Living with multiple sclerosis or any life-long disease is not easy. Although an increased rate of depression is not unexpected, the tendency for people with M.S. to have significantly higher rates of depression than others with similar conditions, has been baffling.
Symptoms of multiple sclerosis stem from abnormal responses of the body’s immune system.
New research now suggests that inflammation within the hippocampus — influenced by the immune system responses — may be the reason for the increased prevalence of depression among people with M.S.
The study, published in the journal Biological Psychiatry, supports this hypothesis, providing evidence that inflammation of the hippocampus alters its function and contributes to symptoms of depression.
“This study elegantly links hippocampal inflammation to depression,” said Dr. John Krystal, Editor of Biological Psychiatry. The research was a collaboration between King’s College London, Imperial College London, and Imanova Center for Imaging Sciences.
Led by senior authors Paul Matthews and Eugenii Rabiner, the research team designed a novel approach to investigate the link between brain immune responses and depression.
Researchers combined two complementary brain imaging techniques to study the relationship between hippocampal immune response, functional connections, and depressive symptoms.
The study was performed on 13 patients with multiple sclerosis and 22 healthy control subjects.
Positron emission tomography (PET) allowed for quantification of activated microglia, a measure of immune response. Functional magnetic resonance imaging (fMRI) assessed the strength of hippocampal connections to an extensive network of brain regions involved in emotion.
First author Dr. Alessandro Colasanti, of King’s College London, explained that PET imaging revealed immune activation in the hippocampus of patients with multiple sclerosis. “We also discovered that more inflammation was associated to more severe symptoms of depression,” said Colasanti.
Measurements of functional brain connections with fMRI during rest showed that immune activation in the hippocampus altered its connections with other brain regions.
“This study, combining two advanced complementary brain imaging methods, suggests that the inflammation of the hippocampus affects the brain function and causes depression,” said Colasanti.
As such, the findings suggest that hippocampal inflammation could be the contributing cause of high rates of depression in multiple sclerosis.
The new knowledge may be clinically significant as an effective and targeted treatment of brain inflammation could help to restore brain function and protect against depression among individuals with multiple sclerosis.