Prevalence,Patient Characteristics,and Pharmacological Treatment of Children,Adolescents,and Adults Diagnosed With ADHD in Sweden

Abstract

Objective: The objective of this study was to describe the epidemiology of diagnosed ADHD and the pharmacological treatment of patients with ADHD in Sweden. Specifically, this study estimates the prevalence of patients with a newly registered diagnosis of ADHD over a 5-year period, and the prevalence of all patients with a registered ADHD diagnoses over a 6-year period in Sweden. Method: Two population-based registries were used as data sources for this study; the National Patient Register (NPR) and the Prescribed Drug Register (PDR). The international Classification of Diseases 10th Revison (ICD-10) was used to identify patients with ADHD. Results: The annual prevalence of ADHD in the general population of Sweden was found to be 1.1 per 1,000 persons in the year 2006 increasing to 4.8 per 1,000 persons in 2011. The corresponding prevalence for newly diagnosed patients increased from 0.6 per 1,000 persons in 2007 to 1.3 per 1,000 persons in 2011. The majority of diagnosed patients received pharmacological treatment, with methylphenidate being the most common dispensed drug. Comorbidities in the autism spectrum were most common for younger patients, while substance abuse, anxiety, and personality disorder were the most common comorbidities in older patients. Conclusion: From 2006 to 2011, the number of patients diagnosed with ADHD has increased in Sweden over all ages. The majority of patients diagnosed with ADHD in Sweden received a pharmacological treatment regardless of age. An ADHD diagnosis was often accompanied with psychiatric comorbidity.

Keywords

ADHD psychostimulants treatment

Introduction

ADHD is a heterogeneous neurobehavioral disorder in children, adolescents, and adults characterized by symptoms of impulsivity, hyperactivity, and inattention. The symptomatology differs between individuals, with some demonstrating predominantly hyperactive and impulsive behavior and others demonstrating mainly inattentive symptoms (American Psychiatric Association [APA], 2000). ADHD is thought to have a biological basis (Cheon et al., 2003; Pliszka, 2005), but all definitions of ADHD are still based on behavioral descriptions and observations (National Collaborating Centre for Mental Health, 2009). Diagnosing ADHD in Sweden requires a comprehensive review of symptoms to assess whether certain criteria are met, achieved through several strands of investigation, including interviews with parents or caregivers, a physical examination, completion of standardized rating scales and ADHD symptom checklists, gathering information from other professionals such as schoolteachers as well as occasionally including tests for cognitive and executive functioning (National Board of Health and Welfare [NBHW], 2002). The standardized and internationally agreed system for assessing and categorizing the symptoms of ADHD is the Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.; DSM-IV-TR; APA, 2000, published by the APA, recently updated to DSM-5; APA, 2013). The diagnoses in the DSM-IV have corresponding codes in the International Classification of Diseases–10th Revision (ICD-10; published by the World Health Organization [WHO]), which is used to report patients and their diagnoses in the National Patient Register (NPR; APA, 2000; Medical Products Agency, 2009; NBHW, 2002; Region Skåne, 2010; WHO, 2007).

In a systematic review, it was estimated that the worldwide-pooled prevalence of ADHD was 5.3% in the population up to 18 years of age (Polanczyk, de Lima, Horta, Biederman, & Rohde, 2007). However, variability in reported prevalence was seen between the studies. Geographic location was believed to play a limited role, and the variability in prevalence may instead be explained by methodological characteristics of studies (Polanczyk et al., 2007). In Sweden, the NBHW has, based on a review of Swedish and international studies, estimated that around 3% to 5% of school-aged children have ADHD (NBHW, 2002). Also, two population-based cohort studies of ADHD among Swedish children have reported prevalence estimates within that range (Kadesjo & Gillberg, 2001; Landgren, Pettersson, Kjellman, & Gillberg, 1996); similar studies and results have been published for neighboring Nordic countries (Dalsgaard, Nielsen, & Simonsen, 2013; Pottegard, Bjerregaard, Glintborg, Hallas, & Moreno, 2012; Suren et al., 2013; Zoega et al., 2011). Although ADHD is commonly conceived of as a childhood behavioral disorder, it has been reported that approximately 50% to 75% of patients diagnosed in childhood continue to experience symptoms into adulthood (Biederman, Wilens, & Spencer, 2007; Faraone, Biederman, & Mick, 2006). Although less studied, reported estimates for the prevalence of ADHD in adults range from 2.5% to 5.0% (Faraone & Biederman, 2005; Fayyad et al., 2007; Kessler et al., 2006; Nylander, Holmqvist, Gustafson, & Gillberg, 2013; Simon, Czobor, Balint, Meszaros, & Bitter, 2009; Willcutt, 2012). To our knowledge, the prevalence of ADHD across all ages in the Swedish general population has not previously been reported.

ADHD frequently co-exists with other psychiatric conditions such as oppositional defiant-, conduct-, learning-, anxiety-, substance abuse-, and autism spectrum disorders (Antshel, Zhang-James, & Faraone, 2013) and depression (Kadesjo & Gillberg, 2001; Preuss et al., 2006). Data from the United States based on parental reports for 61,779 children aged 6 to 17 years showed that 66.9% of 5,028 children with ADHD had a comorbid psychiatric or neurodevelopmental disorder (Larson, Russ, Kahn, & Halfon, 2011). A recent study in Sweden using the NPR reported that approximately 50% of pediatric patients diagnosed with ADHD suffered from other psychiatric disorders during the period 2007 to 2009 (Bahmanyara, Sundström, Kaijsera, vonKnorring, & Kielera, 2013).

Several pharmacological treatments are available for the treatment of ADHD, and according to Swedish treatment guidelines at the time of this study, pharmacological treatment should be considered in patients when symptoms are insufficiently controlled by non-pharmacological interventions (Medical Products Agency, 2009). At the time of the present study period (2006-2011), methylphenidate (MPH) was recommended as the first-line treatment choice in most children, adolescents, and adults with ADHD in Sweden, and no drugs were indicated for treatment of newly diagnosed adults with ADHD. However, the continued use of osmotic release oral system–methylphenidate (OROS-MPH) is approved into adulthood if effect during childhood has been established and, since 2013, atomoxetine (ATX) has been approved for use in newly diagnosed adults with ADHD (FASS, SPC, 2011a, 2011b; Medical Products Agency, 2009). At the time of this study, amphetamines (amphetamine and dexamphetamine) were recommended as a last treatment option in Sweden and only available on a named-patient basis (Medical Products Agency, 2009). Modafinil, indicated for treatment of narcolepsy (Teva Pharma B.V., SPC, 2013), was not mentioned in the ADHD treatment guidelines but is sometimes prescribed off-label within this population as some evidence supports its efficacy in patients with ADHD (Kumar, 2008). Since December 2013, long-acting prodrug lisdexamfetamine (Elvanse) is available in Sweden. In Sweden, restrictions apply to which prescriber initiates and maintains pharmacological therapy; only specialists in child and adolescent psychiatry, adult psychiatry, and pediatric neurologists are certified and trained to assess, diagnose, and initiate pharmacological treatment in patients with ADHD (Medical Products Agency, 2009).

As the NBHW holds two comprehensive specialist care patient data registries that are mandatory to report to, the NPR and the PDR (Prescribed Drug Register), Sweden is a favorable country for studying the ADHD population with regard to patient characteristics and their pharmacological treatment. Previous studies have used the PDR to describe the use of ADHD medications in children, adolescents, and adults in Sweden (NBHW, 2012; Zetterqvist, Asherson, Halldner, Langstrom, & Larsson, 2013). Zoega and colleagues reported a considerable national variation in prescription rates between the Nordic countries, with Sweden having a prescription rate close to the average between countries (Zoega et al., 2011). Other main findings from previous Swedish ADHD drug-use studies using the PDR include an increase in ADHD drug prescription over time, visible in both genders and all age groups (NBHW, 2012; Stiftelsen nätverk för läkemedelsepidemiologi, 2012) and high rates of treatment discontinuation in adolescents and young adults (Zetterqvist et al., 2013). However, to the best of our knowledge, only two previous peer-reviewed studies have combined the information from the NPR and PDR to investigate ADHD, thus mapping patients with a registered diagnosis of ADHD in Sweden with their pharmacological treatment (Bahmanyara et al., 2013; Larsson et al., 2013). Larsson and colleagues studied the heritability of clinically diagnosed ADHD restricting the study to twins. Bahmanyara and colleagues restricted the population to a cohort below the age of 19 years of age diagnosed with ADHD in 2006 to 2007, which were followed until the year 2009.

Objective of This Study

The objective of this study was to describe the epidemiology of patients with a registered diagnosis of ADHD in all ages in Sweden. Prevalence of a registered diagnosis, prevalence of a newly registered diagnosis, comorbidities, and pharmacological treatment were compared across children, adolescents, and adults to show how prevalence and treatment patterns differ between age groups. The study was approved by the regional ethics board at the Karolinska Institute in Stockholm.

Materials and Method

The NPR was originally set up in the 1960s when the NBHW started to collect information regarding inpatients at public hospitals but now also includes outpatient specialist clinic visits and admissions and visits to private hospitals. The NPR has nationwide coverage for psychiatric outpatient care since 2001. Every record has a discharge date/date of visit, a primary discharge diagnosis, and up to seven secondary diagnoses assigned by the treating medical doctor according to ICD-10. The reporting for somatic care is very robust, whereas the reporting of patients with psychiatric disorders, in general, and ADHD, in particular, was approximately 75% complete in 2011 (NBHW, 2012).

The NPR was used to identify patients who have received a registered diagnosis of ADHD by a clinician, either as a primary or secondary diagnosis. ADHD was defined using the ICD-10 codes relevant for the different subtypes of ADHD defined in the DSM-IV, namely, the ICD-10 codes for hyperkinetic disorders (F90.0-F90.8).¹ Prevalent psychiatric comorbidities among the population with ADHD were collected based on the registered diagnoses of the patient. In 2005, the Swedish government introduced a mandatory registration system of all drugs dispensed at pharmacies, the PDR, to achieve safer prescribing. In the PDR, drug identity is listed according to the Anatomical Therapeutic Chemical (ATC) classification system. In addition to drug identification, the PDR contains information regarding the quantity and dose of the drugs prescribed, together with date of prescription and date for dispensing. The PDR covers the entire population of Sweden, and the identity of the patients is available for >99.7% of the entries (Wettermark et al., 2007). Quality controls are performed on both registries, for example, confirming that compulsory variables like unique personal registration number, hospital, and main diagnosis are reported. The unique identifier, based on each individual’s personal identification number, a number unique to each resident in Sweden, was used as key to link the NPR and the PDR. Pharmacological treatment patterns were assessed by collecting dispensed treatments using the ATC substring “N06BA,” which includes all centrally acting sympathomimetics. Within this group, all drugs indicated for the treatment of ADHD are included (i.e., N06BA04 for MPH and N06BA09 for the non-stimulate ATX), as well as other stimulants such as modafinil (N06BA07), amphetamine (N06BA01), and dexamphetamine (N06BA02), which are used on a named-patient basis for the treatment of ADHD. The substances used for the treatment of ADHD are sold under various formulations and brand names. In this study, MPH is divided into methylphenidate–immediate release (MPH-IR), methylphenidate–modified release (MPH-MR), and OROS-MPH.

Statistical Analysis

A cross-sectional analysis of all patients diagnosed with ADHD during the period 2006 to 2011 was performed. Patients with at least one observation in the NPR with an ADHD-related diagnosis were included, and the annual prevalence of ADHD was defined as the proportion of individuals with an ADHD diagnosis of the total population in Sweden stratified by year. A longitudinal analysis was also performed to estimate the number of patients newly diagnosed with ADHD during the period 2007 to 2011. Newly diagnosed patients were defined by only including patients with no ADHD observations in the NPR or PDR at least 1 year prior to their index ADHD observation in the NPR. The annual prevalence of newly diagnosed patients was defined as the proportion of individuals with a new ADHD diagnosis of the total population in Sweden stratified by year. The population figures used for the estimation of prevalence were taken from Statistics Sweden (Statistiska centralbyrån, 2013) using the current population for the years 2006 to 2011 (see Tables 3 and 4). SAS Version 9.3 (SAS Institute, Inc., Cary, NC, USA) was used in all statistical analyses; the statistical level of significance was set to 5%.

Results

Estimated Prevalence of Diagnosed ADHD in Sweden

There were 71,127 unique patients identified as diagnosed with ADHD in the NPR between January 1, 2006, and December 31, 2011, and out of these, there were 44,057 patients identified having a new diagnosis of ADHD between January 1, 2007, and December 31, 2011. The demographics of the samples are presented in Tables 1 and 2. The proportion of males was 72.7% in 2006 with a decrease to 62.7% (p < .0001) in 2011. The mean age of patients with diagnosed ADHD has also significantly increased within the 6-year period, with a mean age of 19.0 years of age (95% confidence interval [CI] = [18.7, 19.2]) in 2006 to 23.7 years of age (95% CI = [23.2, 23.4]) in 2011. The annual prevalence of diagnosed ADHD in Sweden was 1.1 per 1,000 persons in the year 2006 and increased to 4.8 per 1,000 persons in 2011 (Table 3; p < .0001). The prevalence for women increased from 0.6 in 2006 to 3.6 in 2011 per 1,000 persons, and the prevalence for men increased from 1.6 in 2006 to 6.1 in 2011 per 1,000 persons (both p < .0001).

Table 1.

Characteristics of Patients With an ADHD Diagnosis, Identified for Inclusion in the Cross-Sectional Study Data Set.

Characteristic	2006 (n = 9,929)	2007 (n = 14,028)	2008 (n = 20,157)	2009 (n = 27,114)	2010 (n = 36,109)	2011 (n = 45,818)
Age in years, M (SD), median	19.0 (11.5), 15.0	20.6 (12.1), 16.0	22.0 (12.5), 18.0	22.5 (12.7), 18.0	23.4 (13.5), 19.0	23.3 (13.1), 19.0
Gender, n (%)
Males	7,222 (72.7)	9,858 (70.3)	13,617 (67.6)	17,908 (66.1)	23,055 (63.9)	28,737 (62.7)
Females	2,707 (27.3)	4,170 (29.7)	6,540 (32.4)	9,206 (33.9)	13,054 (36.1)	17,081 (37.3)
Age groups, n (%)
0-5 years	170 (1.7)	176 (1.2)	239 (1.1)	281 (1.0)	330 (0.9)	419 (0.9)
6-11 years	2,396 (24.1)	2,816 (20.1)	3,613 (17.9)	4,609 (17.0)	5,707 (15.8)	7,313 (16.0)
12-17 years	3,713 (37.3)	4,832 (34.5)	6,172 (30.6)	7,839 (28.9)	9,765 (27.0)	12,314 (26.9)
18-21 years	983 (9.9)	1,575 (11.2)	2,488 (12.3)	3,572 (13.2)	5,084 (14.1)	6,420 (14.0)
≥22 years	2,667 (26.8)	4,629 (33.0)	7,645 (37.9)	10,813 (39.9)	15,223 (42.2)	19,352 (42.2)

Table 2.

Characteristics of Newly Diagnosed Patients, Identified for Inclusion in the Longitudinal Study Data Set.

Characteristic	2007 (n = 5,148)	2008 (n = 6,952)	2009 (n = 8,539)	2010 (n = 10,966)	2011 (n = 12,452)
Age in years, M (SD), median	21.2 (12.7), 17.0	22.2 (13.0), 18.0	22.0 (13.1), 18.0	23.5 (15.3), 19.0	22.3 (13.7), 18.0
Gender, n (%)
Males	3,493 (67.9)	4,462 (64.2)	5,402 (63.3)	6,666 (60.8)	7,482 (60.1)
Females	1,655 (32.1)	2,490 (35.8)	3,137 (36.7)	4,300 (39.2)	4,970 (39.9)
Age groups, n (%)
0-5 years	136 (2.6)	183 (2.6)	217 (2.5)	254 (2.3)	295 (2.4)
6-11 years	1,154 (22.4)	1,417 (20.4)	1,762 (20.6)	2,237 (20.4)	2,725 (21.9)
12-17 years	1,386 (26.9)	1,673 (24.1)	2,138 (25.0)	2,494 (22.7)	3,004 (24.1)
18-21 years	542 (10.5)	789 (11.3)	915 (10.7)	1,239 (11.3)	1,345 (10.8)
≥22 years	1,930 (37.5)	2,890 (41.6)	3,507 (41.1)	4,742 (43.2)	5,083 (40.8)

Table 3.

Estimated Annual Prevalence of Patients Diagnosed With ADHD in Sweden, 2006-2011.

	2006 (n = 9,929)	2007 (n = 14,028)	2008 (n = 20,157)	2009 (n = 27,114)	2010 (n = 36,109)	2011 (n = 45,818)
Prevalence, total per 1,000 persons	1.1	1.5	2.2	2.9	3.8	4.8
Prevalence, males per 1,000 persons	1.6	2.2	3.0	3.9	4.9	6.1
Prevalence, females per 1,000 persons	0.6	0.9	1.4	2.0	2.8	3.6

Note. Cross-sectional study data set; annual population figures in Sweden, 2006: Females = 4,589,734, males = 4,523,523; 2007: Females = 4,610,606, males = 4,563,921; 2008: Females = 4,653,177, males = 4,603,710; 2009: Females = 4,691,668, males = 4,649,014; 2010: Females = 4,704,817, males = 4,690,244; 2011: Females = 4,756,021, males = 4,726,834.

The observed trends for all patients diagnosed with ADHD are also evident in patients newly diagnosed with ADHD. In 2007, 5,148 diagnosed with ADHD were present in the register compared with 12,452 in 2011. The proportion of males decreased from 67.9% to 60.1% (p < .0001) and the mean age increased significantly from 21.2 (95% CI = [20.8, 21.5]) in 2007 to 22.3 (95% CI = [22.0, 22.5]) in 2011. The estimated prevalence of newly diagnosed patients increased from 0.6 per 1,000 persons in 2007 to 1.3 per 1,000 persons in 2011, and the prevalence for newly diagnosed women increased from 0.4 to 1.0 per 1,000 persons and for men 0.8 to 1.6 per 1,000 persons (Table 4).

Table 4.

Estimated Annual Prevalence of Newly Diagnosed Patients in Sweden, 2007-2011.

	2007 (n = 5,148)	2008 (n = 6,952)	2009 (n = 8,539)	2010 (n = 10,966)	2011 (n = 12,452)
Prevalence, total per 1,000 persons	0.6	0.8	0.9	1.2	1.3
Prevalence, males per 1,000 persons	0.8	1.0	1.2	1.4	1.6
Prevalence, females per 1,000 persons	0.4	0.5	0.7	0.9	1.0

Note. Longitudinal study data set; annual population figures in Sweden, 2007: Females = 4,610,606, males = 4,563,921; 2008: Females = 4,653,177, males = 4,603,710; 2009: Females = 4,691,668, males = 4,649,014; 2010: Females = 4,704,817, males = 4,690,244; 2011: Females = 4,756,021, males = 4,726,834.

Disturbance of activity and attention was the most prevalent registered diagnoses code with 66.2% of all patients with ADHD having an F90.0 designation in the NPR in 2006. During the study period, the F90.0 code became less prevalent while the F90.0B code, a subset of the F90.0 code developed for ICD-10 system used in Sweden, increased from 24.8% in 2006 to 48.2% in 2011. This is mirrored in the patients newly diagnosed with ADHD where 28.5% of individuals’ first recorded ADHD code was F90.0B in 2007 compared with 42.2% in 2011 accompanied with a decrease in the more general ICD-10 code F90.0 (data not shown).

The Pharmacological Treatment of ADHD in Sweden

It was found that 80.0% of all patients with an ADHD diagnosis in the NPR had at least one entry in the PDR for the defined ADHD drugs (“N06BA”); hence, they were treated pharmacologically at some point over the 6-year study period. For the newly diagnosed patients, the corresponding number was 72.1% over the 5-year period. In the age group 0 to 5 years, a proportion of 61.8% was treated pharmacologically, in the age groups 6 to 11 years, 12 to 17 years, 18 to 21 years, and 22 years and above, the corresponding percentages were 83.1%, 84.7%, 78.1%, and 76.5%. The rank order of the newly diagnosed patients was similar to all patients with ADHD: age group 0 to 5 years had 58.3%, age group 6 to 11 years had 77.6%, age group 12 to 17 years had 79.2%, age group 18 to 21 years had 68.8%, and age group 22 and above had 68.2%.

The proportions of ADHD medications prescribed and dispensed to patients with ADHD are presented in Figure 1. MPH dominates with 83.5% of all prescriptions that where dispensed during the period 2006 to 2011. ATX accounts for 13.1% of all prescriptions followed by amphetamines (amphetamine and dexamphetamine) at 2.9% and modafinil at 0.7%. Extended release MPH (OROS-MPH) is the most commonly dispensed pharmaceutical product representing 52% of all prescribed ADHD drugs, followed by MPH-MR with 29% and ATX with 13% during the time period 2006 to 2011. MPH-IR represented only 2% of the total dispensed ADHD medication during the study period. The proportions of prescribed substances that were dispensed per age group are presented in Figure 2.

Figure 1.

Proportion of prescriptions for ADHD drugs in Sweden, 2006-2011.

Figure 2.

Proportion of prescriptions for ADHD drugs in Sweden, 2006-2011, per age group.

The change in proportions of prescribed and dispensed medications in the 2006 to 2011 period is presented in Figure 3. The proportions of amphetamine, dexamphetamine, and modafinil have decreased from 2006 to 2011, 3.3% to 0.5%, 3.2% to 1.8%, and 1.1% to 0.4%, respectively. The proportion of ATX initially increased from 7.7% in 2006 to a maximum of 15.2% in 2008, and then decreased between the years 2009 and 2011 (2009: 14.2%, 2010: 13.0%, and 2011: 12.4%). The proportions of dispensed prescriptions of MPH in the formulations of IR (from 0.0% in 2006 to 3.9% in 2011) and MR (from 25.6% in 2006 to 31.2% in 2011) have increased over the study period. Interestingly, the dominating MPH, OROS-MPH, has seen a decrease in the proportion of prescriptions, from close to 60% of total prescriptions in 2006 to approximately 50% in 2011 (59.2% in 2006 to 49.2% in 2011, p < .0001).

Figure 3.

Proportion of prescriptions for ADHD drugs in Sweden, 2006-2011, per year.

Comorbidities of Patients With ADHD in Sweden

Patients 22 years and above had the largest frequency of registered psychiatric comorbidities both in newly diagnosed patients (data not shown) and for all patients with an ADHD diagnosis. The most prevalent psychiatric comorbidities among adults (sum of age groups 18-21 years and 22 years and above) were found to be substance abuse (15.1%) and anxiety (12.1%). Among children and adolescents, autism, Asperger syndrome, and oppositional defiant disorder were the most prevalent registered comorbidities (Table 5). Across age groups, depression, anxiety, bipolar disorder, personality disorder, and substance abuse increased with age in co-occurrence with ADHD, whereas oppositional defiant disorder and disorders in the autism spectrum declined.

Table 5.

Psychiatric Comorbidities in Patients With ADHD.

	Age 0-5 (n = 1,326)	Age 6-11 (n = 15,232)	Age 12-17 (n = 24,462)	Age 18-21 (n = 13,437)	Age ≥ 22 (n = 29,746)
Comorbidity, n (%)
Any	201 (15.2)	1,932 (12.7)	3,607 (14.7)	3,402 (25.3)	10,783 (36.3)
Depression	0 (0.0)	15 (0.1)	200 (0.8)	443 (3.3)	2,917 (9.8)
Anxiety	4 (0.3)	182 (1.2)	1,113 (4.5)	1,148 (8.5)	4,089 (13.7)
Bipolar disorder	2 (0.2)	83 (0.5)	394 (1.6)	511 (3.8)	2,775 (9.3)
Personality disorder	0 (0.0)	1 (0.0)	49 (0.2)	573 (4.3)	3,170 (10.7)
Oppositional defiant disorder	14 (1.1)	567 (3.7)	693 (2.8)	40 (0.3)	3 (0.0)
Asperger syndrome	40 (3.0)	837 (5.5)	1,582 (6.5)	1,187 (8.8)	2,476 (8.3)
Autism	144 (10.9)	849 (5.6)	805 (3.3)	293 (2.2)	213 (0.7)
Atypical autism	48 (3.6)	516 (3.4)	747 (3.1)	269 (2.0)	423 (1.4)
Substance abuse	1 (0.1)	2 (0.0)	314 (1.3)	961 (7.2)	5,546 (18.6)

Note. n is the total number of individuals in each age group over the study time. Depression: F33.0-F33.9; anxiety: F41.2-F41.9; bipolar disorder: F31.0-F31.9; personality disorder: F60.0-F60.9; oppositional defiant disorder: F91.3; Asperger syndrome: F84.5; autism: F84.0; atypical autism: F84.9; substance abuse: F10.2-F19.2.

Discussion

Administrative prevalence estimations only captures registered diagnoses (e.g., patients entered into the NPR). The discrepancy between diagnosed cases and unrecognized ADHD in Sweden is an interesting potential topic for another study. Nevertheless, the results of this study are in line with recent findings for the ADHD population in Sweden (Bahmanyara et al., 2013; Zetterqvist et al., 2013) and in neighboring Nordic countries (Dalsgaard et al., 2013; Pottegard et al., 2012; Suren et al., 2013), showing an increasing number of patients diagnosed with ADHD and treated with ADHD medication in recent years. In this study, number of patients with a newly registered diagnosis of ADHD instead of incidence as the newly diagnosed patients could not be assumed to be incident cases of ADHD as they may have had onset of symptoms in the distant past and had delayed seeking care. Also, ADHD is a chronic condition with ambiguous onset, therefore, similar to depression, ADHD is usually defined in terms of prevalence rather than incidence. The annual prevalence of newly diagnosed patients increased from 0.6 in 2007 to 1.3 per 1,000 persons in 2011. The estimated prevalence of all patients with an ADHD diagnosis in 2006 was found to be 1.1 per 1,000 persons and 4.8 per 1,000 persons in 2011 (19.0 in 2006 and 23.7 in 2011). The mean age of patients diagnosed with ADHD increased between 2006 and 2011, with a slight increase in the mean age of new diagnoses (21.2 in 2007 and 22.3 in 2011); supporting previous evidence that, for a substantial proportion of patients, childhood ADHD is carried on into adulthood with a continued impact of the condition on both personal and professional life (Klein et al., 2012; Murphy & Barkley, 1996; Rosler, Casas, Konofal, & Buitelaar, 2010; Wilens, Faraone, & Biederman, 2004). As also reported by Bahmanyara et al. (2013), the proportional increase in number of patients with an ADHD diagnosis was larger for females than for males, which could be due to an increased awareness of ADHD in females (Polanczyk et al., 2007). The study results also showed a shift in the ICD-10 codes used to identify patients with attention and hyperactivity problems with more patients being diagnosed with the more specific five-letter ICD-10 code F90.0B (ADHD) than the more general (F90.0).

Approximately 80% of patients with an ADHD diagnosis in the NPR received pharmacological treatment with an ADHD medication. The corresponding proportion for newly diagnosed patients was 70%. The main drug for ADHD treatment was MPH, across all age groups and genders, which is in line with the Swedish Treatment Guidelines. The most common formulation of MPH was found to be OROS-MPH. Since the introduction of ATX in Sweden in 2006, the use of OROS-MPH has declined. The proportion of prescriptions for ATX accounted for 7.7% of the total in 2006, increasing to 15.2% in 2008 before declining to 12.4% in 2011. The analysis across all age groups showed that treatment with ADHD drugs was most prevalent in the age group 12 to 17 years and least prevalent in the age group 0 to 5 years. Pharmacological treatment is not recommended in children with ADHD below the age of 6 in Sweden (Zetterqvist et al., 2013), which may explain the lower proportion of treated individuals within this age group. OROS-MPH was the most prevalent formulation in age groups over 5 years, MPH-MR was most dominant in the age group up to 5 years, and MPH-IR represents a larger proportion of prescriptions for the age group up to 5 years than the other age groups. A plausible explanation for this difference is that IR and MR preparations are shorter acting than OROS preparations, which is preferable in the preschool children to minimize side effects. Another reason may be the availability of lower strengths. OROS-MPH is available in Sweden in strengths ranging from 18 to 54 mg while different MPH-MR exist in strengths between 5 and 40 mg (TLV, 2013). Overall, there were a slight but significant higher proportion of males than females treated with ADHD drugs. The use of amphetamine and dexamphetamine was low across all age groups and decreased with time in line with findings by Bahmanyara et al. (2013). The use of modafinil in the defined population was low across age groups and time.

The proportion of ADHD patients with comorbidities was high, and the profile of co-existing disorders was different between age groups. The most common overall comorbidity among adults 22 years and above was substance abuse disorder. For age groups up to 5 years and 6 to 11 years, the most common comorbidities were found within the autism spectrum. For the age group 12 to 17 years, the most common comorbidity was Asperger syndrome, and for 18 to 21 years Asperger syndrome and anxiety. Severe levels of hyperactivity and impulsivity have been shown to make children more likely to develop substance abuse in later adolescence and adult life (Barkley, Fischer, Smallish, & Fletcher, 2004; Klein et al., 2012) and substance abuse was the most prevalent comorbidity for the age group 22 years and above (see Table 5).

As with all studies of administrative databases, there are limitations. It is assumed that the patient has the behavior disorder or disease and that they receive a pharmacological treatment based on hospital and outpatient clinic records (including psychiatrist’s records) and prescription dispensing records. This evidence may contain errors due to inaccurate coding, misdiagnosis, or fraud, and the coverage may not be complete. The coverage of psychiatric health care activities in the NPR is approximately 75%; therefore, 25% of all visits are not recorded and therefore not included in the analysis. This means that the prevalence figures presented could be underestimated by up to one third. In addition, data for non-pharmacological treatment were not included in the registries used for the study and are therefore not included. This lack of complete ascertainment of health care encounters places limitation on our definition of ADHD cases. In addition, patients may have been diagnosed with ADHD or received treatment for ADHD prior to 2006 with a gap in treatment or in health care contacts, re-appearing during the study years to be included as newly diagnosed patients. Furthermore, the identification of ADHD diagnoses was based on ICD-10 codes in the NPR, which does not precisely match DSM-IV categorization. Furthermore, the ICD-10 code of F98.8, which is also typically referred to in the DSM-IV categorization for ADHD, was never retrieved.

Conclusion

From 2006 to 2011, the number of patients diagnosed with ADHD has increased in Sweden, an increase seen across all age groups. The majority of patients who received an ADHD diagnosis in Sweden also received a pharmacological treatment regardless of age and gender—the majority received a formulation of MPH. However, approximately 30% of newly diagnosed ADHD patients had no pharmacological treatment. An ADHD diagnosis was often accompanied with other psychiatric disorders. To get the complete picture of ADHD treatment in Sweden, new research should include quantification of the provision of non-pharmacological treatment, that is, behavioral training, parental support, school assistance, either as first-line or as an adjunct to medication.

Summary Points

In Sweden, the prevalence of patients diagnosed with ADHD has increased in all age groups, with larger proportional increases in females and the age group 22 years and above—signaling increased awareness of ADHD in these sub-groups.

In all, 80.0% of all patients diagnosed with ADHD had pharmacological treatment during the 6-year study period. The age group 12 to 17 years had the highest proportion of pharmacological treatment at 84.7%.

A total of 61.8% of patients (819 of a total of 1,326 patients) in the age group up to 5 years were dispensed at least one defined ADHD drug during the study period, a group seldom studied in relation to the pharmacological treatment of ADHD.

MPH is the predominant treatment choice in Sweden with 83.5% of all prescriptions during the period 2006 to 2011, with OROS-MPH being the most dispensed ADHD drug.

The number of patients diagnosed with ADHD with comorbidities was high. The most common comorbidity among children and adolescents was an autism spectrum diagnosis, and for adults, substance abuse disorders.

Across age groups, the comorbidity profile of ADHD changes, while the choice of ADHD medication (substance) remains relatively stable.

Footnotes

Acknowledgements

Under the direction of the authors, Ida Svederud, an employee of HERON Evidence Development AB, provided writing assistance for this publication. Amina Elsner from Shire AG, Switzerland, also reviewed and edited the manuscript for scientific accuracy.

Authors’ Note

Although the sponsor was involved in the design, collection, analysis, interpretation, and fact checking of information, the content of this manuscript, the ultimate interpretation, and the decision to submit it for publication in Journal of Attention Disorders was made by the authors independently. Peter Carlqvist is now at Novartis, and Leo J. Russo is now at Pfizer, Inc.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Peter Carlqvist was at the time of the study employed by HERON Evidence Development AB. Emma Medin is employed by HERON Evidence Development AB, which has been financially supported by Shire. Ewa Ahnemark is employed by Shire and hold stock/stock options in Shire. Shire develops and manufactures treatments for psychiatric disorders including ADHD. MaiBritt Giacobini is on an ADHD Advisory Board for Eli-Lilly and has participated in a Nordic ADHD Expert Group for Shire. Leo J. Russo was at the time of the study employed by Shire.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was funded by the Sponsor, Shire Sweden AB. Shire Sweden AB provided funding to HERON Evidence Development AB for support in writing and editing this manuscript. Caudex Medical, funded by Shire International GmbH, provided administrative assistance.

Notes

Author Biographies

MaiBritt Giacobini, MD, PhD, is a specialist in child and adolescent psychiatry and clinical genetics, and co-founder of PRIMA Child and Adult Psychiatry and currently head of PRIMA Järva, a child and adolescent outpatient clinic in Stockholm.

Emma Medin, MD, MSc in economics, and doctoral student in health economics at the Karolinska Institutet, is a general manager at HERON Evidence Development AB in Stockholm.

Ewa Ahnemark, MD, is a specialist in psychiatry, working at Shire as an associate medical director, Nordic Region, Neuroscience BU.

Leo J. Russo, PhD, is a director of epidemiology, Shire Development, Inc.

Peter Carlqvist, MSc, PhD, is the technical lead at HERON Evidence Development AB.

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