FLORENCE, Italy — Individuals diagnosed with schizophrenia have a high and persistent risk for subsequent substance use or mood disorders, results of a large population-based study show.
Investigators found that compared to the general population, persons who had been diagnosed with schizophrenia were four times more likely to develop a substance use disorder and were more than 2.5 times more likely to develop a mood disorder.
Although the risk for a second diagnosis is highest within 6 months of the initial schizophrenia diagnosis, these patients are still more than twice as likely as individuals in the general population to develop a substance use or mood disorder up to 15 years later.
The study was presented here at the Schizophrenia International Research Society (SIRS) 2018 Biennial Meeting.
Bidirectional Relationship
The findings are part of a wider project examining potential connections between all mental health disorders in the Danish population. To date, the research has revealed that all disorders are similarly interconnected and that long-term risks are increased, similar to those observed in patients with schizophrenia.
Study researcher Oleguer Plana Ripoll, PhD, National Center for Register-based Research, Aarhus University, Denmark, said the results show “comorbidity is pervasive.”
He added that almost all associations were statistically significant and that “all disorders were associated with almost all disorders” in a bidirectional relationship. “Not only does A increase B, but B also increases A,” he said.
“Some of the absolute risks were quite high, especially some age- and sex-specific absolute risks, which might have clinical utility to identify patients at high risk of comorbid disorders,” Ripoll said.
He noted that a number of population-based surveys suggest that mental health patients have a high risk of developing comorbidities.
However, he noted that such studies have potential limitations, such as selection biases, whereas register-based studies are typically limited to a subset of disorders and have different methodologies and involve different populations.
To examine mental health comorbidity in comprehensive range of disorders, the team gathered data on all 5,940,778 individuals living in Denmark between 2000 and 2016. The researchers linked those individuals’ civil registration numbers to the Danish Psychiatric Register, yielding a total of 83.9 million person-years of follow-up.
They classified mental health disorders into 10 main groups: organic mental disorders, substance use disorders, schizophrenia spectrum disorders, mood disorders, neurotic disorders, eating disorders, personality disorders, mental retardation, pervasive developmental disorders, and behavioral and emotional disorders.
For the current analysis, they focused on schizophrenia spectrum disorders. They examined the associations with substance use disorders and mood disorders and calculated hazard ratios on multivariate analysis that took into account age, sex, calendar time, and other psychiatric comorbidity.
Between 2000 and 2016, 21,909 men and 20,106 women were diagnosed with schizophrenia spectrum disorder.
Patients diagnosed with schizophrenia had an increased risk of being diagnosed with a subsequent substance use disorder compared with the general population (hazard ratio [HR], 4.4 overall, 4.7 for men, and 3.9 for women).
The risk highest was in the first 6 months (HR, 31.8), although schizophrenia patients were still more likely than the general population to be diagnosed with a substance use disorder even 15 years later (HR, 3.2).
Overall, 23.8% of men and 10.6% of women who were diagnosed with schizophrenia were diagnosed with a substance use disorder within 10 years.
Schizophrenia patients were also more likely than the population to be subsequently diagnosed with a mood disorder than were members of the general population (HR, 2.7 overall for both men and women).
The same time trend was observed, with individuals being at risk highest within 6 months of a schizophrenia diagnosis (HR, 18.8). At 15 years, the HR decreased to 2.3.
The 10-year rate of mood disorder diagnosis among schizophrenia patients was 15.1% for men and 20.8% for women.
“In this case, the proportion of women who will develop mood disorders is higher than the proportion of men who develop mood disorders basically because, in the source population, it is also higher,” Ripoll observed.
In a discussion after the presentation, Ripoll said that the high risk for subsequent diagnoses among schizophrenia patients within 6 months can be partly explained by the fact that a number of patients received two diagnoses on the same day.
“One of the next steps we want to do is to describe this: how many diagnoses, which diagnoses people receive, and the time between the two diagnoses. But the association that we see 15 years later? This has to be something else,” he said.
These findings are just part of the overall study. The investigators plan to launch a website in which the data describing the bidirectional relationships between all 10 groups of mental health disorders will be published in their entirety.
He explained that the site, called the NB-COMO Project, will be available to all and will be highly interactive. Through a series of charts and graphs, users will able to explore each mental disorder group in turn, examine the nature and extent of its relationship with other groups, and drill down into the data within each group.
“Fantastic Resource”
Session Chair Fiona Gaughran, MD, PhD, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, United Kingdom, who was not involved in the study, said that the Web site will be “a fantastic resource.”
She told Medscape Medical News that it will allow the community “to be able to understand the complexity with which patients present when they have a mental health condition.
“I’m interested in patients with schizophrenia in particular, but patients with schizophrenia suffer from lots of other mental health disorders, as well as physical health disorders,” she added.
“To be able to get somebody as well as they can be, it’s really important that we identify that and give people the best care for everything that ails them, so that they have the best chance of living a healthy and happy life.”
No funding for the study has been disclosed. The investigators have disclosed no relevant financial relationships.
Schizophrenia International Research Society (SIRS) 2018 Biennial Meeting. Abstract 05.3, presented April 7, 2018.
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