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The Attention-Deficit Hyperactivity Disorder
Paradox: 2. Phenotypic Variability in Prevalence and Cost of
Comorbidity
Larry Burd, PhD; Marilyn G. Klug, Larry Burd, PhD; Marilyn G. Klug, PhD; Matthew J. Coumbe, PhD; PhD; Matthew J. Coumbe, PhD;
Jacob Kerbeshian, MDJacob Kerbeshian, MD
Abstract The objective of this study was to use population-based data to The objective of this study was to use population-based data to
estimate the cost and phenotypic variation of conditions comorbid estimate the cost and phenotypic variation of conditions comorbid with attention-deficit hyperactivity disorder (ADHD). The case with attention-deficit hyperactivity disorder (ADHD). The case population was 7745 children. We then examined the 10 most population was 7745 children. We then examined the 10 most frequent comorbidities for a defined condition from the ICD-9. frequent comorbidities for a defined condition from the ICD-9. The observed prevalence of general health conditions was 12 to The observed prevalence of general health conditions was 12 to 70% less than expected. The presence of a comorbid condition 70% less than expected. The presence of a comorbid condition resulted in increases in costs of care of $381 to $731 per case per resulted in increases in costs of care of $381 to $731 per case per year. The observed prevalence of comorbid mental health year. The observed prevalence of comorbid mental health conditions was 97 to 5286% higher than expected. We identified conditions was 97 to 5286% higher than expected. We identified an ADHD paradox: decreased rates of comorbid general health an ADHD paradox: decreased rates of comorbid general health conditions and increased rates of comorbid mental disorders. conditions and increased rates of comorbid mental disorders. Further research on comorbidity in ADHD is required. (Further research on comorbidity in ADHD is required. (J Child J Child NeurolNeurol 2003;18:653-660). 2003;18:653-660).
Study Population
The original data set consisted of 1,509,980 visits The original data set consisted of 1,509,980 visits made by children ages 0 to 21 years in North made by children ages 0 to 21 years in North Dakota in 1996 and 1997. This included both Dakota in 1996 and 1997. This included both inpatient and outpatient visits. For the 2 years inpatient and outpatient visits. For the 2 years combined, a total of 1,473,611 visits were combined, a total of 1,473,611 visits were included in this analysis. This represented included in this analysis. This represented (averaged over 1996 and 1997) visits made by (averaged over 1996 and 1997) visits made by 197,983 uniquely identified children (88,702 in 197,983 uniquely identified children (88,702 in 1996 and 109,281 in 1997).1996 and 109,281 in 1997).
Inclusion Criteria: Cases Patients were included in the study as cases with Patients were included in the study as cases with
ADHD if at any time during either year they had an ADHD if at any time during either year they had an International Classification of Diseases,International Classification of Diseases, 9 9thth edition edition (ICD-9), code of 314.00 or (attention-deficit disorder (ICD-9), code of 314.00 or (attention-deficit disorder not otherwise specified), 314.00 or (inattentive type), not otherwise specified), 314.00 or (inattentive type), 314.01 (with hyperactivity/impulsiveness), or 314.8 314.01 (with hyperactivity/impulsiveness), or 314.8 (with other specific manifestations). The code 314.9 (with other specific manifestations). The code 314.9 (attention-deficit hyperactivity disorder not (attention-deficit hyperactivity disorder not otherwise specified) was also included to capture otherwise specified) was also included to capture cases from the cases from the Diagnostic and Statistical Manual of Diagnostic and Statistical Manual of Mental Diseases-IV Mental Diseases-IV (DSM-IV).(DSM-IV).
Inclusion Criteria: Controls
The control population consisted of all The control population consisted of all remaining subjects in the database who did remaining subjects in the database who did not have an ICD-9 code of 314.00, 314.01, not have an ICD-9 code of 314.00, 314.01, or 314.8 or the DSM-IV code of 314.9 in or 314.8 or the DSM-IV code of 314.9 in their diagnostic formulation at any time their diagnostic formulation at any time during the 2-year span of the study. There during the 2-year span of the study. There were 24.5 controls per case in this study.were 24.5 controls per case in this study.
Limitations
The validity of the diagnosis reported needs to be The validity of the diagnosis reported needs to be considered.considered. These data are from a single rural state, and the These data are from a single rural state, and the
subjects are not currently traceable across years subjects are not currently traceable across years or type of claims.or type of claims.
The data set does not include uninsured The data set does not include uninsured children or children who did not access health children or children who did not access health care in the 2-year period included in this study.care in the 2-year period included in this study.
Prevalence of ADHD by Age Group, Gender, and Payer Type
19961996 19971997 MeanMean
N (%)N (%) N (%)N (%) N (%)N (%)
Age GroupAge Group
Infant to 5 yrInfant to 5 yr 334 (1.2)334 (1.2) 190 (0.6)190 (0.6) 262 (0.9)262 (0.9)
6 to 13 yr6 to 13 yr 2952 (10.8)2952 (10.8) 2387 (6.7)2387 (6.7) 2669 (8.7)2669 (8.7)
14 to 21 yr14 to 21 yr 1031 (3.1)1031 (3.1) 851 (2.1)851 (2.1) 941 (2.6)941 (2.6)
GenderGender
MaleMale 3247 (7.5)3247 (7.5) 2570 (4.8)2570 (4.8) 2908 (6.1)2908 (6.1)
FemaleFemale 1070 (2.4)1070 (2.4) 858 (1.6)858 (1.6) 964 (2.0)964 (2.0)
Payer TypePayer Type
PublicPublic 1233 (5.8)1233 (5.8) 909 (6.0)909 (6.0) 1071 (5.9)1071 (5.9)
PrivatePrivate 3084 (4.6)3084 (4.6) 2519 (2.7)2519 (2.7) 2801 (3.6)2801 (3.6)ADHD = attention-deficit hyperactivity disorder
Results
Prevalence and Base Costs of ADHDPrevalence and Base Costs of ADHD The prevalence of ADHD in these claims The prevalence of ADHD in these claims
data was 3.9% or 7,745 children (4,317 in data was 3.9% or 7,745 children (4,317 in 1996 and 3,428 in 1997).1996 and 3,428 in 1997).
Prevalence and Risk of 4 Most Common General and Neurologic Diagnoses in Children With ADHD Compared
With Children Without ADHD (Controls)ObservedObserved ExpectedExpected AddedAdded
DiagnosisDiagnosis N (%)N (%) NN CasesCases AR%AR%
Respiratory illnessRespiratory illness
19961996 ADHDADHD
ControlControl
312 (7.2)312 (7.2)
18,672 (22.1)18,672 (22.1)
955955 -643-643 -206.2-206.2
19971997 ADHDADHD
ControlControl
267 (7.8)267 (7.8)
19,513 (18.4)19,513 (18.4)
632632 -365-365 -136.7-136.7
Acute pharyngitisAcute pharyngitis
19961996 ADHDADHD
ControlControl
271 (6.3)271 (6.3)
16,422 (19.5)16,422 (19.5)
840840 -569-569 -210.0-210.0
19971997 ADHD ADHD
ControlControl
318 (9.3)318 (9.3)
17,374 (16.4)17,374 (16.4)
563563 -245-245 -76.9-76.9
Respiratory illness: 465.xx; Acute pharyngitis: 462.xx
ADHD = attention-deficit hyperactivity disorder; AR% = attributable risk percentage
Prevalence and Risk of 4 Most Common General and Neurologic Diagnoses in Children With ADHD Compared
With Children Without ADHD (Controls)
ObservedObserved ExpectedExpected AddedAdded
DiagnosisDiagnosis N (%)N (%) NN CasesCases AR%AR%
VisionVision
1996 1996 ADHD ADHD
ControlControl
368 (8.5)368 (8.5)
5146 (6.1)5146 (6.1)
263263 105105 28.528.5
19971997 ADHD ADHD
ControlControl
181 (5.3)181 (5.3)
30,006 (2.8)30,006 (2.8)
9797 8484 46.246.2
Suppurative otitis mediaSuppurative otitis media
19961996 ADHD ADHD
ControlControl
259 (6.0)259 (6.0)
15,717 (18.6)15,717 (18.6)
804804 -545-545 -210.4-210.4
19971997 ADHD ADHD
ControlControl
235 (6.9)235 (6.9)
16,449 (15.5)16,449 (15.5)
533533 -298-298 -126.7-126.7
Vision: 367.xx; Suppurative otitis media: 382.xx
ADHD = attention-deficit hyperactivity disorder; AR% = attributable risk percentage
Comorbidity With General and Neurologic Diagnosis
PrevalencePrevalence These data identify an important These data identify an important
association between a diagnosis of association between a diagnosis of ADHD and a decrease in the total risk of ADHD and a decrease in the total risk of these comorbid conditions. This suggests these comorbid conditions. This suggests the possibility of a protective effect from the possibility of a protective effect from ADHD for several common illnesses.ADHD for several common illnesses.
Comparison of Mean Costs of Common General and Neurologic Illnesses Between Children With ADHD and Controls (Base Cost=$495, Cost Attributable to
ADHD=$154)
Mean Cost per Mean Cost per Year ($)Year ($)
ADHDADHD ControlControl
Mean CostMean Cost
Attributable ($)Attributable ($)
Mean Cost ofMean Cost of
Comorbidity ($)Comorbidity ($)
Respiratory illnessRespiratory illness
19961996
19971997
AverageAverage
14291429
837837
11331133
831831
488488
659659
222222
108108
164164
481481
159159
320320
Acute pharyngitisAcute pharyngitis
19961996
19971997
AverageAverage
13851385
789789
10871087
792792
445445
618618
183183
6565
123123
476476
153153
315315
ADHD = attention-deficit hyperactivity disorder
Comparison of Mean Costs of Common General and Neurologic Illnesses Between Children With ADHD and
Controls (Base Cost=$495, Cost Attributable to ADHD=$154)
Mean Cost perMean Cost per Year ($)Year ($)
ADHDADHD ControlControl
Mean CostMean Cost
Attributable Attributable ($)($)
Mean Cost ofMean Cost of
Comorbidity Comorbidity ($)($)
VisonVison
19961996
19971997
AverageAverage
10601060
940940
10001000
589589
402402
495495
-20-20
2222
11
354354
348348
351351
Suppurative otitis mediaSuppurative otitis media
19961996
19971997
AverageAverage
14501450
887887
11681168
838838
504504
671671
229229
124124
176176
494494
193193
343343
ADHD = attention-deficit hyperactivity disorder
Costs
The cost of care for these comorbid general health The cost of care for these comorbid general health conditions was increased.conditions was increased.
The equation for the total annual cost of care ($1133) is The equation for the total annual cost of care ($1133) is composed of:composed of: Base cost of care for a control child ($495)Base cost of care for a control child ($495) Cost of care attributable to ADHD ($154)Cost of care attributable to ADHD ($154) Cost of care attributable to respiratory illness in Cost of care attributable to respiratory illness in
controls without ADHD ($164)controls without ADHD ($164) The cost of comorbidity ($1133-$495-$154-The cost of comorbidity ($1133-$495-$154-
$164=$320).$164=$320).
Comparison of Mean Costs of Common Mental Illnesses Between Children With ADHD and Controls (Base Cost=$495, Cost Attributable to ADHD=$154)
Mean Cost Mean Cost perper
Year (%)Year (%)
ADHDADHD ControlControl
Mean CostMean Cost
Attributable (%)Attributable (%)
Mean Cost of Mean Cost of Comorbidity (%)Comorbidity (%)
DepressionDepression
19961996 15191519 10811081 586586 321321
19971997 11421142 10421042 547547 -91-91
AverageAverage 13301330 10611061 566566 115115
Oppositional Oppositional defiant disorderdefiant disorder
19961996 16641664 13661366 871871 181181
19971997 12391239 11481148 653653 -100-100
AverageAverage 14511451 12571257 762762 4040
ADHD = attention-deficit hyperactivity disorder
Comparison of Mean Costs of Common Mental Illnesses Between Children With ADHD and Controls (Base
Cost=$495, Cost Attributable to ADHD=$154)
Mean Cost Mean Cost perper
Year (%)Year (%)
ADHDADHD ControlControl
Mean CostMean Cost
Attributable (%)Attributable (%)
Mean Cost ofMean Cost of
Comorbidity (%)Comorbidity (%)
BipolarBipolar
19961996 19911991 13821382 887887 492492
19971997 14751475 12701270 775775 1515
AverageAverage 17331733 13261326 831831 253253
Conduct disordersConduct disorders
19961996 18511851 12791279 784784 454454
19971997 13021302 11401140 645645 -28-28
AverageAverage 15761576 12091209 714714 213213
ADHD = attention-deficit hyperactivity disorder
Prevalence and Risk of 4 Most Common Mental Diagnoses in Children With ADHD Compared With Children Without ADHD
DiagnosesDiagnoses
ObservedObserved
N (%)N (%)
ExpectedExpected
NN
AddedAdded
CasesCases AR%AR%
DepressionDepression
19961996 ADHDADHD
ControlControl
836 (19.4)836 (19.4)
2690 (3.2)2690 (3.2)
138138 698698 83.583.5
19971997 ADHDADHD
ControlControl
655 (19.1)655 (19.1)
2139 (2.0)2139 (2.0)
6969 586586 89.489.4
Oppositional Oppositional defiant disorderdefiant disorder
19961996 ADHDADHD
ControlControl
493 (11.4)493 (11.4)
316 (0.4)316 (0.4)
1616 477477 96.796.7
19971997 ADHDADHD
ControlControl
377 (11.0)377 (11.0)
218 (0.2)218 (0.2)
77 370370 98.198.1
Depression: 293.83, 296.2x, 296.3x, 296.5x, 296.82, 298.0x, 300.4x, 301.12, 309.0x, 309.1x, 309.28, 311.xx, and 313.1x; Oppositional defiant disorder: 3131.81
ADHD = attention-deficit hyperactivity disorder; AR%= attributable risk percentage
Prevalence and Risk of 4 Most Common Mental Diagnoses in Children With ADHD Compared With Children Without ADHD
DiagnosesDiagnoses
ObservedObserved
N (%)N (%)
ExpectedExpected
NN
AddedAdded
CasesCases AR%AR%
BipolarBipolar
19961996 ADHDADHD
ControlControl
363 (8.4)363 (8.4)
1148 (1.4)1148 (1.4)
5959 304304 83.883.8
19971997 ADHDADHD
ControlControl
270 (7.9)270 (7.9)
909 (0.9)909 (0.9)
2929 241241 89.189.1
Conduct disordersConduct disorders
19961996 ADHDADHD
ControlControl
329 (7.6)329 (7.6)
437 (0.5)437 (0.5)
2222 307307 93.293.2
19971997 ADHDADHD
ControlControl
198 (5.8)198 (5.8)
305 (0.3)305 (0.3)
1010 188188 95.095.0
Bipolar: 296.xx; Conduct disorders: 312.xx
ADHD = attention-deficit hyperactivity disorder; AR% = attributable risk percentage
Prevalence: Comorbidity With Mental and Neurologic Disorders
The relative risks of a child with ADHD being The relative risks of a child with ADHD being diagnosed with an additional mental disease diagnosed with an additional mental disease were all greater than 1, ranging from 3.2 were all greater than 1, ranging from 3.2 (nondependent drug use) to 53.4 (oppositional (nondependent drug use) to 53.4 (oppositional defiant disorder). defiant disorder).
Children with ADHD were 53 times more Children with ADHD were 53 times more likely to have oppositional defiant disorder likely to have oppositional defiant disorder than controls.than controls.
Four Disorders
Oppositional defiant disorder, conduct Oppositional defiant disorder, conduct disorders, learning disabilities, and ticsdisorders, learning disabilities, and tics Have an attributable risk percentage Have an attributable risk percentage
above 90%above 90% This suggests that ADHD represents an This suggests that ADHD represents an
important risk marker for multiple mental important risk marker for multiple mental health disorders.health disorders.
Policy Implications: Costs Attributable costs for mental disorders Attributable costs for mental disorders
ranged from $204 (tic disorder) to $1262 ranged from $204 (tic disorder) to $1262 (personality disorder).(personality disorder).
The cost of care attributable to depression The cost of care attributable to depression in a control child was $566 ($1061-$495).in a control child was $566 ($1061-$495).
The cost of comorbidity in children with The cost of comorbidity in children with ADHD and depression was $115 ($1330-ADHD and depression was $115 ($1330-$495-$154-$566=$115).$495-$154-$566=$115).
Clinical Implications
We have identified an ADHD comorbidity paradoxWe have identified an ADHD comorbidity paradox This was a decrease of 12 to 70% of the expected number This was a decrease of 12 to 70% of the expected number
of cases.of cases. In contrast, there were 26 to 698 additional cases of vision In contrast, there were 26 to 698 additional cases of vision
problems, epilepsy, depression, oppositional defiant problems, epilepsy, depression, oppositional defiant disorder, bipolar disorder, conduct disorder, adjustment disorder, bipolar disorder, conduct disorder, adjustment disorder, anxiety disorder, nondependent drug use, tic disorder, anxiety disorder, nondependent drug use, tic disorders, personality disorders, epilepsy, and visual disorders, personality disorders, epilepsy, and visual impairment.impairment.
For these illnesses, the number of observed cases was For these illnesses, the number of observed cases was increased by 97 to 5286% over the expected numberincreased by 97 to 5286% over the expected number