Study Looks at Association Between OCD, Schizophrenia

Athough OCD and schizophrenia are quite different in their classic forms, each can take on characteristics of the other. Obsessive-compulsive symptoms, particularly aggressive ones, can often occur during schizophrenia’s prodromal stages before the disease fully manifests. Meanwhile, while people with OCD usually are aware that their actions are irrational, some patients have little or no insight into their condition, creating the appearance of delusion.

A new prospective analysis of over 3 million people in Denmark proposes that OCD may be a risk factor for schizophrenia. This study, published September 3 in JAMA Psychiatry, found that a prior psychiatric diagnosis of OCD was associated with approximately a fivefold increased risk of developing schizophrenia.

Of the more than 16,000 people who were diagnosed with schizophrenia during the course of the study, 2.7 percent had a previous diagnosis of OCD. When the diagnosis was broadened to include any schizophrenia spectrum disorder, the increased risk was still significant, with 2.3 percent of cases having a previous OCD diagnosis.

Risk was also increased even if an individual did not have OCD, but his or her mother or father did. “We tested the relative risk of several psychiatric disorders, and a parental diagnosis of OCD was second only to a parental diagnosis of schizophrenia in regard to someone’s risk,” said lead author Sandra Meier, Ph.D., of the National Centre for Register-Based Research at Aarhus University.

“Does this mean that a parent of a child with OCD or someone with a parent with OCD should start worrying about schizophrenia? The answer to that is no,” said Helen Blair Simpson, M.D., Ph.D., director of the Anxiety Disorders Clinic at Columbia University. “The context of data is always important, and in this case less than 3 percent of all people with a schizophrenia disorder also had OCD.”

Simpson also told Psychiatric News that this study had a diagnostic limitation in that cases of mild OCD are typically treated by general clinicians in Denmark. While this study included only patients with a psychiatric hospital contact, the results may not be applicable to all OCD cases.

“However, the study does raise some interesting questions regarding the trajectory of mental illness,” Simpson said. “I think we see a lot of mental comorbidities in psychiatric disorders because at the level of the brain, many neural substrates are shared among different disorders. But what is diagnosed as two conditions may be a more nuanced story wherein one disorder develops symptoms that overlap with another condition.”

Using this Danish study as an example, Simpson suggested that some of the observed associations could be due to an initial misdiagnosis of OCD in these patients who were in a prodromal stage of schizophrenia in which obsessive symptoms manifested first.

Meier echoed the thought that the phenotypes of OCD and schizophrenia are likely more similar than currently appreciated and that clinicians should be more aware of the link between these two illnesses.

“Even if the association we found is not causal—and instead an epiphenomenon due to genetics or environmental factors—treating the comorbid OCD may prevent and improve the symptoms of schizophrenia, and the patients still benefit,” Meier said.

This study was supported by the Lundbeck Foundation Initiative for Integrative Psychiatric Research. ■