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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 neurologist in a university medical school saw a 4-year-old girl because of her slowly increasing proximal muscle weakness. She also showed weakness of the neck muscles. Her parents reported weight loss and difficulty swallowing. A CPK of 4700 U/L was reported. A muscle biopsy showed a myopathy with no specific diagnosis. The neurologist told the parents the diagnosis was most likely MD because of the elevated CPK.

    The parents did some research and remembered that their daughter had had a rash several months before. They had been referred to a dermatologist and cortisone was prescribed with some improvement of the rash. The mother brought her daughter to see me, and on examining the child, I found diffuse proximal weakness of the pelvic and shoulder muscles. She also had a positive Gower sign upon trying to get up from the floor and marked neck weakness. I did not see any rash at that time.

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    On reviewing the muscle biopsy, I saw diffuse inflammation and some areas of focal inflammation. There were also some nonspecific changes. I diagnosed dermatomyositis and started the child on prednisone 1 mg/kg. The family returned to their home and I worked with their pediatrician to be sure the child received an adequate dose of prednisone. The mother and I kept in contact by telephone and e-mail. The little girl did well. Two years ago, I received a lengthy e-mail bringing me up to date. The mother said the girl was now a healthy 20-year-old.

    Signal recognition particle myopathy

    Signal recognition particle (SRP) myopathy is a fairly newly described disorder that mimics polymyositis.5 It can also be mistaken for MD.

    A teenager who excelled in sports began to lose muscle strength, so his parents consulted a neurologist at a major university medical center. The physician diagnosed limb-girdle MD and scheduled the boy for over 200 genetic tests. When the family contacted me, the adolescent’s history indicated a myopathy, possibly myositis. Patients who have limb-girdle MD don’t suddenly become weak after being good athletes. I referred him to the Mayo Clinic, and the workup there revealed SRP. His initial CPK there was 11,000 U/L. The boy responded well to prednisone and methotrexate and is active in sports once again.

    Emery-Dreifuss muscular dystrophy

    Emery-Dreifuss MD is an unusual muscle disorder. It is important to diagnose this disease correctly because it can cause sudden death in teenagers or adults from cardiac involvement. Insertion of a pacemaker can be lifesaving. This is a sex-linked recessive disorder, so mothers also may be at risk for cardiac problems and might need a pacemaker.

    A 10-year-old boy had been given the diagnosis of MD because of a CPK of 656 U/L and some muscle weakness. When I first examined the child, his physical exam revealed mild muscle weakness, but not in a typical pattern for Duchenne MD. A muscle biopsy, done using a local anesthetic, showed some unusual muscle cells, but no characteristics of Duchenne MD. I told the child’s mother that no definite diagnosis could be made at that time and suggested that we wait to see if any progression occurred. I followed the boy at regular intervals. He showed no increased weakness.

    Five years later, I attended a lecture by Dr. Lewis Rowland from Columbia University, New York. He presented 5 cases of a newly described disorder called Emery-Dreifuss MD.6 The symptoms and muscle biopsy were similar to my patient’s. Dr. Rowland reviewed my patient’s muscle biopsy slides and record. He confirmed it was a classic case of Emery-Dreifuss MD. The disorder can cause a severe arrhythmia that requires a pacemaker. My patient’s mother also was a candidate for a pacemaker. The boy had a pacemaker inserted as a teenager and his mother had the procedure in her early fifties. My patient died at age 52 years from cardiac problems but his mother is still living.

    NEXT: Duchenne 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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