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

 * 84.3% - 88.3% of the 2073 patients in a Belgian study of 2001 reported muscle weakness.
 * Katrina Berne 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. An attempt has not been made to reproduce this finding in published research.

Newton, lactate dehydrogenase

Learn more

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