Multiple Abnormalities Identified
There were no differences between the PI-ME/CFS and control groups in ventilatory function, muscle oxygenation, mechanical efficiency, resting energy expenditure, basal mitochondrial function of immune cells, muscle fiber composition, or body composition, suggesting the absence of a resting low-energy state, the authors said.
In 40-minute head-up tilt-table testing, there were no differences between the ME/CFS and control groups in frequency or orthostatic hypotension or extensive orthostatic tachycardia. However, a 24-hour ambulatory electrocardiogram showed that the patients with PI-ME/CFS had diminished heart rate variability. They also showed increased heart rate throughout the day, suggesting increased sympathetic activity, and a diminished drop in nighttime heart rate, suggesting decreased parasympathetic activity.
“Considered together, these data suggest that there is an alteration in autonomic tone, implying central nervous system regulatory change,” Dr. Walitt and colleagues wrote.
On the “Effort-Expenditure for Rewards Task,” the participants with PI-ME/CFS showed significant differences in “effort preference,” or a tendency to avoid the harder tasks, as well as a slowing of button-pushing over time, compared with the controls, even with easier tasks. This pattern suggests that those with PI-ME/CFS were “pacing to limit exertion and associated feelings of discomfort,” the authors wrote.
Dr. Nath describes this behavior as akin to “if you develop a flu, you feel that you just want to lay down in bed and not hurt yourself. It’s not that you’re not capable of doing [the task], but your body tells you don’t do it. Your body just wants to fight the infection ... these people just never bounce back.”
Compared with the controls, the participants with PI-ME/CFS failed to maintain a moderate grip force even though there was no difference in maximum grip strength or arm muscle mass. This performance difference correlated with decreased activity of the right temporal-parietal junction, a novel observation suggesting that the fatigue in the PI-ME/CFS group “is due to dysfunction of integrative brain regions that drive the motor cortex, the cause of which needs to be further explored,” Dr. Walitt and colleagues wrote.
On cardiopulmonary testing, peak power, peak respiratory rate, peak heart rate, and peak VO2 were all lower in the PI-ME/CFS group, correlating to a difference of approximately 3.3 metabolic equivalent of task units. The differential cardiorespiratory performance relates to “autonomic function, hypothalamic-pituitary-adrenal axis hyporesponsiveness, and muscular deconditioning from disuse that clinically impacts activities of daily life,” they said.
In the participants with PI-ME/CFS, catechol levels in cerebrospinal fluid correlated with grip strength and effort preference, and several metabolites of the dopamine pathway correlated with several cognitive symptoms.
“This suggests that central nervous system catechol pathways are dysregulated in PI-ME/CFS and may play a role in effort preference and cognitive complaints,” as well as decreased central catecholamine biosynthesis. Similar findings have been seen in patients with long COVID, the authors noted.
There were increased naive B cells and decreased switched memory B cells in blood of participants with PI-ME/CFS. Contrary to prior studies, there was no consistent pattern of autoimmunity across all participants with PI-ME/CFS, and no previously undescribed antibodies were identified.
However, programmed cell death protein 1, a marker of T-cell exhaustion and activation, was elevated in the cerebrospinal fluid of the patients with PI-ME/CFS.
Several sex-based differences were noted, including in immune cell expression in cerebrospinal fluid, peripheral blood mononuclear cell gene expression, and muscle gene expression. Males and females also differed in the cerebrospinal metabolomics that distinguished the participants with PI-ME/CFS from controls.