Chronic Fatigue Syndrome

Chronic fatigue syndrome (CFS) is a heterogeneous disease that presents with pronounced disabling fatigue, sleep disturbances, and cognitive impartment that negatively affect patients’ functional capability. CFS remains a poorly defined entity with an ill-defined etiological background. CFS is neither a novel diagnosis nor a new medical condition. From as early as the eighteenth century, a constellation of perplexing array of symptoms were observed that had descriptions resembling accompanying symptoms of chronic fatigue syndrome. During each time lapse, a certain concept was popularized. Commencing with febricula and ending with CFS, several terms were proposed including neurocirculatory asthenia, atypical poliomyelitis, Royal Free disease, effort syndrome, Akureyri disease, Tapanui disease, chronic Epstein-Barr virus syndrome, and myalgic encephalitis, among others. Moving to the modern era, it remains unclear whether CFS has an autoimmune component or is it a condition that precedes a full-blown autoimmune. Due to the various clinical presentations, accumulated evidence highlights the overlap with other conditions including postural orthostatic tachycardia (POTS), autoimmune syndrome induced by adjuvants (ASIA), and Sjögren’s syndrome, among others. It is postulated that an autoimmune disease would manifest early with ill-defined symptoms (e.g. typical of CFS), which when exposed to a secondary stimulus (e.g. antigen) might cause an acceleration of the natural course of the disease and, hence, a full-blown autoimmune disease. In this chapter, a historical background review of this disease and appraisal of our current rational regarding CFS are provided.