Bipolar disorder in children and adolescents in Germany: national trends in the rates of inpatients, 2000–2007

Authors

  • Martin Holtmann,

    1. LWL-University Hospital for Child and Adolescent Psychiatry, Psychotherapy and Psychosomatics, Ruhr University Bochum, Hamm
    2. Department of Child and Adolescent Psychiatry and Psychotherapy, Central Institute of Mental Health, Mannheim
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  • Eftichia Duketis,

    1. Department of Child and Adolescent Psychiatry and Psychotherapy, Goethe-University, Frankfurt/Main
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  • Luise Poustka,

    1. Department of Child and Adolescent Psychiatry and Psychotherapy, Central Institute of Mental Health, Mannheim
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  • Florian Daniel Zepf,

    1. Department of Child and Adolescent Psychiatry and Psychotherapy, Goethe-University, Frankfurt/Main
    2. Department of Child and Adolescent Psychiatry and Psychotherapy, RWTH Aachen University, Aachen, Germany
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  • Fritz Poustka,

    1. Department of Child and Adolescent Psychiatry and Psychotherapy, Goethe-University, Frankfurt/Main
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  • Sven Bölte

    1. Department of Child and Adolescent Psychiatry and Psychotherapy, Central Institute of Mental Health, Mannheim
    2. Department of Child and Adolescent Psychiatry and Psychotherapy, Goethe-University, Frankfurt/Main
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  • MH is a member of advisory boards for Eli Lilly & Co., Novartis, and Bristol-Myers Squibb; and received speaker honoraria from Eli Lilly & Co., AstraZeneca, and Shire. FDZ is the recipient of an unrestricted educational award presented by the American Psychiatric Association and AstraZeneca, which is not related to this study. FP is a member of advisory boards for Eli Lilly & Co., Janssen Cilag, AstraZeneca, and Novartis. ED, LP, and SB have no financial relationships to disclose.

Corresponding author:
Martin Holtmann, M.D.
LWL-University Hospital for Child and
Adolescent Psychiatry, Psychotherapy and Psychosomatics
Heithofer Allee 64
D 59071 Hamm, Germany
Fax: 0049-2381-893-119
E-mail: martin.holtmann@wkp-lwl.org

Abstract

Holtmann M, Duketis E, Poustka L, Zepf FD, Poustka F, Bölte S. Bipolar disorder in children and adolescents in Germany: national trends in the rates of inpatients, 2000–2007.
Bipolar Disord 2010: 12: 155–163. © 2010 The Authors.
Journal compilation © 2010 John Wiley & Sons A/S.

Objectives:  Increasing admission and prevalence rates of bipolar disorder (BD) are a matter of controversy in international child and adolescent psychiatry. We seek to contribute to this discussion by presenting data obtained in a population of German children and adolescents.

Methods:  Nationwide, whole population changes in inpatient admissions of BD and other psychiatric disorders between 2000 and 2007 were analyzed in individuals aged up to 19 years using registry data from the German Federal Health Monitoring System.

Results:  Inpatient admissions for BD in individuals aged up to 19 years increased from 1.13 to 1.91 per 100,000 or 68.5% between 2000 and 2007 (odds ratio: 1.69; 95% confidence interval: 1.41–2.02), with a nonsignificant decline in children less than 15 years and the largest relative increase in adolescents aged 15–19 years. Inpatient rates for depressive disorders increased by 219.6% and for hyperkinetic disorder by 111.3%. Conduct disorders increased by 18.1%, considerably less than the 38.1% general rise for all mental disorders in children and adolescents. The only significant decline in a diagnostic category occurred for psychotic disorders (−11.8%). BD inpatient admission represented only 0.22% of all mental disorder admissions in 2000 and 0.27% in 2007.

Conclusions:  An elevation of inpatient admissions of BD in Germany in adolescents was detected, exceeding the general trend for increased mental disorder admissions. The results may indicate a higher clinical awareness and appreciation of mood symptoms at earlier ages and, in part, a reconceptualization of previously diagnosed psychotic disorders in youth. However, a diagnosis of BD in youngsters is still extremely rare in Germany. Diagnoses were based on the judgment of the treating physician. A correction for multiple admissions in the data set is not possible.

A growing body of research demonstrates increasing rates of bipolar disorder (BD) in clinical samples of children and adolescents, particularly in the U.S. (1–3). While there is little dispute about the validity of the diagnosis of BD in postpubertal youths per se, the rising rate of prepubertal children being diagnosed with BD, the extent of this increase, and the underlying reasons are a matter of ongoing controversy in international child psychiatry (4, 5).

In their study on U.S. trends in the outpatient diagnosis of BD, Moreno et al. (3) reported a nearly 40-fold increase of office-based visits with a diagnosis of BD from 1994 to 2003 in children and adolescents aged up to 19 years (from 2.5 to 100.3 visits per 10,000 population). Blader and Carlson (1) observed a fivefold increase of population-adjusted rates of hospital discharges of children with a primary diagnosis of BD from 1996 to 2004 (from 1.3 per 10,000 U.S. children to 7.3 per 10,000) and a fourfold increase among adolescents (from 5.1 to 20.4 per 10,000), while adults showed a more modest, though still marked, rise of 56% (from 10.4 to 16.2 per 10,000). Harpaz-Rotem and Rosenheck (2) reported an increase in children under the age of 18 with a diagnosis of BD from 5.1 per 10,000 in 1995 to 9.6 per 10,000 in 2000, accompanied by a considerable reduction in the likelihood of diagnoses of oppositional defiant disorder (ODD) and conduct disorder (CD).

There is no compelling reason to presume that the frequency of BD in children and adolescents is actually much higher in the U.S. than in Europe. Therefore, there is considerable European skepticism about the high prevalence rate of BD in children in the U.S. The diagnosis of BD in youngsters is fairly rare outside of the U.S. In a review on international epidemiological data of BD in youngsters, Soutullo et al. (4) reported prevalence rates in clinical inpatient samples of children and adolescents of 1.2% in Denmark, 1.7% in Finland, and 2.5–4.2% in India. In a recent study, Lazaro et al. (6) report diagnoses of BD in 2.2% of inpatient children and adolescents in Spain. In contrast, prevalence rates of BD in U.S. clinical samples range from 5.9% to 30% (e.g., 1, 7, 8). However, subject ascertainment, clinical settings, and ages differed across studies. In German child psychiatric inpatient samples, BD is rarely diagnosed [∼0.2% (9)]. To date, there is no evidence available for nationwide hospitalization rates in Germany, by population the largest country in Europe.

We seek to contribute to the discussion on the increasing rates of BD in youngsters using whole-population report data from the German Federal Health Monitoring System in order to analyze national trends of inpatient visits of BD in Germany for the years 2000 to 2007. These data are complemented by an analysis and discussion of other possible discharge diagnoses that could have changed as a result of a presumed increase in BD diagnosis.

Using this approach, we wanted to explore whether the data might help to answer the following questions: (i) Did rates of BD in children and adolescents increase during the study period? (ii) Is a presumed increase in BD accompanied by a decrease in other psychiatric discharge diagnoses, suggestive of a diagnostic shift (e.g., from hyperkinetic, oppositional, depressive, or psychotic disorders to BD)? (iii) Does the rate of BD diagnoses in young adults from 20 to 30 years stagnate or decrease, leading to the assumption of a diagnostic ‘spill-over’, bringing forward bipolar diagnoses from adults to younger age groups?

Materials and methods

Source of data

Analyses were based on annual reports provided by the German Federal Health Monitoring System (10). Germany’s hospitals are obliged to report ICD-10 (11) inpatient diagnoses upon discharge to the statistical offices at the state level. Single state reports are then transferred to the Federal Statistical Office and pooled. Nationwide inpatient statistics are made publicly available (http://www.gbe-bund.de). Diagnostic information is grouped for different age groups covering five-year intervals (less than 5 years, 5–9 years, 10–15 years, etc.). In addition, the data set provides yearly figures on the average length of stay in psychiatric care. The inpatient reporting rate of the hospitals to the statistical offices is about 99.5%, with a proportion of unknown diagnoses of less than 0.1%.

Diagnostic groups and statistics

In this study, we examined admission rates in Germany between 2000 and 2007 based on 100,000 of the same age band for the corresponding year for the following disorders and age groups: BD (ICD-10, F31) for children less than 15 years, adolescents from 15 to 19 years, young adults from 20 to 30 years, and adults over 30 years. Admissions per 100,000 individuals up to 19 years are reported for other ICD-10 discharge diagnoses that have been shown to be comorbid with BD or have to be taken into account as differential diagnoses (4, 9): substance-related disorders (F10-F19); psychotic disorders (F20-F29); depressive disorders (F32); neurotic, stress-related, and somatoform disorders (F40-F48); specific personality disorders (F60); hyperkinetic disorders (F90); CD (F91); CD and emotional disorder combined (F92); all mental disorders (F00-F99). Rates per 100,000 were based on population estimates published yearly from the Federal Statistical Office (12). In the year 2000, the German population of children and adolescents up to 19 years comprised 17,390,000 individuals, with a decline to 16,204,000 in 2007.

We computed chi-square analyses comparing the figures from the year 2000 to those of 2007 in order to assess the statistical significance of observed changes. To provide a measure for the magnitude of changes in diagnostic rates from 2000 to 2007, we calculated odds ratios (OR): (admissions for a specific diagnosis in 2007/admissions for all other psychiatric diagnoses in 2007)/(admissions for a specific disorder in 2000/admissions for all other psychiatric diagnoses in 2000). Around OR, we calculated 95% confidence intervals (CI) based on constant chi-square boundaries (13).

To provide a measure for the relative weights of different diagnoses, rates of specific psychiatric disorders in individuals aged up to 19 years were also analyzed as a proportion (in %) of the total of psychiatrically related discharges (F00-F99) in the critical time period. In addition, we examined changes in the number of total inpatient days in psychiatric care and average length of stay.

Results

From 2000 to 2007, there was a 38.1% increase in psychiatric hospital admissions in children and adolescents aged up to 19 years (from 511 to 705 per 100,000) and a 9.0% decline in the mean length of stay (from 24.8 to 22.2 days), resulting in a 13.1% increase in the number of bed-days, from more than 2.20 million to about 2.49 million.

Population figures and the absolute number of inpatient admissions for bipolar disorder in individuals aged 19 years and under are shown in Table 1.

Table 1.   Population figures and inpatient admissions (absolute numbers) for ICD-10-defined bipolar disorder (BD) for individuals 19 years of age and younger in Germany from 2000 to 2007
 20002001200220032004200520062007
Population (million): 0–19 years17.39017.25917.08916.90416.71316.48616.20415.925
Inpatient admissions for BD
 < 15 years1920302317223210
 15–19 years178172157169250273272294
 0–19 years197192187192267295304304

In children less than 15 years, the rate of admissions for BD showed a nonsignificant decline from 0.14 to 0.09 per 100,000 (decrease of 40.4%). Hospitalization rates for BD increased in older age groups, with the largest relative increase in adolescents aged 15 to 19 years (64.1% increase, 3.85 to 6.33 per 100,000). The rates in young adults from 20 to 30 years rose by 55.6% (8.95 to 13.93 per 100,000), and in adults 30 years and older by 45.7% (22.31 to 32.51 per 100,000). Table 2 shows inpatient rates per 100,000 for specific psychiatric diagnoses, corresponding chi-square analyses, levels of significance, OR, and 95% CI.

Table 2.   National inpatient admission rates per 100,000 [odds ratios (OR) and 95% confidence intervals (CI)] for selected ICD-10-defined disorders and age groups in Germany between 2000 to 2007
 Age (yrs)20002001200220032004200520062007χ2p-valueOR95% CI
Bipolar disorder (F31)< 150.140.150.240.180.140.180.270.091.790.1800.5960.282–1.260
15–193.853.703.353.555.225.645.716.3327.76< 0.0011.6411.363–1.976
0–191.131.111.091.141.601.791.871.9133.30< 0.0011.6851.409–2.015
20–308.9510.0710.0211.2212.4012.5914.1213.93104.67< 0.0011.5561.428–1.694
> 3022.3122.7923.7025.2927.4130.1231.6732.511058.29< 0.0011.4571.424–1.491
Substance-related disorders (F10–19)0–19133.44142.30144.45146.79162.36179.51175.61200.992292.30< 0.0011.5071.482–1.533
Psychotic disorders (F20–29)0–1926.0227.7727.5728.3126.5726.8224.4422.9631.64< 0.0010.8820.845–0.922
Depressive disorders (F32)0–1912.5517.1120.0023.4325.2627.1133.6740.132455.13< 0.0013.1963.044–3.355
Neurotic, stress-related, somatoform disorders (F40–48)0–1998.19112.13121.26121.45129.65131.35132.40139.001055.84< 0.0011.3901.363–1.419
Personality disorders (F60)0–1920.7526.4624.9125.1226.2725.3826.3826.63121.91< 0.0011.2831.228–1.342
Hyperkinetic disorders (F90)0–1920.9724.8528.3830.4633.5435.0838.1444.311409.29< 0.0012.1132.030–2.199
Conduct disorder (F91)0–1923.2024.2424.2824.7225.6224.9925.9327.4158.19< 0.0011.1811.132–1.233
Conduct and emotional disorder combined (F92)0–1936.7540.7740.9443.0448.3249.7254.0656.13678.86< 0.0011.5281.479–1.578
All mental disorders (F00–99)0–195115575805846196386537055190.46< 0.0011.3811.369–1.393

While the increase in hospitalizations for all mental disorders in children and adolescents was almost linear, the increase in BD was largely attributable to a rise in adolescents from 2003 to 2004 (from 169 to 250 admissions). Rates of BD in children showed larger fluctuations, including a sharp decrease from 2006 to 2007 (from 32 to 10 admissions).

During the same interval, increases in admissions per 100,000 individuals up to 19 years were observed for the following ICD-10 discharge diagnoses (in descending order): depressive disorders (F32; 219.6%); hyperkinetic disorder (F90; 111.3%); CD and emotional disorder combined (F92; 52.8%); substance-related disorders (F10-F19; 50.7%); neurotic, stress-related, and somatoform disorders (F40-F48; 39.0%); specific personality disorders (F60; 28.3%); CD (F91; 18.1%). When examining decreases in diagnostic proportions, the only significant reduction was an 11.8% decrease of psychotic disorders (F20-F29) in individuals less than 19 years.

The proportion of BD inpatient admissions in relation to all mental disorder admissions in subjects up to 19 years increased from 0.22% in 2000 to 0.27% in 2007. The highest proportions were observed for substance-related disorders (26.9% of all psychiatrically related diagnoses), and neurotic, stress-related disorders (19.7%). While there were decreasing proportions of psychotic disorders (5.1% to 3.7%) and CD (4.5% to 3.9%), diagnoses of depression increased (2.5% to 5.7%). The proportion of other psychiatric diagnoses decreased from 27.02% to 20.63%.

In adults, BD accounted for 2.01% of all psychiatrically related admissions in 2007; the most frequent psychiatric diagnoses were substance-related disorders (38.1%), psychosis (13.6%), neurotic, stress-related disorders (12.5%), and depressive disorders (10.1%). Rates of specific psychiatric disorders as a proportion of the total of psychiatrically related discharges are summarized in Table 3.

Table 3.   Specific psychiatric disorders (ICD-10) as a proportion (%) of the total of psychiatrically-related discharges of children and adolescents (less than 19 years of age) between 2000 to 2007, and adults in the year 2007 in Germany
 Children and adolescentsAdults
200020012002200320042005200620072007
Bipolar disorder (F31)0.220.200.190.200.260.280.290.272.01
Substance-related disorders (F10–19)26.1125.5524.9125.1426.2328.1426.8928.5138.13
Psychotic disorders (F20–29)5.094.994.754.854.294.203.743.2613.60
Depressive disorders (F32)2.463.073.454.014.084.255.165.6910.07
Neurotic, stress-related, somatoform disorders (F40–48)19.2120.1320.9120.8020.9520.5920.2819.7212.53
Personality disorders (F60)4.064.754.304.304.243.984.043.782.87
Hyperkinetic disorders (F90)4.104.464.895.225.425.505.846.290.05
Conduct disorder (F91)4.544.354.194.234.143.923.973.890.02
Conduct and emotional disorder, combined (F92) 7.19 7.32 7.06 7.37 7.81 7.80 8.28 7.96 0.02
Other psychiatric disorders27.0225.1825.3523.8822.5821.3421.5120.6320.7
All mental disorders (F00–99)100100100100100100100100100

Discussion

To our knowledge, this is the first report on diagnostic trends of BD in childhood and youth outside of the U.S. While there was an increase of almost 69% in rates of admission diagnosis for BD, which exceeded the general trend of a rise in admissions for other mental disorder admissions in children and adolescents (38.1%), the overall rate of diagnosis is very low and occurs in adolescents rather than children. This contrasts with U.S. findings where rate increases occur in both children and adolescents.

Interestingly, our figures are close to the 65.4% increase in diagnoses of BD in outpatients under the age of 18 years from 1995 to 2000 reported by Harpaz-Rotem and Rosenheck (2) but far more moderate than the increase in more recent U.S. studies (1, 3), and the estimated underlying prevalence is much lower. In Germany, a diagnosis of BD in childhood is still extremely rare. While Blader and Carlson (1) reported a rate of 73 children and 204 adolescents per 100,000 discharged with a diagnosis of BD in 2004, the rates in Germany (with slightly different age groups) are 0.14 and 5.22 per 100,000. Proportionately, markedly fewer discharges for BD occur in Germany than in the U.S.: in 2004, 34.1% of psychiatric inpatient discharges in the U.S. under age 13, (25.9% of discharges in adolescents and 14.9% in adults) were for BD (1), while in Germany, diagnoses of BD constituted less than 1% of all psychiatrically related discharges in children and adolescents and ∼2% in adults.

Putative reasons for the increase of BD in adolescents in Germany

Our data set enabled us to describe diagnostic trends over time, but it is not within the scope of this retrospective register study to examine the causes of the observed changes. However, three considerations shall be made regarding possible mechanisms behind the increase in admissions for BD.

(i) The observed increase in population-adjusted admissions for BD and a variety of other mental disorders in recent years may not represent a ‘real’ rise in prevalence but may rather reflect rising readmissions due to reduced length of stay (LOS) in psychiatric care. The evidence on the consequences of shorter average LOS on readmission rates in children and adolescents is inconclusive (14). Figueroa et al. (15) demonstrated that slight decreases in LOS may be related to significant increases in the risk of readmission. Even the small decline of the mean LOS throughout our eight-year study period by 9.0% (from 24.8 days to 22.2 days) may have produced a similar artefactual rise in psychiatric admissions. Still, this does not explain the different magnitudes of change for particular disorders (e.g., the rise in depressive and bipolar disorders, and concomitant decrease in psychotic disorders). Unfortunately, no LOS data are available for particular psychiatric diagnoses in the present database. Therefore, more specific explanations for the reported increase in BD may be more valuable.

(ii) Increased rates of BD in children and adolescents may be a consequence of environmental changes in recent years. For instance, some authors argue that greater use of stimulants and antidepressants might be leading to an earlier onset of BD, as they could induce hypomanic or manic episodes in children with a genetic predisposition for BD (16, 17). According to pharmacoepidemiological studies, stimulant prescriptions in Germany have increased considerably over the past decade, from 3 million defined daily doses (DDD) in 1996 to 13 million DDD in 2000, and 39 million DDD in 2006 (18). The prevalence of stimulant prescriptions in the age group 6 to 18 years in the year 2000 was 0.72% and increased to 1.29% in 2006 (19). On the other hand, rates of stimulant prescriptions increased 24-fold (from 0.1/1000 to 2.4/1000) in the 10- to 14-year-olds and more than doubled in the group of 15- to 19-year-olds, while the increase in the rate of BD was limited to older adolescents. That militates against stimulant medication as an explanation for the increase. In addition, an increasing number of studies found that stimulant treatment in children with ADHD plus manic symptoms did not predispose to the development of BD, calling into question the concept of stimulant-induced mania (20–22).

For the use of antidepressants in German children, only a few prevalence figures over time have been published. Utilization trends suggest an expanded use of antidepressants in children, particularly since the late 1990s. For selective serotonin reuptake inhibitors (SSRIs), a doubling of prescriptions in adolescents was observed over the four-year period from 2000 to 2003, but the total proportion of German youths treated with antidepressants has not changed considerably, and the absolute prevalences were low (0.37% for all antidepressants, and only 0.08% for SSRIs in 2003) (23, 24).

(iii) Increased clinician awareness of BD in children and adolescents has likely played a decisive role in the rise of BD diagnoses. It is possible that BD in youngsters, previously under- or misdiagnosed, is now being appropriately recognized. Higher rates of admissions among youth associated with BD may reflect greater appreciation of the importance of affective symptoms in younger patients (3). Publications addressing the theme of underdiagnosed childhood BD in Germany (e.g., 25) may have contributed to this effect.

Against this background, one may raise the question of whether the higher prevalence rates of BD in children and adolescents may simply reflect diagnoses brought forward from adults to younger age groups due to a better understanding of the phenomenological particularities of BD in youth. If the reason for the rise of admissions for BD in youth had been largely the consequence of an earlier identification by clinicians, the prevalence in older age groups should have shown a corresponding decline, assuming that the lifetime prevalence of BD is stable. Our data do not support this hypothesis of an earlier clinical recognition. During the study period, the rate of BD diagnoses in young adults aged 20 to 30 years did not stagnate or decrease but increased by ∼56%. This may be seen as an argument against the assumption of a diagnostic ‘spill-over’. On the other hand, increasing rates in older age strata could reflect a higher incidence of BD among youth. However, due to its lack of patient identifiers, the present data set does not permit individuals to be followed longitudinally. This would have been a prerequisite to adequately address the issue of earlier identification and possible prior misdiagnosis. Alternatively, the rise of BD diagnoses in young adults may also be a consequence of the trend to broaden the concept of BD beyond classical mania to a ‘soft bipolar spectrum’, in Europe as well as in the U.S. (26, 27).

Discrepancies in the BD prevalence between Germany and the U.S.

How do we explain the markedly lower prevalence figures of BD in Germany compared to those reported from different U.S. studies?

(i) Results of a recent survey among German child psychiatrists seem to suggest that there is still some hesitancy to use diagnostic categories such as BD for young patients (9, 25). The proportion of BD inpatient admissions in our study in individuals less than 19 years in relation to all mental disorder admissions in 2007 (0.27%) is in line with the one-year prevalence previously reported from our clinical sample [0.2% (9)] and close to that in the only published German outpatient study [∼0.5% (25)]. These rates are very far below those reported from U.S. clinical samples [∼6–7% of outpatient visits with a mental disorder diagnosis, and ∼15–35% of child and adolescent psychiatric inpatient admissions (1, 3, 7)]. Lower prevalence rates of BD in adolescents than in the U.S. have been reported from other European countries, including the United Kingdom, the Netherlands, Ireland, and Denmark (4), raising the question of how this extreme transatlantic discrepancy might be explained. Given the comparable international rates of BD in adults (with most epidemiologic studies giving rates of bipolar I disorder at 1–2%), there is no convincing explanation to allow us to believe that the frequency of BD in children and adolescents is actually much higher in the U.S. than in Europe.

(ii) A reason for the possible inequality of the frequency of pediatric BD in Europe and the U.S. may lie in ICD-10/DSM-IV-TR differences in diagnostic criteria and associated general assessment methodologies, with DSM criteria being less restrictive. While diagnosis in the U.S. seems to be more cross-sectional and symptom-driven, European clinicians prefer to classify disorders based on pattern recognition (28). Regarding prepubertal mania, Dubicka et al. (28) illustrated how these different conceptualizations subsequently result in differing classifications, despite similar symptoms and comparable phenotypes (29). Using identical case vignettes in which mania might be part of the differential diagnosis, mania was identified more frequently by clinicians in the U.S. than in the U.K. Relatedly, like clinicians in the U.K., German clinicians may be diagnosing only the narrow bipolar phenotype; the broader phenotype, labeled by some as ‘severe mood dysregulation’ (30), is often diagnosed as ‘hyperkinetic conduct disorder’ within the ICD system. The latter finding suggests that the primary intent of operationalized criteria [that different clinicians and researchers are able to identify the same subjects, knowing who each other’s patients are (31)] does not hold for the current practice in the context of BD. Clinicians seem to apply the same diagnostic criteria in inconsistent ways, underlining the need for cross-national diagnostic decision making, reducing the bias of diagnostic preconceptions (28). Beyond the difference in how children are classified diagnostically, one needs to address the question of how different diagnostic categories affect treatment practice.

(iii) As noted earlier, some have questioned whether the higher frequency of stimulant and antidepressant use in the U.S. compared to European countries (24) indeed leads to higher prevalence rates. In addition, recent evidence suggests that misuse of stimulants in adolescents with and without ADHD is more prevalent in the U.S. (32) than in Germany (33), but direct comparison is hampered by variable methodology, terminology, and outcome measures.

(iv) Given the high rates of depression in Germany, one has to wonder if what is being called ‘depression’ in Germany is being called ‘mixed bipolar’ in the U.S.

(v) Other reasons for the transatlantic differences in BD prevalence include aggressive marketing strategies and reimbursement policies (1, 14) in the U.S. compared to Germany. Rising U.S. direct-to-consumer advertising (34) by pharmaceutical companies with product indications for mania is unlikely to account for a great deal of the increased diagnoses of BD in children, since during the years discussed in this study, there were no Food and Drug Administration-approved treatments for mania in children, and therefore advertising was not allowed. More likely, the increased readiness to diagnose BD in aggressive and affectively labile children is linked to the popularity of books on BD written for laypersons and to the increasing awareness of clinicians due to medical education activities emphasizing the diagnosis of BD.

(vi) Finally, a ‘diagnostic upcoding’ to putatively more severe conditions for reimbursement or administrative reasons under the scrutiny of managed care systems has been suggested as a contributing factor for the U.S. trend of increasing bipolar diagnosis in children and adolescents (1). In contrast, admissions to inpatient treatment in Germany are largely directed by the referring physicians and admitting clinicians, with the insurance companies having little room to intervene. In addition, German data protection laws restrict purchasers’ access to medical patient information that would enable them to manage the delivery of health care.

Limitations

The current analysis has several important limitations. First, we report cross-sectional data and administrative referral rates, which do not allow any reliable estimates of population prevalence rates of BD in Germany.

Second, our analysis is restricted to inpatient admissions, and does not include office-based visits, visits to hospital outpatient clinics, or mental health care provided by nonphysicians. This may have led to lower overall administrative prevalence rates. However, our data are comparable in this regard to those reported by Blader and Carlson (1), who also studied inpatient rates for the U.S.

Third, diagnoses in the German Federal Health Monitoring System are based on the judgment of the treating physician rather than on an independent standardized assessment. Due to different individual coding practices, reliability might be low and validity unknown; e.g., some clinicians may have implicitly applied DSM-IV criteria, despite ICD-10 being the official classification system in Germany. In their survey in child and adolescent psychiatrists in Southern Germany, Meyer et al. (25) were able to identify factors modifying the likelihood of diagnosing BD: being a younger psychiatrist and favoring a pharmacological and cognitive-behavioral approach were associated with the likelihood of having diagnosed pediatric or adolescent BD.

Fourth, the data set does not provide patient identifiers; therefore, it is impossible to distinguish index admissions from readmissions and to correct for multiple admissions in the study period. Fifth, the database does not allow analyses to be performed separately for boys and girls, meaning that gender effects cannot be studied. Sixth, no comorbid psychiatric conditions are made available by the data set. Finally, it is important to bear in mind that our findings span a relatively brief time interval of eight years. For the years prior to 2000, no detailed diagnostic statistics for Germany are available. Therefore, we were unable to study a longer period of time. Further studies are needed in order to monitor future developments, changes in service use, and explanatory mechanisms for diagnostic changes.

A strength of this study is the use of a publicly available, nationwide database that others can use to validate our results.

Conclusions

In sum, our data show an increase in the case load for BD in German adolescents in recent years, exceeding the general trend for a rise in admissions for mental disorder admissions in children and adolescents. Our results may indicate an increased clinical awareness and promoted recognition of BD at earlier ages. However, this rise is far more moderate than that reported from U.S. studies, and a diagnosis of BD under the age of 15 years is still extremely rare. While several studies suggest that about one-third of BD cases begin before the age of 19 years (35, 36), in most cases the onset of first symptoms is not accompanied by hospitalization, and it often takes a number of years before the disorder evolves in a way that is recognizable.

The huge discrepancy between rates of BD in youngsters in the U.S. and in Germany emphasizes the need for comparative epidemiological studies that combine formal diagnostic and phenotypic approaches. Naturalistic cross-national prevalence studies are warranted to determine the types and characteristics of treatments that are delivered to youth with specific phenotypes, irrespective of diagnoses. The suggestion of criteria for a range of narrow to broad phenotypes of BD seems to be a useful approach to characterize homogeneous subgroups of BD in a more refined and comprehensive way. These could be differentiated according to clinical characteristics, such as the presence and duration of clearly demarcated affective episodes and hallmark symptoms of elevated mood or grandiosity (30). Such definitions might be used to ascertain the prevalence, diagnostic stability, clinical course, and treatment approaches across phenotypes of children with suspected BD.

Acknowledgement

The authors wish to thank an anonymous reviewer for his/her creative persistence and thoughtful comments and suggestions.

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