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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.

     

    A girl was born at term after a normal pregnancy and delivery. At age 6 months, she was noted to have an elevated CPK of 2500 U/L and some mild hypotonia. A neurologist reported an electromyogram (EMG) to be myopathic. The muscle biopsy was signed out as congenital MD. On examination, I found the child to be extremely bright with just mild muscle weakness. A review of the muscle biopsy slides revealed none of the distinctive changes of congenital muscular dystrophy.

    I had the original block recut and stained. Three of the 11 sections showed a striking perivascular inflammatory response. After a 2-week course of prednisone (1 mg/kg), the patient showed increased muscle strength and tone. After 3 months, the CPK was within normal limits. The child continued to improve and soon was able to take a few steps in long-leg braces. I have a long-term follow-up of the child. Although she has needed intermittent steroids, she has done well.

    Polymyositis

    Polymyositis is too often diagnosed as Duchenne MD. This is a treatable condition with excellent results when the diagnosis is made and prednisone treatment started in the early phases.

    Recommended: 7 lower limb positional variations

    Doctors John Walton (Lord Walton) and Raymond Adams wrote the definitive text about polymyositis in 1958.3 I was fortunate to spend time in Dr. Walton’s neuromuscular unit at the University of Newcastle located in Newcastle upon Tyne, United Kingdom, when he was dean of the medical school there. His teaching has allowed me to diagnose many cases of this disorder. It is exciting to watch patients respond to treatment once steroids are started. Initially, steroids should be given in a large dose (1 mg/kg-2 mg/kg) and then tapered off as the CPK lowers and the patient’s muscle strength improves.

    Dermatomyositis

    Another form of myositis is dermatomyositis (Figure 1).4 When these patients are seen by orthopedists or neurologists, they are frequently diagnosed as having some type of MD. If a pediatrician has a patient with muscle weakness and any kind of a skin rash, I would want the child or teenager to be immediately referred to a rheumatologist or a neuromuscular specialist who treats dermatomyositis.

    A 16-year-old girl complained of increasing muscle weakness. On examination, I found her to have mild proximal weakness, skin lesions typical of dermatomyositis, and a CPK of 1552 U/L. A muscle biopsy was done using a local anesthetic. The slides revealed typical inflammatory cells and other features of myositis. A daily initial dose of 60 mg of prednisone brought remarkable results. She slowly improved allowing the prednisone to be reduced. Her recovery was complete after many months of treatment. She later married and now dances with her husband’s band (Figure 2).

    A 5-year-old boy saw an orthopedic surgeon because of mild muscle weakness. The physician, on the basis of an elevated CPK and Gower sign (indicating hip girdle weakness), told the parents their son had Duchenne MD. When I saw the child for a neuromuscular workup, he had skin lesions typical of dermatomyositis. A muscle biopsy was performed using a local anesthetic and showed multiple inflammatory cells. The boy responded remarkably well to prednisone and we kept in touch for many years. He became a music instructor at a university.

    NEXT: Emery-Dreifuss muscular dystrophy

    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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