- Episodic Elevated CK with Reported Muscle Dysfunction: Episodes of elevated CK levels over the last 6 months -1 year (defined as ≥ 2X upper limit of age/gender-matched normal, or ≥ 500 units/L if age-matched reference is not established) not associated with an acute rhabdomyolysis event, AND patient report of frequent muscle fatigue, exercise intolerance, or limitation of exercise,