This study was funded by Shire, now part of Takeda
In Sweden, it is reported that 2.7% of all psychiatric diagnoses in adults are attributed to ADHD. Although awareness of ADHD in Nordic countries (including Sweden) appears to be increasing, globally it is still considered that the condition is largely underdiagnosed, with <20% of patients formally diagnosed with ADHD. ADHD in adults is an important health condition associated with increased use of healthcare services, unemployment and comorbid psychiatric disorders. An overview of the prevalence and treatment of ADHD in Sweden is useful both to inform clinicians and to allow adequate resource planning for managing patients in the future. This study sought to determine the overall prevalence of ADHD in Swedish adults between 2006 and 2011, and the incidence of newly diagnosed ADHD between 2007 and 2011 in this same population, and finally to assess the pharmacological treatments used and any psychiatric comorbidities reported.
This retrospective, longitudinal, observational study utilised two national population-based registers, the National Patient Register (NPR) and the Prescribed Drug Register (PDR).* Data were obtained from adults (aged ≥18 years) with a diagnosis of ADHD or hyperkinetic disorder (defined by the International Statistical Classification of Diseases and Related Health Problems, 10th Revision) and included age, gender, psychiatric comorbid diagnoses† and prescribed ADHD medications.‡ A cross-sectional dataset covering 1 January 2006 to 31 December 2011 was created to determine the prevalence of diagnosed ADHD. A longitudinal dataset was created, including individuals from 1 January 2007 to determine the rate of newly diagnosed adult ADHD and patterns of pharmacotherapy use. For individuals to be included in the longitudinal dataset, they must have had a defined ADHD diagnosis, during which no ADHD medication was dispensed 12 months prior to their appearance in the NPR.
Analysis of these datasets showed:
- The cross-sectional dataset included 44,364 individuals registered with a diagnosis of ADHD. The prevalence of diagnosed ADHD increased from 4149 individuals (0.58 per 1000) in 2006 to 26,820 individuals (3.54 per 1000) in 2011. The mean age increased from 30.8 (standard deviation [SD] 10.8) years to 31.7 (SD 11.6) years from 2006 to 2011, and the proportion of males decreased from 62.5% to 55.2% over the same period.
- The longitudinal dataset included 24,921 adults newly diagnosed with ADHD. The incidence of newly diagnosed ADHD increased from 2809 (0.39 per 1000) in 2007 to 6816 individuals (0.9 per 1000) in 2011. The mean age at new diagnosis increased from 31.4 (SD 10.7) years to 32.4 (SD 11.9) years, and the proportion of males decreased from 60.3% to 53.1% over the same period.
- In the cross-sectional dataset, 52.6% of individuals registered with a diagnosis of ADHD, and 54.0% of those newly diagnosed in the longitudinal dataset had ≥1 psychiatric comorbidity during the study period, with anxiety, substance-use disorders and depression representing those most commonly reported, whereas the least commonly reported in either dataset were impulse-control disorder and oppositional defiant disorder.
- Of all individuals diagnosed with ADHD in the cross-sectional dataset, 78.9% (65.7% of those newly diagnosed in the longitudinal dataset) received medication for ADHD during the study period, with osmotic release oral system methylphenidate representing the most frequently prescribed first-line ADHD medication. Of those newly diagnosed with ADHD, 35.3% received ≥1 add-on medication for ADHD.
- Concomitant treatment with anxiolytics, hypnotics and selective serotonin reuptake inhibitors had been dispensed in 22.5%, 20.5% and 18.5% of individuals with ADHD, respectively; however, concomitant use of antipsychotics (12.8%), serotonin-noradrenaline reuptake inhibitors (9.5%), non-selective antidepressants (3.0%) and other antidepressants (12.2%) was less frequent.
As with all studies which utilise administrative databases, the study had some limitations, including the fact that this study used information from hospital and outpatient administrative data, which may contain errors. In addition, the coverage of the NPR database is estimated to be ~75%, leaving 25% of all visits unaccounted for. The authors also noted that the high rate of individuals prescribed ADHD medication could be a result of doctors only recording a diagnosis once pharmacotherapy had been deemed appropriate. Additionally, the definition of ‘newly diagnosed’ could also have included patients diagnosed or treated with ADHD medication prior to 2006 who reappeared during the study period.
This study provided an estimated prevalence and incidence of ADHD in Sweden, along additional information on psychiatric comorbidities and subsequent treatment patterns. The data show an increase in ADHD diagnoses over time in Sweden, the majority of which were treated pharmacologically with ≥1 ADHD medication. The authors suggested that the high rates of concomitant medications indicate that current ADHD treatments are not sufficient in addressing all symptoms. The authors concluded that an increase in future resources for management of ADHD in adults will be required if the rate of diagnosis continues to increase.
Read more about the prevalence and incidence of adult ADHD in Sweden here
*The NPR covers 75% of psychiatric outpatient care in Sweden and includes information such as age, gender, date of visit, primary discharge diagnosis and up to 7 secondary diagnoses in accordance with ICD-10, as assigned by the treating medical doctor. The PDR provides data on all prescribed medications since 2005 and contains identity data for >99.7% of patients. Both registers cover the time period being investigated
†Specifically autism, atypical autism, anxiety, Asperger’s syndrome, bipolar disorder, depression, eating disorder, impulse-control disorder, personality disorder, oppositional defiant disorder, schizophrenia and substance-use disorder
‡Including osmotic release oral system methylphenidate (OROS-MPH), immediate-release methylphenidate, modified-release methylphenidate, atomoxetine, amfetamine, dexamfetamine and modafinil. Although atomoxetine and OROS-MPH were not approved for use in adults during the study period, both were used off-label in adults. Modafinil is prescribed off-label for ADHD. Please refer to your own local country prescribing information
Polyzoi M, Ahnemark E, Medin E, et al. Estimated prevalence and incidence of diagnosed ADHD and health care utilization in adults in Sweden – a longitudinal population-based register study. Neuropsychiatr Dis Treat 2018; 14: 1149-1161.