The cardinal symptom of ME in the historical literature was profound, post-exertional loss of muscle power associated with muscle pain, tenderness and swelling. The 2007 NICE Clinical Guideline requires “post-exertional” symptoms (delayed with slow recovery over several days) for a diagnosis. Some researchers have therefore focussed on patients’ responses to exercise in a laboratory setting as a means of understanding the illness and improving diagnosis.
One of these research groups, at the University of Utah, has been investigating the role of molecular receptors in muscle pain and fatigue, and their most recent report describes their efforts to determine differences in activity in the genes of ME/CFS and fibromyalgia patients before and after moderate exercise. The study included 48 patients with ME/CFS and fibromyalgia, 18 patients with fibromyalgia alone, and 49 healthy controls, and the genes examined were involved in signalling and modulating sensory fatigue and muscle pain. All participants underwent moderate exercise (one 25-minute session on a combined arm-leg cycle ergometer) and had blood samples taken.
In the healthy people and patients with fibromyalgia alone, there were no gene expression changes following exercise. However, in 71% of ME/CFS patients, moderate exercise increased the activity of most sensory and adrenergic receptor genes and one cytokine gene for 48 hours. These post-exercise increases correlated with measurements of fatigue and pain. In the remaining patients (who were more likely to have a history of orthostatic intolerance), genes were not altered apart from adrenergic a-2A receptor transcription, which was decreased at all time-points after exercise.
The fact that even moderate exercise led to increased expression of certain sensory ion channel, adrenergic and immune genes in a majority of ME/CFS patients brings an exercise-related “biomarker” for the illness closer. As the authors say, the post-exercise expression of four specific genes identified in their study meets published criteria (accuracy 0.80) for a “very good to excellent diagnostic tool”.
Reference: Gene expression alterations at baseline and following moderate exercise in patients with Chronic Fatigue Syndrome and Fibromyalgia Syndrome. Light AR et al. J Intern Med 2012 Jan; 271(1): 64-81.