Although obsessive-compulsive disorder (OCD) and schizophrenia are two distinct conditions, past studies have suggested there is an overlap between them.
The research team, led by Sandra M. Meier, PhD, of the Aarhus University in Denmark, notes that both conditions have similar prevalence rates, for example, and onset of both tends to occur in adolescence or early adulthood.
In addition, they say past research has indicated there are significant similarities in the pathophysiology of OCD and schizophrenia.
“Hence,” they add, “it is no surprise that obsessive-compulsive and schizophrenic symptoms coexist in a greater proportion of patients than would be expected by chance.” They point to a meta-analysis revealing that 23% of patients with schizophrenia also had OCD.
However, the researchers say few studies have investigated the long-term association between these two disorders.
With this in mind, Meier and her team investigated the association between OCD and schizophrenia by analyzing data from Danish national registers involving more than 3 million people born between 1955 and 2006. Follow-up took place from 1995 until 2012.
Phenotypes of OCD, schizophrenia ‘more common than currently acknowledged’
Of the 16,231 individuals who developed schizophrenia, the researchers found that 447 (2.75%) had a prior OCD diagnosis. In addition, of the 30,556 people who developed a schizophrenia spectrum disorder - defined as having one or more of the symptoms associated with schizophrenia - 700 (2.29%) had a prior OCD diagnosis.
According to the researchers, their findings suggest that a previous diagnosis of OCD may be linked to an increased risk of developing schizophrenia late in life. Furthermore, the team found there was even an increased risk of schizophrenia among individuals whose parents were diagnosed with OCD.
These findings remained even after controlling for other factors that may influence schizophrenia risk, such as psychiatric history and family history of psychiatric disorders.
But despite the suggestion that OCD shares many etiological factors with schizophrenia and schizophrenia spectrum disorders, the team says this does not necessarily mean the conditions should be combined as one global diagnosis.