Has anyone heard of a disorder that causes exercise intolerance and post-exertional myalgia without any further symptoms (like generalised fatigue or joint pain)?
Detailed investigation showed that the patient's autoimmune screen and routine bloodwork is normal. No neurological abnormalities were found.
The symptoms include cramp-like muscle pain (without muscle rigidity), muscle tightness, and burning. The symptoms can be triggered within minutes of moderate activity (such as walking at a brisk pace) and involve predominantly the calves, thighs, forearms, biceps, and abdominal muscles. Only the exercised muscles show symptoms and these seem proportional to the power generated by the muscle. Lower intensity exertion is much better tolerated.
Resting for 5 - 10 minutes provides relief but continued exertion is followed by a worsening of the myalgia characterised by muscle pain at rest and muscle tightness that prevents the patient from stretching the muscle. During an episode of myalgia, the patient has difficulty climbing stairs and performing routine activities like grocery shopping.
An episode of post-exertional myalgia lasts approximately 10 - 14 days and eventually resolves while the patient avoids further exercise. CK levels were regularly monitored and remained within normal levels even during an episode of myalgia.