Abstract
Background
Persons with intellectual disability (ID) often suffer from significant comorbidities. As data have been lacking until now, the present report is the first one containing outpatient data on the prevalence of ID in Germany, its comorbidities, and outpatient (drug) treatment.
Methods
This study is based on the nationwide outpatient billing data and drug prescription data of all SHI-insured adults (SHI, statutory health insurance) (age 18–109) who were seen at least once in an outpatient medical practice in 2018. Patients with at least two F70–F79 diagnoses in two quarters were included in the study group (SG) (n = 324 428). A random sample of patients without ID served as the control/comparison group (CG) (n = 648 856). The odds ratios (SG vs. CG) for comorbidities, prescriptions of selected classes of drugs, and involvement of medical specialties were each analyzed by multivariate logistic regression.
Results
The prevalence of ID was 0.55%. ID was found to be associated with a variety of comorbidities. The highest odds ratios [OR] were for infantile cerebral palsy (OR: 121.71; 95% confidence interval: [111.67; 132.67]), autism spectrum disorders (OR: 83.85 [75.54; 93.08]), and developmental disabilities (OR: 61.34 [58.86; 63.94]). The most frequently prescribed drug categories (as classified by the anatomic-therapeutic-chemical (ATC) convention) were psychoactive drugs (antipsychotic, anxiolytic, and hypnotic drugs and sedatives) and antiepileptic drugs (OR: 10.40 [10.27; 10.53] and 9.90 [9.75; 10.05], respectively). Both general practitioners (OR: 2.64 [2.59; 2.69]) and medical specialists were consulted by the SG more frequently than by the CG; the type of specialist most commonly consulted was in the neuropsychiatric field, i.e., a neurologist or psychiatrist (OR: 6.85 [6.77; 6.92]).
Conclusion
A diagnosis of ID frequently appears in outpatient billing data. Future analyses should be devoted to the specific care of people with intellectual disability, who constitute an especially multimorbid and vulnerable patient group.
According to a meta-analysis of international studies, 1.04% of the population are affected by intellectual disability (ID) (1). People with ID often have somatic comorbidities such as respiratory failure, malnutrition, dehydration, and cardiovascular disorders (2). As a result, their mortality is raised by a factor of 3 and their life expectancy lowered by almost 20 years (3). All studies, however, come from the international literature, are not recent, or don’t share information on what groups of doctors from the different medical specialties were involved.
The present study was carried out to obtain recent data on how common the diagnosis of ID is (International Classification of Diseases (ICD)-10, chapter V, F70–79) in Germany (primary endpoint/outcome). Secondary outcomes were the odds ratios of the neurological-psychiatric and somatic comorbidities compared with the comparison/control group (without ID), the prescribing prevalence of selected groups of medications, especially psychoactive drugs, and the participation of medical specialty groups.
Methods
We collected nationwide billing data from doctors treating adults in statutory medical insurance schemes (§295 SGB [social code] V) and drug prescribing data (§300 Section 2 SGB V) for the year 2018. These were anonymized at the level of the individual insurance member and include all diagnoses and drug prescriptions (collected prescriptions) of members of statutory health insurers who had contact with outpatient medical practices.
Study population
The study population included insurance scheme members with ID aged 18–109 years and at least two confirmed F70–79 diagnoses according to the German modification of the ICD-10 (ICD-10-GM) in two quarters of the year 2018. All insured adults included from the data source formed the denominator for calculating the prevalence of a diagnosis of ID. The control/comparison group was a random sample of all patients without ID who were treated in 2018, in a ratio of 2:1 to the study population, aged between 18 and 109 years, as an approximation to the average population. For the study population we checked which maximum severity grade of ID had been coded in the same year (F70=mild ID, F71=moderate ID, F72=severe ID, F73=profound ID).
Comorbidities
For selected comorbidities we checked for each patient in the study population and control population whether at least one confirmed diagnosis existed for 2018, and we then calculated prevalence rates.
Drug prescriptions by anatomic-therapeutic-chemical classification
To analyze drug prescriptions, we used the official anatomic-therapeutic-chemical (ATC) classification (4). For selected drug groups we checked on the basis of the third ATC level (therapeutic pharmacological subgroup), whether at least one prescription had been collected. The prescription prevalence was defined as the proportion of patients with prescriptions of all patients in the population.
Participation of medical specialty groups
As no specific specialty exists for treating people with ID, we selected the specialist groups according to general clinical experience.
According to the valid guideline of the national Association of Statutory Health Insurance physicians (KBV, Kassenärztliche Bundesvereinigung), we deducted the specialty group to which a doctor belonged from the last two digits of the nine-digit lifelong registration code (LANR) that doctors are automatically allocated when they start working as statutory health insurance physicians (as employees or in their own practice). We analyzed neurology, psychiatry, and psychotherapy (LANR groups 51, 53, 58, 60, 61), general practice (LANR 01, 02, 03), internal medicine (LANR 23), rehabilitation medicine (LANR 57), and orthopedics (LANR 10). As the study data were anonymized, we could not start out with patients, only with diagnoses. Where an F70–79 diagnosis was found, we counted on the basis of the billing data which medical specialty group made the diagnosis.
Statistical analyses and ethics approval
We used multivariable regression models to calculate odds ratios (OR) and 95% confidence intervals. Age and sex were included as covariates in all models in addition to the variable of interest, and the resulting estimates were controlled between the study population and the control population. To assess whether ORs have a substantial effect, we chose established cut-off values by Chinn (6) (OR >1.436 or <0.696). As our analysis was an initial, exploratory, hypothesis generating analysis, for which no a priori hypotheses had been formulated, we did not correct the p values for multiple tests. For this reason, we also restricted our interpretation of the odds ratios and mention the p values where appropriate for the sole purpose of orientation.
The ethics committee of the Bavarian State Medical Association assessed the study as not requiring consultation because the data were completely anonymized (No 20069 on 11 August 2020).
Results
We studied 324,428 persons with ID. For a total data set of 59,146,612 insurance holders this corresponds to a diagnostic prevalence of 0.55%. This varied by age and sex: 18–44 years: 0.61%; 45–64 years: 0.65%, older than 65 years: 0.33%; men: 0.65%; women: 0.47%). The control/comparison population included 648,856 persons and the proportion of men was smaller while the average age was older (proportion of men: study population: 53.5%, control population: 46.5%; mean age: study population 47.5 years (standard deviation=17.2 years), control population: 51.3 years (SD 19.4 years).
The severity of ID was determined for 62.7% of the study population. Of these, 24.9% had mild, 21.0% moderate, 123.1% had severe, and 4.6% profound ID.
Table 1 shows the total prevalence rates, those by age and sex, and the results of the logistic regression. For all psychiatric, neurological, and somatic comorbidities except for neoplasms, the prevalence and therefore the odds ratios were higher in the study population than in the control population.
Table 1. Prevalence of selected comorbidities in the study and control populations by indicator.
| Indicator | Prevalence (%) | Results of the multivariable logistic regression (controlled for age and sex) | ||||||||||||||
| Description or definition (ICD-10-GM) | Study population | Control population | ||||||||||||||
|
Total
(N = 324 428) |
Men | Women |
Total
(n = 648 856) |
Men | Women | |||||||||||
|
18–44 years
(n = 76 861) |
45–64 years
(n = 70 958) |
ab 65 years
(n = 26 062) |
18–44 years
(n = 63 085) |
45–64 years
(n = 59 854) |
ab 65 years
(n = 27 608) |
18–44 years
(n = 118 641) |
45–64 years
(n = 102 420) |
ab 65 years
(n = 72 562) |
18–44 years
(n = 132 539) |
45–64 years
(n = 120 150) |
ab 65 years
(n = 102 544) |
Odds ratio | 95% confidence interval | |||
| Psychiatric comorbidities | ||||||||||||||||
| Autism spectrum disorder (F84.0, F84.1, F84.5) | 5.1 | 9.9 | 4.4 | 1.7 | 5.5 | 2.8 | 0.9 | 0.1 | 0.2 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 | 83.85 | [75.54; 93.08] |
| Developmental disorders (F80–F89) | 19.3 | 32.6 | 12.3 | 6.7 | 29.3 | 11.5 | 5.9 | 0.4 | 0.9 | 0.2 | 0.2 | 0.5 | 0.1 | 0.1 | 61.34 | [58.86; 63.94] |
| Conduct disorder, childhood-onset type (F91.1) | 2.0 | 2.9 | 2.1 | 1.8 | 1.9 | 1.5 | 1.3 | 0.1 | 0.1 | 0.1 | 0.2 | 0.0 | 0.0 | 0.2 | 23.31 | [21.37; 25.44] |
| Schizophrenia, schizotypal, and delusional disorders (F20–F29) | 15.1 | 10.9 | 18.0 | 16.3 | 10.0 | 19.8 | 19.1 | 1.1 | 1.0 | 1.3 | 1.1 | 0.6 | 1.4 | 1.7 | 16.51 | [16.10; 16.93] |
| Organic, including symptomatic, mental disorders (F00–F09) | 23.9 | 14.2 | 26.4 | 43.5 | 13.5 | 25.7 | 46.1 | 3.7 | 0.3 | 1.4 | 10.7 | 0.3 | 1.0 | 12.5 | 11.57 | [11.39; 11.76] |
| Emotionally unstable personality disorder (F60.3) | 1.2 | 1.6 | 1.0 | 0.6 | 1.7 | 0.9 | 0.5 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 0.1 | 0.1 | 9.84 | [9.09; 10.65] |
| Behavioral and emotional disorders with onset usually occurring in childhood and adolescence (F90–F98) | 9.6 | 17.4 | 6.8 | 4.9 | 11.7 | 5.4 | 3.9 | 1.0 | 2.1 | 0.6 | 0.6 | 1.0 | 0.6 | 0.7 | 9.45 | [9.19; 9.71] |
| Disorders of adult personality and behavior (F60–F69) | 15.9 | 15.8 | 16.1 | 13.4 | 17.6 | 16.4 | 12.7 | 2.1 | 1.8 | 2.1 | 1.5 | 2.6 | 2.6 | 1.7 | 8.68 | [8.51; 8.85] |
| Affective disorders (F30-F39) | 23.0 | 16.4 | 20.9 | 21.0 | 23.3 | 30.7 | 31.5 | 16.7 | 8.7 | 15.0 | 14.4 | 13.4 | 24.0 | 25.3 | 1.66 | [1.64; 1.68] |
| Mental and behavioral disorders due to psychoactive substance use (F10-F19) | 12.1 | 9.8 | 19.1 | 18.3 | 6.9 | 11.3 | 7.8 | 8.7 | 7.6 | 15.0 | 9.8 | 5.7 | 9.8 | 5.6 | 1.43 | [1.41; 1.45] |
| Reaction to severe stress, and adjustment disorders (F43) | 10.8 | 11.4 | 8.2 | 4.6 | 16.6 | 12.0 | 6.3 | 8.0 | 5.9 | 6.9 | 3.5 | 10.5 | 12.3 | 6.3 | 1.41 | [1.39; 1.43] |
| Behavioral syndromes associated with physiological disturbances and physical factors (F50–F59) | 4.3 | 3.7 | 4.2 | 4.6 | 5.3 | 4.3 | 3.9 | 4.1 | 2.2 | 6.0 | 8.9 | 3.2 | 3.7 | 2.9 | 1.07 | [1.05; 1.09] |
| Neurological comorbidities | ||||||||||||||||
| Infantile cerebral palsy (G80) | 9.5 | 11.8 | 8.1 | 4.9 | 12.4 | 8.9 | 5.0 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 | 121.71 | [111.67; 132.67] |
| Epilepsy (G40–G41) | 26.5 | 28.8 | 27.8 | 19.3 | 28.6 | 26.9 | 17.9 | 1.4 | 1.0 | 1.6 | 2.2 | 0.9 | 1.2 | 2.0 | 24.97 | [24.42; 25.53] |
| Hydrocephalus (G91) | 1.9 | 2.6 | 1.5 | 1.1 | 2.5 | 1.4 | 1.0 | 0.1 | 0.1 | 0.1 | 0.3 | 0.1 | 0.1 | 0.2 | 16.39 | [15.16; 17.72] |
| Hemiplegia and hemiparesis, paraparesis/paraplegia, tetraparesis/tetraplegia (G81, G82) | 10.9 | 11.2 | 10.5 | 10.4 | 11.7 | 10.8 | 9.6 | 1.2 | 0.3 | 1.2 | 3.3 | 0.3 | 0.9 | 2.6 | 10.11 | [9.86; 10.36] |
| Extrapyramidal symptoms in the absence of parkinsonism (G21-G25) | 5.5 | 3.9 | 5.8 | 8.2 | 3.9 | 6.3 | 9.1 | 2.0 | 0.5 | 1.4 | 3.7 | 0.5 | 2.0 | 5.3 | 3.27 | [3.19; 3.35] |
| Somatic comorbidities | ||||||||||||||||
| Symptoms and signs involving the nervous and musculoskeletal systems (R25–R29) | 18.5 | 13.2 | 15.6 | 32.2 | 14.7 | 18.3 | 37.4 | 6.7 | 1.4 | 2.8 | 16.2 | 1.6 | 3.2 | 20.9 | 4.12 | [4.06; 4.18] |
| Hypovolemia (E86) | 1.1 | 0.5 | 0.9 | 3.0 | 0.5 | 1.0 | 3.4 | 0.5 | 0.2 | 0.2 | 1.1 | 0.2 | 0.2 | 1.6 | 2.81 | [2.68; 2.95] |
| Respiratory failure, not elsewhere classified (J96) | 1.3 | 0.6 | 1.5 | 3.0 | 0.6 | 1.4 | 2.2 | 0.8 | 0.1 | 0.8 | 2.6 | 0.1 | 0.6 | 1.7 | 1.76 | [1.69; 1.83] |
| Diseases of the circulatory system (I00–I99) | 50.7 | 27.3 | 58.9 | 82.5 | 30.7 | 62.2 | 85.7 | 47.5 | 15.0 | 53.1 | 85.9 | 18.2 | 51.5 | 85.6 | 1.63 | [1.61; 1.64] |
| Certain infectious and parasitic diseases (A00–B99) | 33.0 | 34.9 | 29.3 | 29.0 | 38.4 | 32.5 | 29.4 | 25.0 | 30.7 | 21.7 | 19.9 | 30.7 | 23.4 | 19.9 | 1.42 | [1.41; 1.44] |
| Diseases of esophagus, stomach, and duodenum (K20–K31) | 17.5 | 13.2 | 19.1 | 24.4 | 14.0 | 19.1 | 23.9 | 16.1 | 9.9 | 16.7 | 23.1 | 9.8 | 17.1 | 25.1 | 1.21 | [1.19; 1.22] |
| Pain, unspecified (R52) | 9.1 | 4.5 | 8.7 | 14.4 | 6.1 | 11.3 | 19.8 | 9.4 | 3.1 | 8.2 | 13.6 | 4.0 | 10.8 | 20.1 | 1.14 | [1.12; 1.15] |
| Neoplasms (C00–C97) | 5.1 | 1.5 | 4.6 | 14.1 | 1.6 | 6.4 | 13.3 | 8.3 | 0.9 | 5.5 | 24.9 | 1.4 | 7.5 | 18.0 | 0.71 | [0.70; 0.72] |
Substantial effect sizes or odds ratios are rendered in bold. Because of complete anonymization we could not investigate the extent to which patients had more than one disorders. All p values were below 0.0001. As our study was an exploratory analysis, we did not determine the goodness of fit of the model. ICD-10-GM, German modification of the International Classification of Diseases 10.
The psychiatric odds ratios in the study population were highest for autism spectrum disorders (83.85) and developmental disorders (61.34). Substantial effect sizes (OR>1.436) were also observed for the groups of personality disorders and social-behavioral disorders (F60–69: OR=8.68; F91: OR=23.31) and for emotionally unstable personality disorder (F60.3: OR=9.84). We did not observe substantial effect sizes in substance abuse disorder (OR=1.42), adjustment disorder (OR=1.41) or behavioral disorders secondary to somatic disorders (OR=1.07).
All neurological comorbidities under study were associated with a higher probability in patients with ID. The highest odds ratios in this context were seen for infantile cerebral palsy (OR=121.71) and epilepsy (24.97). Substantial effects were also seen for hydrocephalus (OR=16.39), palsies (OR=10.11), and extrapyramidal symptoms (OR=3.27). Similarly, the prevalence rates of all somatic comorbidities under study were higher in the study population than in the control population. However, the relevant/respective odds ratios were as a rule lower in both populations than those of neuropsychiatric disorders. The largest odds ratios were seen for symptoms that affect the nervous system or the movement apparatus (OR=4.12) and for hypovolemia (OR=2.81). No substantial effect sizes were seen for infectious diseases, disorders of the esophagus, stomach, and duodenum, and for pain. Neoplasms were rarer (by 29%) in the study population compared to the control population.
Table 2 shows the results of the multivariable logistic regression for selected drug groups for the total population as well as grouped by age and sex in the study and control populations per indicator.
Table 2. Prevalence of medication prescriptions and treatment by doctors from selected medical specialty groups in the study and control populations in 2018 and results of the multivariable logistic regression.
| Indicator | Prevalence of prescriptions or treatments (%) | Results of the multivariable logistic regression (controlled for age and sex) | ||||||||||||||
| Description or definition (ATC or LANR) | Study population | Control population | ||||||||||||||
|
Total
(N = 324 428) |
Men | Women |
Total
(n = 648 856) |
Men | Women | |||||||||||
|
18–44 years
(n = 76 861) |
45–64 years
(n = 70 958) |
ab 65 years
(n = 26 062) |
18–44 years
(n = 63 085) |
45–64 years
(n = 59 854) |
ab 65 years
(n = 27 608) |
18–44 years
(n = 118 641) |
45–64 years
(n = 102 420) |
ab 65 years
(n = 72 562) |
18–44 years
(n = 132 539) |
45–64 years
(n = 120 150) |
ab 65 years
(n = 102 544) |
Odds ratio | 95% confidence interval | |||
| Drug prescriptions | ||||||||||||||||
| Antipsychotic drugs (N05) | 38.8 | 36.2 | 42.9 | 39.6 | 31.6 | 43.1 | 42.4 | 6.4 | 2.7 | 5.2 | 9.8 | 2.8 | 6.8 | 14.0 | 10.40 | [10.27; 10.53] |
| Antiepileptic drugs (N03) | 26.9 | 27.6 | 29.1 | 21.5 | 26.5 | 28.8 | 20.6 | 3.7 | 1.3 | 3.5 | 6.8 | 1.4 | 3.7 | 7.6 | 9.90 | [9.75; 10.05] |
| Antipsychotic drugs or psychoanaleptic drugs (N05 or N06) | 47.1 | 42.5 | 49.7 | 47.7 | 40.1 | 53.9 | 54.2 | 13.9 | 6.3 | 11.8 | 17.2 | 7.8 | 17.3 | 26.7 | 6.48 | [6.41; 6.55] |
| Antiparkinson drugs (N04) | 4.7 | 2.8 | 6.0 | 8.4 | 2.1 | 5.4 | 7.7 | 1.4 | 0.2 | 0.8 | 3.3 | 0.2 | 1.1 | 3.7 | 4.23 | [4.12; 4.35] |
| Psychoanaleptic drugs (N06) | 20.7 | 15.4 | 19.4 | 19.9 | 19.3 | 27.4 | 28.1 | 10.5 | 4.8 | 9.1 | 11.2 | 6.5 | 14.2 | 18.9 | 2.52 | [2.49; 2.55] |
| Medications for functional gastrointestinal impairments (A03) | 4.5 | 4.1 | 3.7 | 4.0 | 5.5 | 4.8 | 5.4 | 3.1 | 2.4 | 2.1 | 3.0 | 3.2 | 3.4 | 4.6 | 1.54 | [1.51; 1.58] |
| Thyroid treatment (H03) | 16.3 | 9.1 | 11.0 | 12.6 | 18.3 | 26.7 | 26.7 | 14.3 | 2.6 | 6.5 | 11.1 | 12.1 | 23.9 | 29.8 | 1.41 | [1.39; 1.43] |
| Analgesics (N02) | 20.6 | 13.1 | 18.8 | 29.6 | 17.2 | 23.7 | 38.1 | 19.0 | 9.9 | 16.9 | 26.0 | 12.0 | 19.9 | 34.8 | 1.27 | [1.25; 1.28] |
| Muscle relaxants (M03) | 3.4 | 3.5 | 3.5 | 2.7 | 3.7 | 3.7 | 2.7 | 2.8 | 2.3 | 3.2 | 2.2 | 2.5 | 4.0 | 2.5 | 1.25 | [1.22; 1.28] |
| Antiemetics (A04) | 0.4 | 0.4 | 0.3 | 0.5 | 0.4 | 0.5 | 0.5 | 0.4 | 0.1 | 0.4 | 0.9 | 0.2 | 0.5 | 0.7 | 1.17 | [1.09; 1.25] |
| Calcium channel blockers (C08) | 8.4 | 2.6 | 10.3 | 19.0 | 2.0 | 9.4 | 22.0 | 9.6 | 1.2 | 9.8 | 23.2 | 0.6 | 6.9 | 24.1 | 1.07 | [1.05; 1.09] |
| Anti-inflammatory and antirheumatic drugs (M01) | 21.8 | 19.8 | 21.7 | 18.0 | 23.4 | 25.1 | 19.9 | 25.9 | 21.6 | 31.0 | 25.7 | 19.1 | 30.7 | 29.1 | 0.82 | [0.81; 0.83] |
| No prescriptions of the above substances | 18.5 | 26.9 | 15.7 | 12.4 | 24.7 | 12.0 | 7.9 | 20.8 | 26.1 | 21.8 | 15.8 | 29.3 | 17.8 | 10.0 | 0.78 | [0.77; 0.78] |
| Participation in treatment | ||||||||||||||||
| Neurology. psychiatry. psychotherapy (51. 53. 58. 60. 61) | 46.5 | 44.2 | 49.4 | 41.8 | 44.3 | 51.9 | 43.7 | 12.0 | 6.5 | 11.6 | 14.6 | 8.9 | 15.5 | 16.9 | 6.85 | [6.77; 6.92] |
| General medicine (01. 02. 03) | 95.7 | 94.4 | 96.2 | 96.8 | 94.8 | 96.8 | 97.3 | 90.1 | 88.9 | 91.7 | 94.7 | 83.9 | 90.0 | 94.8 | 2.64 | [2.59; 2.69] |
| Rehabilitation medicine (57) | 1.7 | 1.6 | 1.5 | 1.7 | 2.0 | 1.8 | 2.0 | 1.6 | 1.0 | 1.5 | 1.5 | 1.2 | 2.4 | 2.1 | 1.14 | [1.11; 1.18] |
| Orthopedics (10) | 21.0 | 19.1 | 18.8 | 15.0 | 24.6 | 25.4 | 20.3 | 22.6 | 16.6 | 23.1 | 21.4 | 16.8 | 29.6 | 29.0 | 0.96 | [0.95; 0.97] |
| Internal medicine (23) | 18.1 | 13.5 | 20.0 | 24.6 | 15.8 | 20.1 | 21.3 | 23.7 | 10.3 | 25.5 | 42.6 | 13.0 | 25.7 | 35.5 | 0.78 | [0.77; 0.79] |
| None of the above medical specialties (without 10. 23. 57) | 36.3 | 40.3 | 34.4 | 38.5 | 37.5 | 31.0 | 37.6 | 55.6 | 71.0 | 53.4 | 41.6 | 68.1 | 48.2 | 42.2 | 0.41 | [0.40; 0.41] |
Substantial effects sizes and odds ratios are rendered in bold type. Because of the complete anonymization we were not able to investigate the extent to which patients had several disorders. All p values were below 0.0001. As ours was an exploratory analysis we did not determine the goodness of fit of the model. ATC; anatomical therapeutic chemical classification; LANR,. the nine-digit lifelong registration code that doctors are automatically allocated when they start working as statutory healthinsurance physicians.
No substantial effect sizes were observed for antiemetics, calcium channel blockers, thyroid medications, anti-inflammatories, anti-rheumatic drugs, muscle relaxants, and analgesics. All other medication groups were prescribed to a great degree in patients with ID.
The odds ratios were highest for psychoactive drugs (10.4; including, among others, antipsychotic drugs, anxiolytics, hypnotics, and sedatives), antiepileptic drugs (9.9), and psychoanaleptics (2.5; primarily antidepressants). 18.5% of the study population and 20.8% of the control population did not receive any of the medications listed in Table 2 (OR=0.78 [0.77; 0.78] p<0.0001).
The greatest participation rates in treatment and therefore substantial effects in the study population applied to general practice (95.7%, OR=2.64) and the neuropsychiatric specialties, including neurology, psychiatry, and psychotherapy(46.5%, OR=6.85). Treatment participation rates of the specialties orthopedics and internal medicine were 21.0% and 18.1%. In this setting, patients with ID attended outpatient practices less often than did patients without ID, but the effect size was not substantial.
36.3% of patients with ID did not take advantage of treatment by specialists (control population: 55.6%; OR=0.41 [0.40; 0.41]; p < 0.0001).
Discussion
The present study investigated how many people diagnosed with intellectual disability presented in outpatient care, which comorbidities were present, which medications were prescribed, and which medical specialty was involved in treating such patients.
The main result of the diagnostic prevalence of ID of 0.55% in 2018 was below the rate of 1.04% reported in a meta-analysis of international population based studies (1). In the cited study, however, diagnoses of ID were much more common in low and middle income countries than in those with high income standards. Furthermore, the prevalence rose in children and adolescents if standardized psychological tests were used, such as was the case in the comparison analysis (1). We can therefore assume that the prevalence in Germany is below the international average. Possible explanations for why in our study the prevalence might be subject to an underestimate are a subjectively satisfactory quality of life and needs-based healthcare services for people with disabilities, which make a visit to the doctor unnecessary or only rarely required. Similarly, however, barriers, underdiagnosis, and poor care are also possible, in spite of the common comorbidities.
It is certain that a mild intellectual disability was in many cases not documented because it is not always relevant, depending on the reason treatment is being sought. This underreporting does, however, limits our data basis.
The data analyzed here come from statutory health insurers and represent the majority of the German population. For Germany’s private health insurance (PKV), which accounts for 10% of all people with health insurance, no comparable evaluation exists (personal communication of the association of private health insurers). As most of those with private health insurance are self employed or civil servants (7), this group can be assumed to include very few patients with ID. This might facilitate an overestimate of the prevalence of ID in Germany.
We are aware that comorbidities in the neuropsychiatric setting are statistical. Organic/physical/somatic brain injury is to be considered the cause of ID, whose consequence or symptoms can be a behavioral disorder.
This, among other factors, explains the high proportion of accompanying mental symptoms in our study. In international studies the range was 30–50% (8). In the meta-analysis reported by Mazza et al, the rate of mental comorbidities was 33.6% [25.2%; 43.1%]) (9). In the present study, almost one in four patients with ID had an affective disorder and another 15.1% a psychotic disorder. These rates seem high, as in the Mazza meta-analysis they were only 12.2% in total for depression and anxiety (6.7% and 5.5%, respectively) and 8.7% in total for schizophrenia and unspecific psychotic disorders (4.8% and 3.9%, respectively). In this setting, the high participation rates of neurologists and psychiatrists or high rates of inpatients may be explanatory factors, in addition to fundamental problems with describing the symptom spectrum “intellectual disability.” A similar problem of apparent comorbidity may apply to behavioral disorders, which in our study were coded to different F chapters (for example, F59 [Unspecified behavioral syndromes associated with physiological disturbances and physical factors] and F63 [Habit and impulse disorders]; as an additional code to F70–73 in the context of symptomatic diagnosis or to F92 [Mixed disorders of conduct and emotions]). Had there been an option for coding comorbid behavioral disorders it is likely that their proportion would have been higher.
The highest odds ratios for somatic comorbidities were for musculoskeletal problems (OR=4.12) and hypovolemia (OR=2.81). The first effect is probably the result of the usually concomitant orthopedic-physical disability. The latter problem could be due to the care situation in nursing homes, especially the problem of providing the patients with sufficient amounts of drinking fluids. Respiratory failure deserves special attention. The risk for this was increased in the study population compared with the control population and might explain the higher mortality (10).
Neoplasms were rarer in the study population. In our opinion, these are underrepresented or their symptoms are not adequately described, as other population based studies indicate higher cancer rates and mortality (11, 12). The lower proportions of antihypertensive and anti-inflammatory drugs in the study population would therefore be explained analogously.
The highest odds ratios for neurological and mental disorders in ID were for infantile cerebral palsy (OR=121.71) and developmental disorder (OR=61.34), which is probably due to a co-coding effect for ID.
95.7% of patients with ID had contact to general practitioners; 46.5% to neurologists, psychiatrists, or psychotherapists. Further specialties that were involved were orthopedics (21.0%) and internal medicine (18.1%). When we selected the medical specialties to be analyzed we assumed that no specialized qualification exists in German for ID (13). It was not know thus far which medical specialties are approached by people with ID in Germany. Our clinical experience shows that general practice is the most likely primary contact point, followed by the neurological-psychiatric specialty group (14).
The present study confirmed our assumption. As far as we are aware, however, no international references or options for comparison exists for this finding.
As far as we know, no community based healthcare structures or studies exist in Germany, unlike in some Scandinavian countries. The Healthy Ageing and Intellectual Disability Study has been investigating since 2008 which specific health factors and challenges are seen in ageing persons with ID (15).
In our study, it was not possible methodologically to determine the total number of contacts between doctors and patients; the consequence is that the exact proportions and numbers of contacts cannot be quantified, which constitutes a further limitation of our study. Assuming that in Germany, some 55,000 general practitioners look after 324,000 people with ID (16), this means that each of these doctors delivers care for six ID patients. The smaller group of neurologists, psychiatrists, and psychoanalysts (6180) delivers care to an average of 52 patients with ID. We assume that this is a reflection of the specialist neuropsychiatric inpatient care that is usual practice in many regions.
With regard to the prescription prevalence, 38.8% of prescriptions issued for ID were for psychoactive drugs. We are aware that the ATC classification (4) is not consistent with the current terminology. According to the traditional drug prescribing analyses we can assume that 55% of all prescriptions from this ATC code (that is, 21.3% of all medical drugs) were for antipsychotics, a further 19% for anxiolytic drugs, and 25% for hypnotic drugs or sedatives (17). The distribution in ID may, however, be different. What remains unknown is why and by whom these medications are prescribed/used. One possibility is the treatment of psychotic symptoms, but also agitation and behavioral disorders or challenging behaviors, which these drugs have been approved for (for example, risperidone, promethazine, or melperone) and which is guideline conform (18).
A more differentiated analysis of the subgroups of antipsychotic drugs would be highly desirable, which unfortunately was methodologically not possible for us. For the same reason, we were not able to allocate the prescriptions to a medical specialty unequivocally.
Bibliographical references regarding prescriptions of psychotropic drugs for ID naturally vary. Bowring et al (19) reported that 37.7% of patients were being treated with psychoactive drugs, whereas Doan et al (20) reported 35.0%. Both these rates are some 10% below the rate in the present study, of 47.1%, whereas antipsychotic prescriptions between the two studies are not that different (21.9% ([19] and 20.5% [20] versus 21% in our study). Overall the results are comparable only to a limited degree, depending on how exactly psychoactive drugs are defined.
The billing data used are subject to the limitation that administrative prevalence rates over two quarters are bound to be less valid than standardized diagnostic evaluation. We were not able to consider the results of intelligence tests in our study design. ICD-10 allows classification of ID from mild to profound with chapters F70–73. By adding a fourth digit to these codes the degree of behavioral disorder can be specified, which suffices for most clinical assessments. The guideline of the Association of the Scientific Medical Societies in Germany on intellectual disability (18) provides an excellent overview of diagnostic evaluation and treatment. It discusses explicitly the potential of antipsychotic drugs to influence behavioral disorders without ignoring the associated risks. We cannot judge/gauge in this setting the extent to which the guideline is adhered to. In our view, the greatest healthcare gap consists in finding sufficiently qualified nursing staff, who are able to balance the risks and benefits appropriately when administering antipsychotic drugs.
Conclusions
Our results reflect the outpatients care context of the population with ID quite well. There are bound to be service gaps, starting with training/education and continuing education all the way to assessment (21), diagnostic evaluation, and cross-sectoral cooperation (22). The extent to which gaps in the German healthcare services can be filled by means of pilot projects such as medication management and screening in patients with ID (23) or by means of the already established medical centers for adults with disabilities remains to be seen.
Acknowledgments
Translated from the original German by Birte Twisselmann, PhD.
Footnotes
Conflict of interest statement
Prof Weih is a member of the Professional Association of German Specialists in Neurology and Psychiatry and treats people with ID as a contract/panel physician. The remaining authors declare that no conflict of interest exists.
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