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Infections may increase autoimmune disease risk in schizophrenia

Infections may play a role in the increased risk for autoimmune disease among patients with schizophrenia or a family history of the disease, according to research published in the American Journal of Psychiatry.

Michael E. Benros, MD, PhD, of the National Center for Register-based Research, Aarhus University, and the Mental Health Center Copenhagen, Copenhagen University Hospital, and colleagues said, "Infections may act as a common pathological mechanism for both psychosis and autoimmune diseases, or persons with psychosis may simply be more susceptible to acquiring infections than the general population, increasing the risk of autoimmune diseases."

Benros and colleagues identified 39,364 people with schizophrenia-like psychosis and 142,328 with autoimmune disease from a Danish cohort of 3.83 million. Their objective was to determine the risk for autoimmune disease among those with a schizophrenia or related psychosis diagnosis and whether infections influenced this risk.

Of those diagnosed with schizophrenia, 1,401 had a subsequent autoimmune disease; of these, 793 had a hospital contact for infection prior to their autoimmune disease diagnosis.

Among those with schizophrenia, the risk for one or more autoimmune diseases was increased by 53% (incidence rate ratio [IRR]=1.53; 95% CI, 1.46-1.62). Those with schizophrenia who had no hospital contact for infections had a slightly smaller risk for autoimmune diseases (IRR=1.32; 95% CI, 1.22-1.43). However, those with schizophrenia and a hospital contact for infection had a combined risk for autoimmune disease of 2.7 (95% CI, 2.51-2.89).

"The study shows that 3.6% of those with schizophrenia developed autoimmune diseases after the diagnosis and a previous study from the same group showed that 2.4% developed autoimmune diseases before the diagnosis with schizophrenia during the follow-up periods," Benros told Healio.com/Psychiatry.

A family history of schizophrenia slightly increased the overall risk for autoimmune disease among those with a family history of schizophrenia was slightly higher (IRR=1.06; 95% CI, 1.02-1.09) and 3.1% of those with autoimmune diseases had a family history of schizophrenia, according to the study.

"The increased risk of subsequent autoimmune diseases in individuals with schizophrenia may involve neuropsychiatric manifestations from the undiagnosed autoimmune disease, medical treatment or lifestyle associated with schizophrenia, or common etiological mechanisms, such as infections and shared genetic factors," they wrote.

Disclosure: The researchers report no relevant financial disclosures.