People with ME often experience a variety of additional illnesses or symptoms (comorbidities), such as fibromyalgia (widespread muscle pain), postural orthostatic tachycardia syndrome (POTS, rapid heart rate upon standing), and irritable bowel syndrome (bloating, constipation, and diarrhea). These diseases can also have their own distinct symptoms. It is important for the doctor to recognize and treat these comorbidities as they affect ME.
It is not easy for a patient to explain how she feels or why she does what she does, especially when those feelings and reasons are invisible. But it is important to share the story of ME so that others will understand the complexity and severity of this illness. The more the public understands ME, the more they will be able to support and help fund research that can lead to effective treatments.
ME is a specific neuromuscular disease that was described in the medical literature until 1988, when it was renamed chronic fatigue syndrome (CFS). The name change was made to avoid confusion with other illnesses that could be called fatigue, such as fibromyalgia and rheumatoid arthritis. CFS pushed ME into the background, but ME is still a real disease with distinctive features that cannot be dismissed. ME can be a life-threatening condition if left untreated.
The earliest description of ME involved its chronic, fluctuating nature and the presence of a single symptom known as post-exertional malaise (PEM). PEM is characterized by a worsening of symptoms following physical or mental exertion that would not have caused a problem before the illness, and it can last days or even permanently.
A diagnosis of ME requires at least one symptom from each of four different criteria systems: ME-ICC [30], the London criteria [32], the Canadian criteria for ME, and the International Association for CFS/ME diagnostic guidelines. The ME-ICC definition deviates from the original ME definition in several ways, including making muscle fatigability/long-lasting post-exertional muscle weakness optional rather than mandatory, and requiring that patients have “variable involvement of cardiac and other systems.”
To develop effective therapies for ME it is essential to investigate ME-specific patients, so a discriminative clinical definition of ME is necessary. This article presents a tentative definition for ME that includes the most important, distinguishing characteristics of the disease. This definition is based on the last two formal definitions of ME and on the symptoms observed in both epidemic and endemic cases of ME. It contains four mandatory elements: (1) muscle fatigability/long-lasting exercise-induced weakness; (2) the onset of symptoms during or after an episode of acute viral infection or exposure to noxious environmental factors; (3) a prolonged, relapsing course; and (4) evidence of neurological disturbance, particularly cognitive, autonomic, and sensory dysfunction. Prospective studies should investigate the overlap and differences between ME, CFS/ME, ME-ICC, and SEID in order to clarify which symptoms are mandatory for these four different systems of diagnosis. These studies should also investigate which symptoms are common to all these diagnoses. A more detailed, standardized definition of ME is needed for future use in medical practice and research.