Ask anyone who suffers from an autoimmune disease or fibromyalgia about the most challenging aspect of their condition, and the answer will be unanimous--fatigue. The American Autoimmune Related Diseases Association (AARDA) conducted a survey, which found that "98 percent of respondents reported suffering from fatigue and 89 percent said that fatigue is a major issue for them." Fatigue is not the feeling one gets after working a 12-hour shift or running a half-marathon; it is an incapacitating, disabling exhaustion that is perpetually present and is not relieved by rest or a good night's sleep. It leads to poor quality of life, the inability to hold down a job, reduction in income, and stress on every relationship, both personal and professional.
Although chronic fatigue is common in many different diseases, it is poorly understood and not accepted as a debilitating problem by those who have not experienced it. In the survey by AARDA, "90 percent of the respondents said that they had discussed the intense fatigue with their families and friends, only 23 percent said that their families and friends understood while 49 percent said that they did not take the fatigue seriously." Fatigue and pain are subjective symptoms, meaning that neither is readily discernible by just looking at the person. Hence, the term 'invisible illness.'
Louati and Berenbaum conducted a literature review concerning the possible link of fatigue with depression, pain, and inflammation. They analyzed the physiological mechanisms that may explain the relationships between these factors, Their definition of fatigue that they based this study on was "a state of exhaustion and decreased strength accompanied by a feeling of weariness, sleepiness, and irritability, with a cognitive component." They found that there are multiple mechanisms involved in fatigue among different autoimmune diseases. Pain and fatigue are frequently seen together in both acute and chronic inflammatory diseases including rheumatic diseases, infection, cancer, and chronic fatigue syndrome. Decreasing inflammation may improve pain and fatigue levels. An interesting factor that the authors mentioned is that depression is often seen in fatigue, pain, and inflammatory diseases, but they don't elaborate.
Morris et al. touch on the relationship between depression and fatigue in their 2015 study. They note that 100% of people diagnosed with depression experience some level of fatigue, and research has shown that antidepressants do not affect fatigue. They discuss evidence that elevation of toll-like receptors (TLR), which are found on macrophages and dendritic cells, specifically TLR4, has been observed in suicidal patients. Chronic inflammation is known to be a significant player in the etiology of depression.
It's readily apparent that fatigue is a complex, multidimensional aspect of many chronic diseases that are still not well-understood. Since there appear to be many mechanisms of action that may be involved in the expression of fatigue in an individual, future research that identifies the different phenotypes of fatigue may lead to a better understanding of how to target its source and develop effective treatments to combat its debilitating effects. There also needs to be educational opportunities directed at those who are caregivers/supporters including family and friends in order to encourage empathy and compassion for those experiencing poor quality of life issues.