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    Elevated CPK: No short cut to muscular dystrophy diagnosis

    A pediatrician with special training in neuromuscular disorders cautions that nothing replaces the traditional workup—a complete history and physical—for diagnosing neuromuscular complaints.

    As medicine becomes more and more complicated, doctors are taking shortcuts that can profoundly hurt their patients. Taking histories, doing a complete physical examination, and talking with patients remain essential to good patient care. Instead, some doctors rush to order a battery of laboratory or genetic tests to replace a traditional workup.

    Using an elevated creatine phosphokinase (CPK) as a standalone test for the diagnosis of muscular dystrophy (MD) can be a serious error and could have devastating consequences for patients. Ordering lab work may save time, but it is important for physicians to recognize the fallibility of the tests. Accurate interpretation of the studies requires the knowledge obtained from a complete history and physical (Table 1).

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    Two girls, ages 3 and 4 years, were seen in emergency departments (EDs) by doctors in different states with the complaint of “stomach ache.” Lab work was ordered, and both children showed markedly elevated CPKs. The mothers were told their daughters probably had Duchenne or Becker MD. The mothers consulted me. After reviewing the children’s medical records, I referred them to neuromuscular specialists. Both children were later found not to have the disease. A complete history and physical would have given the ED physicians the information they needed to avoid such a dire misdiagnosis. The parents suffered unnecessary fear for their daughters’ health and life. Both children were without any family history of MD and without the physical signs of the disease. The misdiagnosis was based solely on the elevated CPKs.

    Possible reasons for elevated CPK

    There are many possible explanations for an elevated CPK that must be considered prior to giving a child the death sentence of the diagnosis of Duchenne MD. First among these is a marked elevation that can be seen when blood is drawn from an active screaming child. (Elevated CPKs can also be seen in infants born after a high-risk delivery.1) They soon return to normal values. Other disorders associated with high CPKs are myositis and some types of myopathy. These conditions can have good outcomes if treatment is started early.

    Myositis

    Myositis can occur in several different forms. Viral myositis with weakness and an elevated CPK may develop after a respiratory infection and especially during a flu epidemic. The children develop mild muscle weakness and pain in their lower extremities that can keep them from wanting to walk. The symptoms improve after a few days. No treatment is required other than bed rest and careful monitoring.

    Infantile myositis is frequently misdiagnosed as congenital MD.2 Only a few cases of infantile myositis have been reported in the literature.

    NEXT: More MD cases

    Charlotte E Thompson, MD, FAAP
    Dr Thompson is assistant clinical professor of Pediatrics, University of California San Diego School of Medicine, and the author of ...

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