Muscle fatigability

Muscle fatigability in ME is a symptom in which muscles become weaker after minor exertion and a long period (3-5 days or longer) may elapse before full muscle power is restored. According to Melvin Ramsay, it is the defining feature of myalgic encephalomyelitis, without which a diagnosis of ME should not be made, though this symptom is noted to improve during remission. Similar muscle effects are known to occur in other neurological diseases such as multiple sclerosis and post-polio syndrome.

Prevalence

 * In a 2001 Belgian study, 84.3% of patients meeting the Fukuda criteria and 88.3% of patients meeting the Holmes criteria, in a cohort of 2073 CFS patients, reported muscle weakness.


 * Katrina Berne, PhD, reports a prevalence of 85-95% for muscle weakness.

Symptom recognition

 * In the Holmes criteria, unexplained generalized muscle weakness is an optional criteria for diagnosis, under the section Minor Symptom Criteria.

Possible causes

 * Muscle biopsies have shown evidence of mitochondrial degeneration, deletions of mitochondrial DNA, and the reduction of mitochondrial activity.


 * In addition, evidence of oxidative damage to muscles has been found in CFS.


 * Studies have found reduced levels of serum carnitine which return to normal after recovery and correlate with symptom severity.


 * Exercise has also been found to induce both early and excessive lactic acid formation in the muscles with a reduced intraceullar concentrations of ATP and acceleration of glycolysis.


 * Neurologist Peter Behan noted that ME patients were found to lack an important muscle enzyme called myoadenylate deaminase. A small peer-reviewed study found this present in only 5.5% of patients, and associated primarily with muscle pain rather than fatigue. Myoadenylate deaminase has since been ruled out as the sole cause of ME/CFS.

Learn more

 * 2016, Two Newcastle studies into muscle dysfunction and immune responses | read the lay summaries