Global burden of mental disorders in children and young people

Globally, the prevalence of mental health disorders in children and young people has contributed to the increasing burden of these disorders. One in five children in England has a probable mental health disorder, and this increases to one in four among 17–19-year-olds.^{Reference Mathews, Ford, White, Ukoumunne and Newlove-Delgado1} Mental health disorders in children and young people cause significant distress and can affect multiple areas of functioning (e.g. education, family life, peer relationships) and physical health, all of which may have implications for individual developmental trajectories. Around half of children and young people diagnosed with mental health disorders will have ongoing difficulties in adulthood.^{Reference Schlack, Peerenboom, Neuperdt, Junker and Beyer2}

Rare mental health disorders

Commonly occurring mental health disorders have been well studied in terms of epidemiology, presentation, risk factors and management. However, rare or uncommon mental health disorders (defined as those that occur in fewer than one in 2000 individuals)³ cannot be well studied using community research. Some examples of these rare disorders include childhood eating disorders, paediatric onset bipolar disorder and childhood conversion disorder. Classification of disorders is constantly evolving, and any changes may lead to the inclusion of new, possibly rare, disorders in the classification systems which could be studied with the use of surveillance methodology. Although rare, these disorders can have a significant impact on children, young people and their families, as well as on mental health resources. The low numbers of these rare disorders in the population often cause delays in timely recognition and management.^{Reference Spencer-Tansley, Meade, Ali, Simpson and Hunter4} To study these disorders in detail and to generate scientific literature for clinicians, alternative methods of identification are needed.

Surveillance epidemiology

Active surveillance is an established method of generating accurate and timely data on rare health conditions and events which are difficult to identify using conventional methods. Although it requires more resources than conventional approaches, this method is likely not to miss any cases and provides more comprehensive and valid data regarding the condition under study; this is particularly important when studying rare conditions.^{Reference Nsubuga, White, Thacker, Anderson, Blount, Broome, Jamison, Breman, Measham, Alleyne, Claeson and Evans5} Rare paediatric disorders and events have been studied by the British Paediatric Surveillance Unit (BPSU) since the 1980s. The BPSU has provided useful data that has influenced vaccine and national screening policies, clinical research and practice on the ground. The BPSU was also instrumental in encouraging the development of similar surveillance systems across the globe.^{Reference Knowles, Friend, Lynn, Mitchell, Michie and Ihekweazu6} This paved the way for the establishment of the Child and Adolescent Psychiatry Surveillance System (CAPSS; https://www.rcpsych.ac.uk/improving-care/ccqi/research-and-evaluation/current-research/capss). This article summarises how CAPSS was developed, together with key studies that have used the system and their impact, to make the case for development of a wider international surveillance unit for child and adolescent psychiatry.

Development of CAPSS

In 2005, a pilot system for CAPSS was initiated to study early-onset eating disorders. The response to this study was promising, with more than 95% of consultants in child and adolescent psychiatry (CCAPs) supporting the need for the system and agreeing to continue to contribute to the surveillance. This enthusiasm from clinicians about a system for surveillance of rare child and adolescent mental health disorders led to CAPSS being officially established in 2009.^{Reference Price, McWilliams and Warrilow7} CAPSS, which is hosted by the Royal College of Psychiatrists, aims to:

1. (a) facilitate epidemiological surveillance and research into rare child and adolescent mental health disorders and events;

2. (b) increase awareness among the medical profession and the public about these disorders and events, as well as their impact on children and adolescents;

3. (c) enable psychiatrists to participate in surveillance of such conditions;

4. (d) inform clinical strategy and public health policy;

5. (e) respond in a timely manner to clinical and public health concerns.

Planning and execution of the studies

CAPSS maintains a database of CCAPs working across the UK and Republic of Ireland. Researchers wishing to use the system submit proposals to the CAPSS executive committee for review. Once the proposal has been approved, researchers seek relevant ethics and governance clearances. An electronic reporting card with case definitions for all the disorders currently under study is emailed to all the CCAPs in the database each month. CAPSS informs the researchers of any notifications so that they can send out an initial questionnaire to establish caseness and, where relevant, follow-up questionnaires.^{Reference Price, McWilliams and Warrilow7}

Impact of CAPSS studies

The data gathered from the study on early-onset eating disorders have highlighted the need for a developmental framework for diagnosis which is reflected in the DSM-5.^{Reference Nicholls, Lynn and Viner8} This study has also encouraged more liaison between paediatricians and psychiatrists, which is critical to safe and effective clinical care. The incidence rates from the study on narrow-phenotype paediatric bipolar disorder provided information about the need for specialist services for this population.^{Reference Sharma, Neely, Camilleri, James, Grunze and Le Couteur9} Studies on transitioning care for attention-deficit hyperactivity disorder to adult services, gender dysphoria and childhood disintegrative disorder have also been completed and have provided insights for planning of service provision.^{Reference Price, McWilliams and Warrilow7} The most recent study on avoidant/restrictive food intake disorder (ARFID) was the largest to date. The incidence rates reported by the study indicated that ARFID may not be as rare as it was thought to be, and that it may require the development of specific clinical pathways.^{Reference Sanchez-Cerezo, Neale, Hudson, Lynn, Julius and Nicholls10} Details of the studies completed using CAPSS are provided in Table 1.

Table 1 CAPSS studies to date and key findings

ADHD, attention-deficit hyperactivity disorder; ARFID, avoidant/restrictive food intake disorder; BPSU, British Paediatric Surveillance Unit; CAMHS, child and adolescent mental health services; CAPSS, Child and Adolescent Psychiatry Surveillance System; LCA, latent class analysis; NPBD, narrow phenotype bipolar disorder.

Challenges and way forward

Despite promising results from the studies, CAPSS is not without challenges. It has been noted from surveys that patients with certain child and adolescent psychiatry conditions present to community paediatricians rather than CCAPs;^{Reference Ayyash, Ogundele, Lynn, Schumm and Ani11} examples include neurodevelopmental disorders, psychiatric manifestations of neurological conditions and emotional difficulties, especially in those under 5 years old. Individuals with some of the emotional disorders also initially present to general practitioners.

Within child and adolescent mental health services (CAMHS), the nature of involvement of child and adolescent psychiatrists in different clinical scenarios varies considerably.^{Reference Schumm and Morton12} Different CAMHS have different referral criteria, and the accepted referrals are distributed among different clinical pathways that may or may not include input from a CCAP. There are also child and adolescent psychiatrists within the teams who are trainees or specialist/associate grades and do not currently report to CAPSS. There is a need to keep in mind the possibility of cases being missed from surveillance and to consider strategies to prevent this. Finally, the development of such a process presupposes the existence of a mental health system which allows contact and coordination of all specialists within a region or country.

As well as the challenges described above, a major limitation of the current system is the geographical restriction in gathering of the data. This, combined with the innate rarity of the disorders being studied, raises the probability of insufficient data being collected. Moreover, without data from different countries and cultures, the cross-cultural generalisability of data is limited.

The need for a global network for surveillance in child and adolescent psychiatric disorders

The BPSU has set an example globally and led to the development of 12 other paediatric surveillance systems around the world. These have now collaborated to form the International Network of Paediatric Surveillance Units, which covers over 50 million children and has studied more than 150 rare disorders. With growing awareness of child mental health disorders across the globe, CAPSS can pave the way for the establishment of a similar international system of surveillance.

Any such system and the studies using it would need to acknowledge that some mental health disorders have strong cultural influences, and so clinical presentations, diagnostic thresholds and perceptions about the disorders may vary. Keeping this surveillance active in different populations across the globe will add to existing knowledge and understanding of these uncommon disorders and events. This will in turn help in developing better frameworks for the identification and management for these disorders and events. It will also facilitate the sharing of ideas regarding current methodology, ethics, the most appropriate means of evaluating units and their potential applications. Overall, this surveillance system may improve the knowledge of child psychiatrists about rare disorders and lead to improved diagnostic validity for these disorders and the development of treatment guidelines.