How ME/CFS Research Can Provide New Insights Into Long COVID

On Monday, September 19, 2022, #MeAction Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and long COVID activists protested to address the crisis in the country with post-viral diseases. For the past four decades, considerable work in laboratories around the world had occurred with ME/CFS, and there are many lessons those battling the current pandemic can learn from their research.

Although some long COVID symptoms are unique, such as hair loss, the majority of symptoms experienced by those with ME/CFS and long COVID are comparable. Most patients with ME/CFS also had a viral infection at the onset. Given the similarities in these two illnesses, we might have an idea of the prognosis of those diagnosed with long COVID by inspecting what has occurred over time with ME/CFS. We do know that the percentage of adults and youth with severe symptoms of these various infections is initially high, and then tends to decrease over time. As an example, Hickie et al. (2006) launched a prospective study following adult patients from the time of acute infection with Epstein-Barr virus (glandular fever), Coxiella burnetii (Q fever), or Ross River virus (epidemic polyarthritis). The occurrence of post-infective fatigue syndrome decreased over time: 35% at six weeks, 27% at three months, 12% at six months, and 9% at 12 months. Decreases in ME/CFS have also occurred in pediatric samples, such as Katz et al.’s (2009) investigation of youth following Infectious Mononucleosis. We might therefore expect decreases in symptoms for those with long COVID, but among those who do not recover, it is important not to question the legitimacy of patients’ persisting symptoms, as this trauma has occurred far too often among those with ME/CFS.

In addition, there are lessons to be learned in how we gather data. As an example, in adult and pediatric community-based epidemiologic studies, from 90 to 95% of patients with ME/CFS do not know they have ME/CFS (Jason, Richman, et al., 1999; Jason, Katz, et al., 2020). Therefore, due to participants not knowing the symptoms of ME/CFS, it is not sufficient to just ask patients whether or not they have ME/CFS, as most have no idea of what symptoms are in the established ME/CFS case definitions. In addition, asking the participants whether they had been diagnosed with ME/CFS has problems in that many health care practitioners have difficulties making accurate diagnoses as they are not familiar with established ME/CFS case definitions. As has been learned by ME/CFS researchers, using psychometrically sound instruments with good reliability and validity is key to determining whether patients meet case definitions (Jason & Sunnquist, 2018).

How questions are asked is also worth examining. For many years, data in the ME/CFS field only assessed the occurrence of symptoms, but in the 1990s, it was apparent that the somatic symptoms in the ME/CFS criteria were very common in the general population (Jason, King, et al., 1999) and so occurrence measures were determined to be too imprecise. The field then moved to assess the frequency of symptoms in the ME/CFS case definitions. However, researchers encountered another conceptual problem as those patients with Major Depressive Disorder had a similarly high frequency of fatigue as patients with ME/CFS. In other words, one of the most prevalent mental health disorders (Major Depressive Disorder) could not be differentiated from ME/CFS using just measures of frequency. However, when measures of severity were introduced, those with ME/CFS had significantly higher levels of fatigue severity than patients with Major Depressive Disorder (King & Jason, 2005). So, by assessing frequency and severity, it was possible to make this important diagnostic differentiation between ME/CFS and psychiatric conditions.

Perhaps the most important symptom in measuring ME/CFS has been referred to as post-exertional malaise, as also indicated in the Jason et al. (2015) study above. This symptom is now being recognized by influential PASC investigators, such as in Choutka, Jansari, Hornig, and Iwasaki’s (2022): “Studies should include features such as post-exertional symptom exacerbation and other characteristic symptoms and signs to better capture the complex clinical picture seen in PAISs.” But this symptom is almost always asked in a binary fashion rather than how often it occurs and with what severity. There is also a need to determine what symptom frequency and severity scores make the best threshold for discriminating whether a person has an illness or not (Watson et al. (2014).

The issues above deal with criterion variance, sensitivity, and specificity, and they are of importance in considering how to best identify patients with ME/CFS in the current long COVID research. There are advantages to using instruments that have adequate psychometric properties, and that have been previously used with ME/CFS samples. Given the importance of determining which PASC patients meet these well-established criteria, a brief psychometric valid instrument should be used to assess critical ME/CFS symptoms and thus identify patients who meet ME/CFS case definitions (Sunnquist, Lazarus, & Jason, 2019).