about medication concerns the side effects, such as sleeping problems, loss of appetite, stomach pain and headache. These are mild to moderate side effects that often disappear in two to three weeks. The use of stimulant drugs also appears to be hampering the growth of a child. However, this effect is small. In addition, some fear that the use of stimulants is a risk factor for drug use and drug abuse. However, it is not clear whether this is a cause-effect relationship. For example, it is possible that the link can be explained by a shared genetic influence. Some scientists believe that stimulants are prescribed far too soon to children and that it appears to be used by some parents and schools as a quick and easy solution.

Behavioural therapy

Behavioural therapy focuses on the primary symptoms of ADHD and on improving functioning in various areas such as social relationships and school performance. Many treatments are performed at school or at home.

Parent training is a method to teach parents how to deal with their child with ADHD. For example, parents learn effective parenting skills. Parent training is mainly used for children between four and twelve years of age and can partially reduce the symptoms of ADHD in children or at least the expression of them.

It is also possible to conduct behavioural therapy at school. In that case, the teacher uses methods such as timeouts and point systems. It also appears that children with different types of ADHD benefit from different strategies from their teachers. Children with ADHD-I, for example, mainly benefit from a teacher who encourages slow work in the classroom. Therapy should focus on problems of individual children. Some children mainly have organizational difficulties and must be taught skills to keep their table tidy. Other children mainly have social deficits and need to improve their social skills. In addition, the therapy must be adjusted to the developmental level of the child. For example, young children should receive help with basic skills such as arithmetic, while older children need to be supervised in other academic areas. Problem situations (such as breaks at school) must also be addressed.

The structure and organization of the classroom and learning tasks are important for children with ADHD. With regard to the class, for example, it can be effective to have the child sit close to the teacher, so that the teacher can supervise the child more closely. With regard to learning tasks, among other things, it is important to keep the tasks short and to introduce variation in the way the task is offered. In general, knowledge, ideas, attitudes, flexibility, tolerance and the interaction style of the teacher are important factors in determining the effectiveness of behavioural therapy at school.

Multimodal treatment

Due to the advantages and disadvantages of both pharmacological and behavioural treatment, both are often combined in a multimodal treatment. The Multimodal Treatment Assessment Study (MTA) examines the long-term effects of various treatments. For this, four groups of children are looked at:

• children who only receive medication
• children who only receive behavioural therapy
• children who receive both medication and behavioural therapy
• children who receive other (government-supported) community treatments

The research results show that medication and combined treatment are the most effective. The research findings are nevertheless complex. For example, children with combined treatment exhibit fewer internalizing and externalizing symptoms after the examination. For children with both ADHD and an anxiety disorder, behavioural therapy, on the other hand, is just as effective as medication or a combination of both. In addition, some outcomes are moderated by the social class. Children from families with a higher level of education benefit relatively more from a combination of behavioural therapy and medication. In the longer term, some research results weaken a little. This confirms that the treatment of ADHD must be maintained over time. In the longer term, some research results may weaken a little. This confirms that the treatment of ADHD must be maintained over time.