How Is Muscular Dystrophy Diagnosed?
A glimpse into what doctors are looking for when trying to determine whether your child has muscular dystrophy.
It's every parent's fear -- her child is missing basic developmental milestones and falling behind his peers. "He's not running as fast, he tends to be sitting a little bit more, he has a little more difficulty going up and down the stairs or getting out of chair," says Darryl De Vivo, M.D., pediatric neurologist in the Pediatric Neuromuscular Disease Center at Columbia University Medical Center/New York-Presbyterian.
The group of rare genetic diseases cause muscles to weaken and deteriorate. The most common type is Duchenne muscular dystrophy, which primarily affects young boys. With Duchenne, parents may start noticing warning signs in their child around age 2. The disease's main symptoms are late walking, enlarged calf muscles, clumsiness, frequent falls, and difficulty climbing stairs or getting up off the floor. School-age children with Duchenne may walk on the balls of their feet or their toes and have a waddling gait. Others may have trouble lifting their arms.
Many of those symptoms, however, are not linked to muscular dystrophy right away. "There are lots of reasons for delayed walking, and toe walking occurs for a number of reasons other than Duchenne muscular dystrophy, so sometimes the signs are not linked to a muscle disease," explains Valerie A. Cwik, M.D., executive vice president and chief medical and scientific officer of the Muscular Dystrophy Association in Tucson. If the connection with the disease isn't made, the doctor and parent may decide to take a wait-and-see approach.
The other challenge in diagnosing Duchenne muscular dystrophy is that it is a rare disease. "Many physicians may not have seen a lot of children with Duchenne, so it's not always the first diagnosis they think of," Dr. Cwik says.
If muscular dystrophy is suspected, the doctor will ask about family medical history and perform a basic physical. If a parent is concerned about specific symptoms, she should bring in photos and videos of the signs to show the practitioner, if possible.
Doctors typically use more than one test to diagnose muscular dystrophy, Dr. Cwik says. One of the most common tests looks for an enzyme in the blood. The exam, called a CK level blood test, measures the amount of creatine kinase. High CK levels typically indicate that muscle is being damaged. If the child hasn't had a traumatic injury, a muscular disorder is most likely to blame.
Specialists can also identify muscular dystrophy through genetic testing. By examining a blood sample, they can determine whether the child has a genetic mutation that causes muscular dystrophy. They can also tell the location of the defective gene. If the child's family history and basic physical suggest a specific type of muscular dystrophy, doctors may go straight to genetic testing for diagnosis.
When doctors are less certain about the specific cause of the symptoms, they may biopsy one of the child's muscles. The results can pinpoint whether the child's symptoms are caused by muscular dystrophy or by another muscular disorder. If muscular dystrophy is confirmed, doctors may follow up with genetic testing to confirm the specific gene and mutation, Dr. Cwik says.
If doctors suspect an infant has a specific form of the disorder called congenital myotonic muscular dystrophy, they may do an electromyography on the child's mother. This test involves putting an electrode needle into the muscle and measuring the electrical activity as the mother relaxes and tightens that muscle. Muscle disease may be detected by changes in the pattern of the electrical activity. The test is done on the mother for two reasons: First, the electrical activity consistent with the disease is not usually seen in babies. Second, congenital myotonic dystrophy is nearly always inherited from the mother, Dr. Cwik says. The results are usually also confirmed with genetic testing.
The earlier treatment begins, the better, but most boys with Duchenne muscular dystrophy aren't formally diagnosed until age 5. The Centers for Disease Control and Prevention have funded a new Web-based tool, childmuscleweakness.org, to help doctors identify muscular dystrophy and other muscular disorders earlier. Once symptoms are present, it's just a matter of doctors picking up on them, Dr. De Vivo says.
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