Fluctuating illness

A fluctuating illness is one in which either symptoms or the course of the illness varies in severity or impact over time. Symptoms in a fluctuating illness may "wax and wane" within a period of time, whether the course of the illness has a relapsing-remitting pattern or not. Many chronic illnesses are fluctuating illnesses, in which a person's level of disability varies.

ME/CFS
The CDC describes ME/CFS as a fluctuating illness, with post-exertional malaise (PEM) causing patients to disabling have "crashes" or "relapses" after exertion. Doctors, nurses and other healthcare providers are warned that: "'The severity and frequency of the symptoms can vary among patients and can vary for an individual patient. Symptoms can fluctuate during the day, from day to day, and throughout the illness. Some patients may not be obviously ill-appearing during clinical evaluations. However, if patients are severely affected or are having an exacerbation of their symptoms, even visiting a clinic for care might not be feasible at times. Thus, healthcare providers may not see patients when their symptoms are most severe.'"

Fluctuating symptoms
ME/CFS is frequently described as a fluctuating illness,, or as a serious illness with symptoms that can fluctuate in severity and hierachy from day to day or even from hour to hour.

Fluctuating illness course
Chu et al. (2019) investigated prognosis in ME/CFS patients are found that patients generally had one of several courses of illness:
 * 4% constantly improving
 * 8% persisting/little change in symptoms
 * 7% relapsing-remitting (all symptoms might disappear for a time only to return)
 * 59% fluctuating (symptoms always present)
 * 14% constantly worsening
 * 7% other pattern

Remissions
Chu's study found that 13% of the ME/CFS patients had experienced one or more remission (i.e., period of time with no symptoms) lasting a month. The average remission lasted 7 months and the longest was 2 years.

Diagnostic criteria
In the London criteria for myalgic encephalomyelitis, fluctating symptoms are one of the five compulsory disagnostic criteria]: "'Fluctuation of symptoms, from hour to hour and day to day'" The International Consensus Criteria states: "'There may be marked fluctuation of symptom severity and hierarchy from day to day or hour to hour. Consider activity, context and interactive effects.'"

The ICC also states that in ME "prominent symptoms tend to vary rapidly and dramatically."

Severe ME
A small study of severe ME/CFS described symptoms as fluctuating and unpredictable, with severe and very severe ME having severe symptoms ever day, and only some patient having very brief moments in which they could do "normal activities": "'At best, energy fluctuations allow individuals to experience only fleeting moments of 'normal'. For example, Jane stated she was active for 2% of the day when she washed and toileted, whereas Lorraine was completely bedbound and dependent on assistance just to sit up in bed.'"

Possible causes of fluctations
Tate et al. (2018) states fluctuations in ME/CFS symptoms may result from neuroinflammation: "'Inflammatory marker' studies, including magnetic resonance imaging (MRI) pre- and post-exercise studies, support the concept that symptom severities likely 'wax and wane' in tandem with fluctuating levels of chronic neuroinflammation in the brains and CNS of ME/CFS patients, and this is an important feature of this paradigm."

People with ME/CFS generally have a blunted rise in heart rate as activity increases in intensity during (as shown during cardiopulmonary exercise testing), which worsens with post-exertional malaise. This suggests cardiac autonomic dysregulation, which may cause fluctuating symptoms.

A "boom and bust" cycle of overactivity (on better days) then less far activity (due to crashing caused by post-exertional malaise) also leads to large fluctuations in symptoms. Activity pacing is often suggested to address this.

Notable articles
We Already Know Enough to Avoid Making the Same Mistakes Again With Long COVID - (Blog, Full text)
 * 2021, Exploring Symptom Fluctuations and Triggers in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Using Novel Patient-Centred N-of-1 Observational Designs: A Protocol for a Feasibility and Acceptability Study -  (Abstract)
 * "This study will assess the feasibility and acceptability of patient-centred N-of-1 observational studies to assess diseases with complex presentations such as ME/CFS, as well as provide individual-level evidence about fluctuations and triggers of ME/CFS symptoms that may aid self-management."


 * 2019, Onset patterns and course of myalgic encephalomyelitis/chronic fatigue syndrome (Full text)
 * 2018, Adolescent's descriptions of fatigue, fluctuation and payback in chronic fatigue syndrome/myalgic encephalopathy (CFS/ME): interviews with adolescents and parents - (Full text)
 * 2011, Symptom fluctuations and daily physical activity in patients with chronic fatigue syndrome: a case-control study - (Full text)

Learn more

 * Presentation and Clinical Course of ME/CFS - CDC