“To our knowledge, this is the first study to provide a comprehensive set of age- and sex-specific estimates of absolute risks associated with comorbid mental disorders,” lead author Oleguer Plana-Ripoll, Ph.D., of Aarhus University and colleagues wrote. “Our findings provide new insights into the complex nature of comorbidity, and the comprehensive nature of the analysis will provide an important foundation for future research.”
Plana-Ripoll and colleagues used health registry data from all individuals born in Denmark and residing in the country between 2000 and 2015; this encompassed 5.94 million individuals and about 84 million years of medical data. They grouped all ICD diagnoses within 10 categories of mental illness: behavioral disorders, developmental disorders, eating disorders, intellectual disability, mood disorders, neurotic disorders, organic disorders (for example, dementia), personality disorders, schizophrenia disorders, and substance use disorders. Next, they calculated the risks of an individual having a disorders within any two separate categories.
Overall, the presence of comorbidity was pervasive, with some categories of disorders having exceptionally strong odds of occurring together. For example, compared with an individual not diagnosed with a mental disorder, an individual diagnosed with a mood disorder was 30 times more likely to be diagnosed later with a personality disorder or a developmental disorder, and 20 times more likely to be diagnosed with schizophrenia or a substance use disorder.
The investigators also found that the risk of being diagnosed with a second mental illness is highest in the first six months after the diagnosis of the first disorder, and the increased risk persists for at least 15 years after the initial diagnosis.
Given this vast amount of data, the researchers developed an interactive visualization tool highlighting these various connections, which they hoped would assist clinicians in monitoring potential emerging comorbidity over time.
For related information, see the Psychiatric News article “Study Examines Connections Between Psychiatric, Neurological Disorders.”