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RESEARCH WEEKLY: Examining the Interconnectedness of Schizophrenia and Inflammation

RESEARCH WEEKLY: Examining the Interconnectedness of Schizophrenia and Inflammation 
By Kelli South

The relationship between schizophrenia and inflammation in the body has been the subject of much research in recent decades. A growing body of evidence suggests that inflammation is associated with schizophrenia in a number of ways: from increasing the risk of developing schizophrenia to indicating treatment efficacy in those who already have schizophrenia.
Inflammation is the body’s natural response to infection, triggered by the immune system to fight unwanted pathogens in the body. Inflammation can also occur in situations where no infection is present, leading to chronic inflammation that can cause health problems.
A new article in Focus, an educational journal published by the American Psychiatric Association, synthesizes the research literature on schizophrenia and inflammation, categorizing the findings over the life course of schizophrenia, from pre-onset of the illness through the treatment phase. The authors highlight replicated findings that indicate associations between inflammation and schizophrenia and call for further research in every area.

Risk factors 

There are numerous studies examining genes that may play a role in developing schizophrenia, including several genes related to the immune system. Because there is a close relationship between the immune system and inflammation, it is possible that the presence of these genes in particular could be associated with a higher risk of developing schizophrenia, according to the research cited.
Other studies focus on the possibility that an infection of a pregnant mother with inflammation causing viruses, bacteria or parasites could lead to altered brain development in the fetus, leading to an increased risk of schizophrenia development later in life.
Additionally, the risk of inflammation for developing schizophrenia may continue after a child is born and through their adolescence; some studies found that hospitalization for autoimmune disorders or other inflammation causing infections during childhood or adolescence were associated with schizophrenia development later in life.

Impact on those already diagnosed with schizophrenia 

Adults with schizophrenia or certain other psychotic illnesses, as well as their first-degree family members, may have an increased prevalence of autoimmune diseases linked with inflammation. Relatedly, studies found that a family history of autoimmune disease was associated with increased risk of schizophrenia. This suggests a bidirectional relationship between inflammation-causing autoimmune diseases and schizophrenia, where it is unclear which factor is causing which.
One study that analyzed those experiencing their first episode of psychosis found elevated inflammation levels, suggesting some relationship between the two factors. The authors call for more research on the amount of inflammation present in patients with treatment-resistant psychosis.

Symptomology 

Research of increased inflammation in the general population have found effects on brain cognition. While some studies specifically examine the effect of inflammation on cognition in people with schizophrenia or psychosis, the small associations found in these studies are not definitive. The results could indicate that inflammation in people with schizophrenia might lead to worsened symptoms.
The authors also discuss the role that inflammation may play in the treatment of schizophrenia. Certain indicators of inflammation may also indicate whether a patient is responding to treatment for schizophrenia, which could predict symptom severity and illness outcomes for the future of the patient. Last, they discuss the possibility of anti-inflammatory drugs as a treatment for schizophrenia. While the evidence of the efficacy of NSAIDs or other anti-inflammatories is mixed, the authors view this as an exciting area for future research.

Implications 

It is important to note that the authors do not conclude any definitive causal relationships between inflammation and schizophrenia and they do not find enough evidence to say that schizophrenia is an inflammatory disorder. They point to the heterogeneity of schizophrenia as an illness and posit that inflammation may only be a major factor for a certain subset of people with schizophrenia.
To highlight this hypothesis, the authors point to the discovery of neurosyphilis in the 20th century as a cause of psychotic symptoms for a subset of people living in psychiatric hospitals. After the discovery of neurosyphilis as a cause and the invention of penicillin as a cure, treating this specific subset of patients with psychosis changed entirely. They believe that inflammation may follow a similar path, allowing patients whose schizophrenia is, or would be, affected by inflammation to reduce their risk for developing the illness, reduce symptom severity, and increase treatment options and effectiveness. Ideally, this change would eventually lead to a better quality of life for this group of people.
Treatment Advocacy Center founder Dr. E. Fuller Torrey helped pioneer the hypothesis of the relationship between schizophrenia and inflammation, paving the way for the work being done today. Much more research is needed on this topic; it could lead us closer to understanding the differences among those with schizophrenia and providing more effective prevention and treatment for the illness.

References 

Miller B and Goldsmith D. (November 2020). Evaluating the hypothesis that schizophrenia is an inflammatory disorder. Focus.
Kelli South is the research assistant at the Treatment Advocacy Center.