Their conclusions were based on previous studies that found many normal physical test results, a lack of a discernible cause, and a higher prevalence of the illness in females. Consequently, the authors recommended that the disease should be renamed "myalgia nervosa". This perspective was rejected in a series of case studies by Dr. Melvin Ramsay and other staff of the Royal Free Hospital, the center of a significant outbreak. The  psychological hypothesis posed by McEvedy and Beard created great controversy, and convinced a generation of health professionals in the UK that this could be a plausible explanation for the condition, resulting in neglect by many medical specialties. The specialty that did take a major interest in the illness was psychiatry.Because of the controversy, sociologists hypothesized that stresses of modern living might be a cause of the illness, while some in the media used the term "Yuppie flu" and called it a disease of the middle class. People with disabilities from CFS were often not believed and were accused of being malingerers. The November 1990 issue of Newsweek ran a cover story on CFS, which although supportive of an organic cause of the illness, also featured the term yuppie flu, reflecting the stereotype that CFS mainly affected yuppies. The implication was that CFS is a form of burnout. The term yuppie flu is considered offensive by both patients and clinicians.In 2009, the journal Science published a study that identified the XMRV retrovirus in a population of people with CFS.
The World Health Organization classes chronic fatigue syndrome as a central nervous system disease.Some neuroimaging studies have observed prefrontal and brainstem hypometabolism; however, sample size was limited. Neuroimaging studies in persons with CFS have identified changes in brain structure and correlations with various symptoms. Results were not consistent across the neuroimaging brain structure studies, and more research is needed to resolve the discrepancies found between the disparate studies.Tentative evidence suggests a relationship between autonomic nervous system dysfunction and diseases such as CFS, fibromyalgia, irritable bowel syndrome, and interstitial cystitis. However, it is unknown if this relationship is causative. Reviews of CFS literature have found autonomic abnormalities such as decreased sleep efficiency, increased sleep latency, decreased slow wave sleep, and abnormal heart rate response to tilt table tests, suggesting a role of the autonomic nervous system in CFS. However, these results were limited by inconsistency.Central sensitization, or increased sensitivity to sensory stimuli such as pain have been observed in CFS. Sensitivity to pain increases after exertion, which is opposite to the normal pattern. Immunological
Immunological abnormalities are frequently observed in those with CFS. Decreased NK cell activity is found more often in people with CFS and this correlates with severity of symptoms. People with CFS have an abnormal response to exercise, including increased production of complement products, increased oxidative stress combined with decreased antioxidant response, and increased Interleukin 10, and TLR4, some of which correlates with symptom severity.