OCD and schizophrenia are distinct and infrequently overlapping disorders. But some studies have suggested higher rates of co-existing illness with the two disorders in patients.
How the Study Was Conducted:
The authors assessed the potential relationship between the two disorders using data from Danish registers. A total of 3 million people born between 1955 and 2006 were followed up from 1995 through 2012. The authors used incidence rate ratios (IRRs) as a measure of relative risk.
A total of 16,231 people developed schizophrenia and 447 (2.75 percent) of them had a prior diagnosis of OCD. A total of 30,556 people developed a schizophrenia spectrum disorder and 700 (2.29 percent) of them had a prior OCD diagnosis. The data suggest a prior diagnosis of OCD was associated with an increased risk of developing schizophrenia (IRR=6.90) and schizophrenia spectrum disorders (IRR=5.77) later in life. The children of parents diagnosed with OCD also had an increased risk of developing schizophrenia (IRR=4.31) and schizophrenia spectrum disorders (IDD=3.10).
"Despite the fact that our results indicate putative overlapping etiological factors of OCD and schizophrenia or schizophrenia spectrum disorders, they do not necessarily suggest that these disorders should be aggregated into one global diagnosis." However, given these findings and the fact that OCD and schizophrenia co-occur with one another at a higher rate than would be expected in the general population, the phenotypes of these disorders are potentially more similar than currently acknowledged. "... Further research is needed to disentangle which genetic and environmental risk factors are truly common to OCD and schizophrenia or schizophrenia spectrum disorders."