Regularity in the change of serum creatine kinase level in Duchenne muscular dystrophy. A study with long-term follow-up cases.

Changes in the serum creatine kinase (CK) level according to the disease course were regressed to an exponential function Y = A e-ex in each case of 28 Duchenne muscular dystrophy (DMD) through a long-term follow-up study. The regression to this formula implies that DMD muscle would decay by the leaking of a certain amount of CK into the circulation in proportion to the existing muscle. The diminution coefficient "r" was significantly reduced in puberty as compared with ages around ten. The cases of rapid progression showed a high rate of CK decrement in puberty. The diminution rate of CK is suspected to reflect the difference between the rate of muscle growth and primary muscle decay.