Guideline to Aid Muscular Dystrophy Diagnosis, Management

October 17, 2014

A new guideline for the diagnosis and management of patients with limb-girdle or distal muscular dystrophies has been issued by the American Academy of Neurology and the American Association of Neuromuscular & Electrodiagnostic Medicine.

The guideline, published in the October 14 issue of Neurology, should lead to a systematic approach to diagnosis and management and highlights the importance of genetic testing to identify specific types of dystrophy.

"This is the first guideline ever issued based on a systematic review of the literature that considers both limb-girdle and distal muscular dystrophies," lead author Pushpa Narayanaswami, MBBS, DM, Harvard Medical School, Boston, Massachusetts, told Medscape Medical News.

"We hope to raise awareness among both patients and physicians of the condition and the fact that there are now several genetic tests available to allow a definite diagnosis or many of these conditions," she added.

Better Quality of Life

If clinicians follow the guideline it will likely prolong the life of patients with muscular dystrophy (MD) and improve their quality of life. In large part, this would be brought about through detection and management of cardiac and respiratory complications in a timely way.

"The new guideline really emphasizes a clinical approach to diagnosis of muscular dystrophies. In that regard we do need to try to establish a genetic diagnosis in nearly all patients," said Dr Narayanaswami.

The guideline also provides algorithms for diagnosis, with the clinical picture, ethnicity, family history, and cardiac and respiratory symptoms all considered in deciding whether genetic testing for MD is appropriate and which of the many individual tests to select.

"All these factors give us clues as to the type of dystrophy the patient may have," she said.

"Sometimes clinical features will lead us straight to a genetic test. In other cases we might need to perform a muscle biopsy first to direct us to the best genetic test," Dr Narayanaswami added.

The guideline explains that the main clinical symptom of muscular dystrophies is muscle weakness that progresses very slowly. But other factors, such as age of onset and pattern of muscles affected, can vary widely between different types of MD.

Dr Narayanaswami pointed out that there is also a high degree of phenotypic variation.

"The same genetic defect can lead to different patterns of symptoms. And several different genetic defects can lead to similar symptoms," she said.

She also emphasized the importance of ruling out treatable disorders, such as Pompe's disease.

Focused Genetic Testing

While genetic tests are not yet available for every type of MD, there are tests for most of the common types such as Duchenne and Becker, myotonic and facioscapulohumeral.

There are also genetic tests for some of the less common forms, Dr Narayanaswami said, and "new genetic defects are being discovered all the time so it is somewhat of a moving target."

She stressed the importance of conducting focused genetic testing.

"When we see a patient based on the clinical picture we may suspect them to have a particular form of muscular dystrophy so we would test for that one. Others may not be so obvious, so a muscle biopsy might be a good idea to identify which protein may be deficient. This will guide us as to which genetic tests to do."

The guideline also highlights the importance of referring patients suspected of having MD to a specialist center.

Dr Narayanaswami explained that patients would probably be referred from their family doctor to a general neurologist.

"We recommend that patients are then referred on to a tertiary neuromuscular center where they will be fully evaluated and genetic testing can be performed. Once a diagnosis and a management plan have been devised, then they can be followed up by a general neurologist in their community."

She emphasized the necessity of identifying the particular dystrophy affecting each patient: "The correct diagnosis must be the goal for all patients. Genetic testing will enable this to happen."

Definitive Diagnosis

Having a definite diagnosis has many advantages, said Dr Narayanaswami. Patients know what they are dealing with and the correct management strategy can be put into place, she said.

She points out that many patients are incorrectly diagnosed with inflammatory muscle diseases and treated with immunosuppressants, which are ineffective and may be harmful.

Another advantage of correct diagnosis is that genetic counseling can be given on the risks of passing the condition on to children. Very importantly, any cardiac and respiratory complications, which occur more with some muscular dystrophies than others, can be screened for and monitored closely.

Other types of MD have a very low likelihood of cardiorespiratory involvement, so these patients can have a much lower level of screening.

While a treatment for the actual disease is not yet available in the United States, Dr Narayanaswami notes that it is vitally important to manage the cardiac and respiratory complications. These can include heart failure, rhythm disturbances, and difficulty swallowing.

"We can also recommend specific rehabilitation exercises and screen for osteoporosis and cognitive dysfunction, which can also occur with certain types of muscular dystrophies. In addition, sudden cardiac death could be reduced by identifying those patients with dystrophies associated with rhythm disorders," she added.

Neurology. 2014;83:1453-1463. Abstract

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