An elevated CPK lab test may occur in active children, joggers, and other conditions. No diagnosis of muscular dystrophy should ever be made because of a single increased CPK. A complete work-up should be done if there is a question of muscle weakness. This includes a muscle biopsy using a local anesthetic.
Medicine has changed so much in the last years that many doctors order lab and genetic tests before or in place of doing a complete history and physical examination. When a CPK test is ordered and found to be elevated, doctors often rush to make the diagnosis of a muscle disease. If they tell a patient or parents they suspect muscular dystrophy or another muscle disease, the parents or adults will go through some terrible days. What the doctors do not know apparently is that a CPK test can be elevated in a very active child, in joggers, and sometimes in other circumstances. No diagnosis should ever be made on the basis of a single lab or genetic test. Lab errors also occur and any abnormal test should be repeated, preferably in another lab. Muscle biopsies are still indicated in a suspected muscle disease and these should always be done under a local anesthetic. If the patient has a muscle disease, such as central core, he or she is at risk for Malignant Hyperthermia if certain anesthetic agents are used for a biopsy done with a general anesthetic. This can cause tightening of the jaw and other symptoms which can cause death if not quickly treated.
All patients and parents should insist on a complete physical examination and history being done and a second opinion is always important if there is any doubt about a diagnosis.
The reverse of this is that a CPK can be normal in 25% of cases of polymyositis and dermatomyositis. Because knowledge of muscle diseases is something doctors in general seem to know little about, any diagnosis should be questioned until an expert in these disorders confirms it.