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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.

     

    Duchenne muscular dystrophy

    Duchenne MD is a sex-linked disorder, and two-thirds of the cases are genetic. The disorder has very specific diagnostic signs. The CPK can be extremely high, sometimes in the many thousands. Boys are generally late walkers and even small boys show beginning proximal weakness, tightness of the heel cords, and difficulty getting up from the floor (Gower sign). As the disease progresses, the heel cord tightness causes the boys to walk on their toes.

    Stretching of contractures and heel cord lengthening done at the proper time can greatly improve boys’ ability to get around. Contractures develop in a very specific pattern. Two-thirds of the patients show some developmental delay and learning disabilities. Calf enlargement also may be present.

    Prednisone treatment is still advocated by Victor Dubowitz, MD, Professor Emeritus of the Royal College of Paediatrics and Child Health, London, United Kingdom (personal communication, 2016). He is a pediatric neuromuscular specialist and founder of the World Muscle Society. Now new drugs are also being tried.

    The muscle biopsy is very specific. Scoliosis and cardiac and pulmonary problems develop as the boys age. Keeping them ambulatory and watching for increased weight gain and blood pressure are extremely important.

    Becker muscular dystrophy

    Becker MD is another sex-linked recessive disorder. It is much more benign than Duchenne MD and usually has a later onset. The CPK can be markedly elevated. Boys may develop mild muscle weakness and can have difficulty being as active as friends their own age. Walking can be possible until the early 30s. Mild contractures may develop and the calves may be enlarged. Cardiac problems are important to watch for, and the mothers who are carriers may also develop cardiac difficulties.

    Malignant hyperthermia (MH) is associated with MD.7 Patients with both Duchenne MD and central core disease are at risk. The gene for this disorder, 19q, and the gene for central core disease are the same, so these patients are at particular risk. Malignant hyperthermia can cause severe problems during a surgery and even death if the anesthesiologist is not prepared to treat the problems that can develop.

    When a child has muscle weakness, it is important to ask if a relative has ever had problems with an anesthetic. The drug sevoflurane and its related agents should not be used. Also, the anesthetic machine should be flushed out prior to any surgery on a patient with muscle weakness. If a child manifests this disorder, other family members should be alerted as they, too, may be at risk. There is an MH hotline with an anesthesiologist always available to answer calls: 1-800-644-4917.

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     A complete neuromuscular workup must be done before any diagnosis of a muscle disorder is made (Table 2). A neuromuscular workup includes the patient’s history; a family history of muscle weakness or anesthetic problems; and a complete physical examination with the patient undressed down to his/her shorts or underpants. A muscle biopsy is performed using a local anesthetic because of the risk of MH. A CPK lab test, and genetic tests if indicated, complete the workup. Until all these are done, no diagnosis of a muscle disease should ever be made.

    Experts say a muscle biopsy can guide a physician to order the appropriate gene studies. I am told by Caroline Sewry, professor of Muscle Pathology at Dubowitz Neuromuscular Centre, London, England, that gene studies do not always pick up deletions and duplications (personal communication, 2017).

    If the diagnosis of a muscle disorder is confirmed, communication with the parents should always be done face-to-face, not over the telephone. Parents hear the words ”muscular dystrophy” and their world topples.

    In summary

    Making the diagnosis of Duchenne or Becker MD on the basis of a single elevated CPK can be a tragic error resulting in fear and pain for the parents. The 8 cases I presented here show the fallibility of doing this. Myositis in different forms can have markedly elevated CPKs, but the CPK can be normal in about 25% of cases. Early treatment with prednisone and sometimes additional drugs can completely reverse the muscle weakness.

    Emery-Dreifuss MD patients can have a moderate elevation of CPK. This diagnosis is important to make because the insertion of a pacemaker for arrhythmia can be lifesaving. Limb-girdle MD patients may have a moderately elevated CPK and a much longer life span than Duchenne patients.

    The importance of a complete workup for a muscle disease is imperative before parents can be given a specific diagnosis.

    REFERENCES

    1. Cuestas RA Jr. Creatine kinase isoenzymes in high-risk infants. Pediatr Res. 1980;14(8):935-938.

    2. Thompson CE. Infantile myositis. Dev Med Child Neurol. 1982;24(3):307-313.

    3. Walton JN, Adams RD. Polymyositis. Baltimore: Williams and Wilkins; 1958.

    4. Goebel H, Sewry C, Weller R. Muscle Disease: Pathology and Genetics. 2nd ed. New Jersey: Wiley-Blackwell; 2013.

    5. Wang L, Liu L, Hao H, et al. Myopathy with anti-signal recognition particle antibodies: clinical and histopathological features in Chinese patients. Neuromuscul Disord. 2014;24(4):335-341.

    6. Emery AE, Dreifuss FE. Unusual type of benign X-linked muscular dystrophy. J Neurol Neurosurg Psychiatry. 1966;29(4):338-342.

    7. Thompson C. Raising a Child with a Neuromuscular Disorder. New York: Oxford University Press; 1999.


    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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