Mental and somatic comorbidity of depression: a comprehensive cross-sectional analysis of 202 diagnosis groups using German nationwide ambulatory claims data

Abstract

Background: Depression is frequently accompanied by other mental disorders and various somatic diseases; however, previous comorbidity studies often relied on self-reported data and have not simultaneously assessed the entire spectrum of mental and somatic diagnoses. The aim is to provide a complete picture of mental and somatic comorbidity of depression in routine outpatient care in a high income country with a relatively well equipped health care system.

Methods: Using ambulatory claims data covering 87% of the German population (age 15+), we designed a cross-sectional study by identifying persons diagnosed with mild, moderate and severe depression in 2017 (N = 6.3 million) and a control group matched 4:1 on sex, 5-year age group and region of residence (N = 25.2 million). Stratified by severity, we calculated the prevalence of 202 diagnosis groups included in the ICD-10 in persons with depression as compared to matched controls using prevalence ratios (PR).

Results: Nearly all mental disorders were at least twice as prevalent in persons with depression relative to controls, showing a dose-response relationship with depression severity. Irrespective of severity, the three most prevalent somatic comorbid diagnosis groups were 'other dorsopathies' (M50-M54), 'hypertensive diseases' (I10-I15) and 'metabolic disorders' (E70-E90), exhibiting PRs in moderate depression of 1.56, 1.23 and 1.33, respectively. Strong associations were revealed with diseases of the central nervous system (i.e. multiple sclerosis) and several neurological diseases, among them sleep disorders, migraine and epilepsy, most of them exhibiting at least 2- to 3-fold higher prevalences in depression relative to controls. Utilization of health care was higher among depression cases compared to controls.

Conclusions: The present study based on data from nearly the complete adolescent and adult population in Germany comprehensively illustrates the comorbidity status of persons diagnosed with depression as coded in routine health care. Our study should contribute to increasing the awareness of the strong interconnection of depression with all other mental and the vast majority of somatic diseases. Our findings underscore clinical and health-economic relevance and the necessity of systematically addressing the high comorbidity of depression and somatic as well as other mental diseases through prevention, early identification and adequate management of depressive symptoms.

Keywords: Ambulatory claims data; Comorbidity; Depression; Mental disorders; Somatic diseases.

Fig. 1

Selection of study participants. A hierarchical classification, considering only the most severe diagnosis, was used to define cases of mild, moderate and severe depression based on diagnostic codes documented in ambulatory care. From the group of all persons with a least one diagnosis of depression in 2017 (n = 9,827,889), cases of severe depression were defined as patients with at least one diagnosis of F32.2, F32.3, F33.2 or F33.3 (n = 1,404,250). From the remaining patients, those who had at least one diagnosis of F32.1 or F33.1 were classified as cases with moderate depression (n = 3,213,925). Finally, patients with a diagnosis of F32.0, F33.0 or F34.1 were classified to have mild depression (1,685,108). Patients who did not have at least one specific diagnostic code of depression to differentiate the severity of the disease were not included in the present analysis (n = 3,524,606). Thus, cases exclusively coded with F32.8, F32.9, F33.8 and F33.9 were not considered as cases in the present study

Fig. 2

Prevalence of mental disorders among cases with unipolar depression and prevalence ratios relative to controls. Diagnosis groups according to ICD-10: F00-F09, Organic mental disorders; F10-F19, Substance use disorders; F20-F29, Schizophrenia; F40-F48, Neurotic, stress-related and somatoform disorders; F50-F59, Behavioral syndromes associated with physiological disturbances and physical factors; F60-F69, Disorders of adult personality and behavior; F70-F79, Mental retardation; F80-F89, Disorders of psychological development; F90-F98, Behavioral and emotional disorders with onset in childhood and adolescence; F99-F99, Unspecified mental disorders. The prevalence ratio is defined as the ratio of the prevalence of the respective diagnosis group among depression cases to the prevalence among age-, sex- and region-matched controls

Fig. 3

Prevalence ratios of somatic comorbidities according to prevalence among controls by depression severity. Prevalence ratios were estimated for 191 somatic diagnosis groups from the ICD-10 based on administrative data from outpatient care including 6.3 million patients with a specific diagnosis of depression in 2017 and 25.2 million age-, sex- and region-matched controls. The prevalence ratio is defined as the ratio of the prevalence of the respective diagnosis group among depression cases to the prevalence among controls. Diagnosis groups are colored according to the respective chapter of the ICD

Fig. 4

Age-adjusted prevalence and prevalence ratios for the most prevalent comorbidities by sex . Prevalence ratios were estimated for 201 diagnosis groups from the ICD-10 reflecting mental and somatic diseases using administrative data from outpatient care including 6.3 million patients with a specific diagnosis of depression in 2017 and 25.2 million age- and sex-matched controls. Sex-specific prevalence was age-adjusted using the joint age distribution of depression cases as reference, stratified by severity. The prevalence ratio is defined as the ratio of the prevalence of the respective diagnosis group among depression cases to the prevalence among controls