Diseases prevalent before major depressive disorder diagnosis: an exploratory nested case–control study using health insurance-based claims data

OBJECTIVES: Major depressive disorder (MDD) is often comorbid with other chronic and/or serious diseases. However, little is known about the prevalence of various diseases that are present before MDD onset. We examined the prevalence of all pre-existing diseases in the 12 months before an MDD diagnosis. DESIGN: Exploratory nested case–control study. SETTING: Data, including diagnoses based on International Statistical Classification of Diseases and Related Health Problems, 10th revision codes, were from a Japanese health insurance database (JMDC). PARTICIPANTS: Adults newly diagnosed with MDD during 2015, 2016 or 2017 (but not the preceding year) (cases) were matched (exact) 1:10 to controls by age, sex, index date and working status. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was the proportion of patients in each group with each pre-existing disease during the 12 months before the index date (ie, before MDD diagnosis in cases). Odds ratios (ORs) for onset of MDD were calculated for each pre-existing disease. A post hoc multivariate analysis examined interactions of metabolic risk factors (diabetes, hypertension, dyslipidaemia), psychiatric disorders (sleep disorders, psychiatric disorders other than depression) and MDD-related symptoms (headache, pain, autonomic nerve imbalance) on MDD diagnosis. RESULTS: There were 13 420 cases and 134 200 controls (mean age 41.9 years; 66.5% male). The prevalence of almost all pre-existing diseases was higher in cases than in controls. The highest ORs (5.8–21.0) were for psychiatric diseases and sleep disorders. Insomnia (21.1% of patients; OR 8.7) and neurosis (9.7%; OR 10.6) were particularly prevalent in the case group. The odds of MDD increased in the presence of metabolic risk factors, psychiatric disorders and/or MDD-related symptoms. CONCLUSIONS: There is a high prevalence of pre-existing diseases in Japanese patients who develop MDD compared with matched controls without MDD. These results suggest that patients with chronic and/or serious diseases should be actively monitored for depression.