ADHD has been recognised in children for well over a century with the first medical description of ADHD credited to Still, a British Paediatrician, in 1902 (Lancet: Gaulstonian lectures). The first recorded treatment of ADHD in children was with benzedrine by Charles Bradley in 1937 and in 1963 methylphenidate was first used, again in children. Assessment and treatment of children and adolescents with ADHD is now routine practice worldwide, including in Ireland (HSE 2013).
The first study of its persistence into adulthood was carried out in 1976 (Wood) and it showed that, like children, adults had a similar pattern of core symptoms; associated impairments of equivalent functional domains; a similar pattern of co-morbidity; a similar response to stimulant medication and similar cognitive performance measures. Despite these findings and subsequent evidence of the number of adolescents who continue to experience distressing and impairing symptoms into adulthood (Barkley 2002, Faraone 2006), there was little in the way of service response. So much so that in 2003, the British Journal of Psychiatry published an invited debate on “ADHD is best understood in a cultural concept”. The paper did not conclude for or against this proposition (Timini 2003) but did state that broad social influences probably contribute to the recognition of the disorder rather than its prevalence. Adding these do not amount to a social construction of disorder but in the UK at least worked against recognition of a treatable risk. Philip Asherson in his pivotal paper (Asherson 2005) described the effects of unrecognised and untreated ADHD in adults.
- the distress of symptoms secondary to the core features of inattention, hyperactivity and impulsivity on the person and other people around them, including family and friends.
- impaired ability to function at work and in academic settings.
- problems in sustaining stable relationships as a consequence of volatile moods, antisocial behaviour and drug and alcohol misuse.
- the effects of comorbid mental illness, especially anxiety and depression.
At around the same time an Irish study examined the diagnosis and management of attention deficit hyperactivity disorder in children and adults with and without learning disability. This took the form of a postal questionnaire to 302 Consultant Psychiatrists listed in the Irish Medical Directory in 2003. The response rate from adults psychiatrists (25%) was much lower than from child psychiatrists (67%) and learning disability psychiatrists (75%). Of note the child psychiatrists were significantly more confident (P<0.05) about diagnosing ADHD in children with and without learning disability than psychiatrists working with adults (Buckley 2006).
The availability of just one public service in Sligo/Leitrim in 2018 indicates little has changed in the intervening years (Adamis 2017).
From this account it is clear that it took some time for ADHD to be accepted as a diagnostic entity in children. Similarly, there has been some resistance to its acceptance as a valid diagnosis in adults, despite its recognition as such by WHO (1996), the National Institute for Clinical Effectiveness (2008), Royal College of Psychiatrists, American Psychiatric Association, Royal College of Australia and New Zealand and the Canadian Psychiatric Association.
Adult ADHD was, and still occasionally is, perceived as a dubious diagnosis used by patients seeking stimulants for nefarious purposes (Geffen 2018). The symptoms, like those of other mental disorders such as major depression and post traumatic disorders in the past, suffer from being on a continuum. This leads to accusations of medicalising normal experience.
However, there is now a wealth of evidence accumulating that persistence of syndromal ADHD into adulthood does occur to a significant degree (Faraone 2006) with poorer functioning in all domains (Agnew-Blais 2018) and that it responds to integrated pharmacological and psychotherapeutic intervention thereby reducing disability and improving quality of life (Vidal-Estrada 2012, Jensen 2016, Morgensterns 2016, De Crescenzo 2017, Lopez-Pinar 2018).
A common reason given for adult mental health services not providing treatment for ADHD in adults is that it is a neurodevelopmental disorder (ICD 10, 1996, Geffen 2018). However, neurodevelopmental disorders are now considered to include not only ADHD but also schirophrenia and both bipolar disorder and major depressive disorder when associated with psychosis (Mullins 2013). Common to each is evidence of cognitive dysfunction with the pre-frontal cortex in particular involved (Etkin 2013).
This takes the form of executive dysfunction resulting in problems with working memory, flexibility and inhibitory functions, thereby impairing goal directed behaviour (Miller 2001). It is now central to our understanding of disability in psychiatric illness (Geffen 2018).
Another question that arises is whether services for adults with ADHD should be combined with those for adults with autistic spectrum disorder (ASD) since both are commonly classified as neurodevelopmental disorders. Notwithstanding the latter, a key difference is that there is effective treatment available for the core symptoms of ADHD but not for those in ASD.
The prevalence of ADHD in adults is significant with an estimate of 3.4% (range 1.2% - 7.3%) indicated by Fayyad (2007). A meta-regression analysis of six prevalence studies of ADHD found a pooled prevalence of 2.5% (Simon 2009).
However, it is important to distinguish between those with symptoms, described as in partial remission, from those meeting all diagnostic criteria. The latter also have impairment in at least two functional domains and their prevalence is 1.5% in the adult population (Faraone 2006).
A study of ADHD in a variety of settings in the United Kingdom showed a rate of 15.3% in non-psychotic adults attending secondary mental health care (Murphy 2013). Other findings in the same study were 2.5% in the overall adult population and 25% in the prison population.
Deberdt’s study on the prevalence of ADHD in adults (without psychosis) attending outpatient settings found an overall prevalence of 15.3% using the Diagnostic Interview for Adult ADHD (DIVA 2010) and based on DSM V criteria. The study involved 1,986 adults of whom 1,079 screened positive on the 6 item Adult Self-Report Scale (ASRS), (Kessler 2005), a screening tool. Of the 804 who completed the DIVA, 349 were found to have ADHD.
The majority had the combined type (63%). More women were first diagnosed as having ADHD by this study (60% v. 48%) with an overall prevalence rate of 14% in woman compared to 21% in men. The study concluded that ADHD is present in a substantial proportion of non-psychotic patients seeking psychiatric help. Compared to other people attending psychiatric outpatients they are amongst the most impaired. The authors recommended systematic screening. However, they also recommended using additional screening criteria that would improve the specificity of existing tools with minimal loss of sensitivity.
A study by Rao (2011) of current attenders in four psychiatric outpatient clinics in North East England, excluding those with organic disorders and acutely ill, found a prevalence of 22%. The diagnoses were clinically based on DSM IV criteria supplemented by the British Association of Psycho-pharmacology recommendations. The authors concluded that the presence of co-morbid ADHD offers other avenues of therapeutic intervention that may be helpful to these patients.
The gender differences in prevalence change from 4:1 males to females in childhood to 2:1 in young adults (Bramham 2012). This might represent an underdiagnosis in girls who are more likely to have the inattentive form of ADHD. Also, with increasing age, the greatest improvement is in symptoms of impulsivity and hyperactivity. A combination of both factors probably contributes (Young and Bramham 2007).
A longitudinal study in New Zealand suggested there may be an adult onset form of ADHD (Moffitt 2015).
However, a recent American study based on repeated comprehensive assessments refutes this (Sibley 2017). It states previous reports are limited by relying on screening instruments only to assess for ADHD, not considering alternative diagnoses or not obtaining complete psychiatric histories. Careful clinical assessment, including a good collateral history from a person who has known the patient as a child, is essential.
Two Irish studies, one urban and one rural, both including people attending adult outpatient clinics found over 20% screened positive for ADHD symptoms (Syed, 2010; Adamis, 2017). The Syed study in an urban area of North Dublin used the six item Adult Self Report Scale VI.I (Kessler 2005). 243 of 264 patients approached completed the questionnaire of whom 58 screened positive for ADHD symptoms. There was no difference in those who screened positive from those who did not in age (average 42 years), duration of clinic attendance (6-7 years) and substance misuse. Those screening positive were twice as likely to have been in trouble with the law (21% versus 10%) and not to have completed secondary education (56% versus 38%). The male:female ratio in those screening positive was 2:1.
The Adamis study examined the largely rural population in counties Sligo and Leitrim with a total population of 109,000 people. Adult attenders of all mental health outpatient clinics aged 18-64 years were asked to complete two questionnaires: the ASRS Parts A (6 questions) and Part B (12 questions) (Kessler 2005) and the Wender Utah Rating Scale (WURS) shorter 25 question format (Ward 1993). Of 760 eligible patients, 634 completed both questionnaires. 215 (33.9%) screened positive for possible childhood ADHD on the WURS and 219 (34.5%) screened positive for possible current ADHD on the ASRS.
This study applied the more stringent criteria of requiring positive screening on both scales. It indicated 131 people (20.7%) might have ADHD of whom only 3 had a diagnosis of childhood ADHD. There was no difference in gender ratio (1:1), marital status, occupation (with high levels of unemployment in both of over 45%) or education in the groups of positive and negative screeners. There was a difference in age (average of 41.3 years in non cases and 36.7 years in possible cases) and in house ownership (51% v. 35%). However, the latter might be explained by age alone. Adamis is now carrying out full assessments on those screening positive for possible ADHD.
The aetiology of ADHD is an interplay between genetic and environmental factors. Evidence for the genetic aetiology includes:
- 80% concordance in identical twins (Rietveld 2003).
- Faraone’s meta-analysing of 20 twin studies estimated the heritability of ADHD to be .76 (2005).
- Parents with ADHD may have a 35-50% chance of having a child with ADHD and 25% of children with ADHD may have a parent with the condition (Faraone 2001).
- Molecular genetic studies suggest several genes involved in the regulation of neurotransmitter function interact to produce a disorder of neurotransmitter function associated specifically with dysregulation, rather than a deficit, of dopamine and noradrenaline. Underfunctioning of these two transmitters is thought to result in the clinical symptoms of inattention, hyperactivity and impulsivity (Thapar 2013).
Methylphenidate, the main pharmacological treatment for ADHD, increases the levels of both these neurotransmitters (Arnstein 2006) supporting this hypothesis.
A recent paper in the Lancet (Hoogman 2017) provides the strongest neurobiological evidence for ADHD. This reports a cross-sectional mega-analysis of subcortical brain volume differences in participants with ADHD, both children and adults. It used MRI data from the international ENIGMA ADHD workshop group (9 countries in total: 1,713 participants with ADHD and 1,529 controls). The volume of certain subcortical structures (accumbens, amygdata, caudate, putamen) and of the hippocampus as well as overall intra-cranial volume were smaller in individuals with ADHD. The differences decreased with increasing age supporting the view that ADHD is a neurobiologic condition caused by delayed maturation. The study also found the changes in brain volume were not due to stimulant medication or comorbid conditions. The largest effect was found in the amygdala. This was considered important because of the prominence of emotional dysregulation in ADHD.
Possible environmental associations with ADHD
- Perinatal factors such as maternal smoking and alcohol use (Linnet 2003; Das Banerjee 2007)
- Perinatal trauma particularly hypoxia (Lou 2004)
- Acquired neurological disorders e.g. encephalitis (Chou 2015) and stroke (Max 2003)
- Severe adversity in childhood as evidenced by increase rates of ADHD in some children adopted from Romanian orphanages (Kreppner 2001, Kennedy 2016)
Thus the aetiology of ADHD is multi-factorial involving the interplay of multiple genetic, neurobiological and environmental factors, including psycho-social adversity (NICE 2013). At its simplest, it is thought that disrupted neurotransmitter function results in the symptoms of ADHD. The underlying pathophysiology is poorly understood.
Large scale genetic studies have shown that it is a complex genetic disorder with multiple risk genes of small effect and it is likely that gene-environment interactions increase susceptibility to the development of the disorder. Neuro-imaging studies have demonstrated brain abnormalities with differences decreasing with age supporting the view that ADHD is a neurologic condition caused in part by delayed maturation.
This section gives an overview on the diagnosis of ADHD in adults which informs the later section on diagnosis in chapter 7.
Asherson (2005) described the non-recognition of ADHD by adult mental health services leading to people being misdiagnosed and treated for other conditions. These include atypical depression, mixed affective disorders, cyclothymia and borderline/emotionally unstable personality disorders. This can be attributed to a combination of the prominent mood lability seen in adults with ADHD together with the more subtle expression of hyperactivity and impulsivity in adults. Specifically age related evolution of symptoms in childhood of hyperactivity and impulsiveness often diminish in adulthood with inattention, disorganisation and impaired behaviours secondary to executive dysfunction becoming more obvious (Kooij 2010). Where antisocial behaviour features prominently, a misdiagnosis of borderline/emotionally unstable personality disorder is likely to occur (Kooij 2010; Ginsberg 2014).
The NICE Guidelines on the diagnosis and management of ADHD (2008) state that symptoms of ADHD are distributed throughout the population and vary in severity, only those with significant impairment meet criteria for a diagnosis of ADHD. These guidelines include adults and internationally have been pivotal in guiding service provision. Likewise the European Consensus Statement on diagnosis and treatment of adult ADHD (Kooij 2010) aims to increase awareness of the disorder thereby improving knowledge and care of adults with ADHD across Europe. Its purpose is primarily to support clinicians by providing research evidence and clinical experience from the eighteen European countries participating in this Consensus Statement. It identified ADHD in adults as an impairing lifelong condition which is underdiagnosed in most European countries (including Ireland) leading to impaired quality of life following ineffective treatment thereby resulting in on-going distress and impairment.
Long term follow up studies of adults with ADHD document fewer social relationships and friends, higher rates of academic failure, lower occupational status, increased substance misuse (both alcohol and drugs), increased number of accidents (especially driving) and offending behaviour (Kesler 2005; Murphy 1996; Barkley 2007; Barkley 2002; Able 2007; Biederman 2006). Not surprisingly, untreated adult ADHD has a higher cost of illness in economic terms (Adamou 2010).
Asherson, in his seminal paper of 2005, concluded that any psychiatrist using standard assessment procedures could perform clinical evaluations of adults with possible ADHD as it has a highly characteristic psychopathology, runs a chronic persistent course (from childhood) and, importantly, responds well to multimodal treatment Diagnosis is made by thorough clinical assessment. There is no psychological testing or rating scale that can be used instead.
International Medical Classification Systems
The two main classification systems used for diagnosing ADHD are ICD 10 (1993) and DSM 5 (2013).
ICD 10, developed by the World Health Organisation refers to ADHD as hyperkinetic disorder (HKD), a term widely used in Europe and included in the European Clinical Guidelines developed by the European Network for Hyperkinetic Disorders (EUNETHYDIS).
The DSM V classification system for ADHD is published by the American Psychiatric Association and is used in the USA and the rest of the world. It replaced DSM IV in 2013 and the main difference is the requirement for impairment in two functional domains. This is also required in ICD 10.
In both classification systems, the features of ADHD are similar but ICD 10 requires that all three features (inattention, hyperactivity and impulsiveness) are present whereas DSM V diagnostic criteria require a pattern of inattention and/or hyperactivity-impulsivity (combined, predominantly inattention or predominantly hyperactive-impulsive presentations).
This Model of Care recommends diagnosis is made using the Diagnostic Interview for Adult ADHD (DIVA-5) (Kooij 2019) based on DSM V criteria.
2.5 National Policy
A Vision for Change (AVFC: 2006), Ireland’s national policy for mental health services until very recently, refers to children with ADHD being assessed and treated by Child and Adolescent Mental Health Services. However, it was written in 2006 and in the intervening years there have been considerable advances in recognising the condition is more likely than not to persist into adulthood, continues to cause distress and impairment and effective treatment is available. The ethos of AFVC informs the principles and design of the service recommended by this Clinical Programme.
- Involvement of service users in every aspect of service development.
- Well trained and staffed community based multidisciplinary teams.
- Services across the (adult) lifespan.
- A range of relevant medical, psychological and social therapies.
- A recovery orientation informing every aspect of service delivery, specifically with service users as partners in their own care.
- Close links between the mental health (Adult ADHD) service, primary care and voluntary groups.
- Organised nationally as discrete catchment areas of between 250,000 – 400,000.
- Clear local and national governance structure.
- Meaningful evaluation of (ADHD) services supported by an appropriate information dataset based on (ADHD specific) national data.
- Clear plan for required (ADHD) education all overseen by an (ADHD) implementation group.
The Evidence Review to inform parameters for a refresh of A Vision for Change (DOH 2017) referred to the use in the Netherlands of multi-disciplinary guides on mental health including one on ADHD in Adults. It also described the use of Breakthrough Quality Collaboratives (QICS). These are quality improvement profiles based on multi-faceted strategies to support the implementation of these guidelines. The key features, applicable to ADHD for instance, are:
- a focus on ADHD in recognition of the gap between current and best practice
- clinical experts who provide ideas and support for improvement
- participation of multidisciplinary teams from multiple sites
- a model for improvement (setting targets, collecting data and testing changes)
- a collaborative process with a series of structured activities within a given timeframe (Forti 2014).
This is similar to the process used in this clinical programme.
Sharing the Vision (DOH 2020), the new national policy on mental health, states ADHD in adults is an under recognised and under-diagnosed lifelong condition; one that leads to impaired quality of life, results in on-going distress and is often associated with inappropriate treatment interventions. In Sharing the Vision’s Implementation Plan, Action 53 requires the phased implementation and evaluation of appropriate service responses to support adults with ADHD be developed and resourced in line with the National Clinical Programme for Adults with ADHD.
Sláintecare (Government of Ireland, 2017) now the national policy on health care in general with its emphasis on integrated care is very relevant. It describes integrated care based on the patient being paramount. Its key components are a public service, timely access, appropriate care pathways, seamless transition backed up by full patient records and information.