Postinfectious myalgic encephalomyelitis/chronic fatigue syndrome (PI-ME/CFS) is a distinct, centrally mediated condition, with evidence of autonomic, immune, and metabolic dysfunction, new "deep phenotyping" data suggested.
The study was initiated in 2016 at the US National Institutes of Health. Its aim was to better elucidate the underlying pathophysiology of ME/CFS, a multisystem disorder characterized by persistent and disabling fatigue, post-exertional malaise, cognitive complaints, and other physical symptoms. A total of 17 carefully selected individuals with PI-ME/CFS onset within the prior 5 years were compared with 21 healthy volunteers on a more extensive set of biologic measurements than has been examined in any prior study of the condition.
Overall, the findings suggested that ME/CFS is “a distinct entity characterized by somatic and cognitive complaints that are centrally mediated,” with fatigue that is “defined by effort preferences and central autonomic dysfunction,” Brian T. Walitt, MD, of the National Institute of Neurological Disorders and Stroke (NINDS), Bethesda, Maryland, and colleagues wrote in the paper, published on February 21 in Nature Communications.
In addition, “there are distinct sex signatures of immune and metabolic dysregulation which suggest persistent antigenic stimulation.” Physical deconditioning over time, while not the source of the condition, “is an important consequence,” the authors added.
Asked to comment, Hector Bonilla, MD, director of the ME/CFS Clinic and codirector of the Stanford Post-Acute COVID-19 Syndrome Clinic, Atherton, California, pointed out that the sample was small and the study was cross-sectional and therefore likely missed dynamic changes in the patients.
Nonetheless, Dr. Bonilla told this news organization, “they have shown clear objective changes in patients with ME/CFS not seen in the controls. These are present in the microbiome, in the immune system, and in metabolites, especially in spinal fluid, that lead to a neuroinflammatory condition. And these are linked with autonomic dysfunction that can explain many of the symptoms that patients experience ... The symptoms are not manufactured by them.”
Thus far, the only treatments for ME/CFS are symptomatic. Understanding the pathophysiology is essential to identifying disease-modifying therapy, study lead author Avindra Nath, MD, Senior Investigator and Clinical Director of Intramural Research at NINDS, told this news organization.
“The disease is real. But our medical profession is limited in what they can do to diagnose or impact them ... The first thing we need to do is try to understand the pathophysiology. So that’s why the study was put together,” Dr. Nath said.
Postinfectious syndromes including ME/CFS have been given many names, including post-Lyme disease, Gulf War illness, and more recently, long COVID. With ME/CFS, the Epstein-Barr virus has historically been one of the most commonly associated triggers, although several other viral, bacterial, and environmental toxins have been implicated.
“There are a whole host of these things that have very similar symptoms or overlapping symptoms ... It’s quite possible that the underlying pathophysiology overlaps between all these syndromes,” Dr. Nath noted.
Another ME/CFS expert not involved in the study, researcher Michael VanElzakker, PhD, of the Neurotherapeutics Division at Harvard Medical School and Massachusetts General Hospital, Boston, said that the possibility of antigen persistence of the infectious pathogen arising from the immune system profiling conducted in the study is noteworthy and merits further study.
“To me, the obvious next step would be techniques like tissue-based assays and T-cell sequencing to try and understand what exactly those antigens are and what their source might be. Importantly, it is probably not the same antigen or pathogen source in all patients, but that’s a question that needs an answer,” Dr. VanElzakker said.
Of note, the 17 study participants had been adjudicated by an expert panel from an initial 484 inquiries and 217 who underwent detailed case reviews. They had to meet at least one of three published ME/CFS criteria and to have moderate to severe clinical symptom severity as determined by several fatigue scores. None met the criteria for psychiatric diagnoses.
Yet, even in the cases that met study criteria, underlying causes emerged in 20% of the participants over time, suggesting diagnostic misattribution. “This misclassification bias has important ramifications on the interpretation of the existing ME/CFS research literature,” the authors wrote.
Dr. VanElzakker noted, “The fact that this research study was probably the most detailed workup many of these patients had ever gotten is a serious indictment of our current profit-based healthcare system’s prioritization of 15-minute doctor’s appointments. It is almost certain that other patients would also benefit from an intensive detailed workup.”