More than 70% of patients with autoimmune disease report experiencing mental fatigue or “brain fog.” It’s the primary reason for work disability in people with autoimmune disorders and has collectively been named the most difficult disease symptom to cope with. 

Autoimmune diseases occur when the body's immune system triggers an inflammatory response, but there is no foreign threat present. Pathogen-fighting cells attack the body’s own healthy cells and tissues. While in the midst of this inflammatory response, many autoimmune patients report feeling mentally fatigued; researchers and doctors have long wondered — why? 

Finding the connection

A recent study published in Neuroimage from the University of Birmingham, in collaboration with the University of Amsterdam, recently uncovered a connection between inflammation seen in autoimmune diseases and the accompanying brain fog. According to the study, inflammation affects the brain's ability to reach and maintain a state of alertness, leading to exhaustion.

Renowned neurologist and fatigue researcher Dr. Lauren Krupp defined chronic fatigue as “an overwhelming sense of tiredness, lack of energy and feeling of exhaustion.” Many people think of chronic tiredness when considering fatigue. However, mental fatigue does not respond to rest or sleep the way tiredness does.

During the study, researchers assessed three separate attention processes involving specific parts of the brain. The processes included alerting (reaching and maintaining an alert state), orienting (selecting and prioritizing useful sensory information) and executive control (used to direct attention and focus when available information is conflicting).

Twenty volunteers were injected with a salmonella typhoid vaccine to stimulate temporary inflammation. A few hours later, volunteers were shown simple images on a computer screen. While in an inflamed state, their brain activity and cognitive responses to the images were measured. Researchers examined the volunteers' ability to control attention and remain alert while in an inflamed state.

"These results show quite clearly that there's a very specific part of the brain network that's affected by inflammation," said Dr. Ali Mazaheri, senior author of the study. "This could explain 'brain fog'."

Looking to the future of treating autoimmune diseases

"Getting a better understanding of the relationships between inflammation and brain function will help us investigate other ways to treat some of these conditions,” said Dr. Leonie Balter, the first author of the study.

Further research might show that patients with conditions associated with chronic inflammation, such as obesity, kidney disease or Alzheimer's, could benefit from taking anti-inflammatory drugs to help preserve or improve cognitive function.

Subtle changes in brain function may be used as an early marker for cognitive deterioration in patients with inflammatory diseases, Balter concluded.