Testing and Diagnosis

Making an initial diagnosis starts with a complete family history and physical examination. A person will also undergo a battery of medical tests, depending on the symptoms he or she is having. A key element of the evaluation is electromyography (EMG). This procedure detects the presence of myotonia in a high proportion of people with DM1 or DM2. When test results point strongly toward a diagnosis of myotonic dystrophy, the disorder can be confirmed by genetic testing. 

The genetic test requires a blood sample from the patient. The DNA is extracted from the blood sample and analyzed to see if that person has the DM mutation. Prenatal testing, where the DNA of the fetus is checked for the presence of the myotonic dystrophy mutation, is also available. 

Diagnosis of myotonic dystrophy is not difficult once the disorder is suspected. However, the path to a correct diagnosis of myotonic dystrophy can be long and complex, and delays in diagnosis are very common. It can typically take over 6 years to reach a diagnosis of DM1 and up to 11 years to confirm DM2.

To a print-ready version of the following information click on the printer icon above or see the MDF Toolkit.

Genetic Testing

Genetic testing (also referred to as DNA testing) is a definitive diagnostic of whether or not a person has DM. DNA, the genetic material in the nucleus of cells, is isolated from a sample of blood or other tissue, and then analyzed to determine whether or not a specific mutation is present. 

Genetic testing is available for DM1 using standard DNA diagnostic protocols (PCR and southern blot) to confirm the presence of DM. 

Genetic testing is also available for the diagnosis of DM2 using standard DNA diagnostic protocols. However, in some cases the repeat expansion for DM2 may be too large for PCR testing. In those instances, southern blot techniques are used for diagnosis. 

Reasons to Consider Genetic Testing

Genetic testing can be beneficial in the following situations:

  • A confirmed diagnosis can eliminate the need for additional medical tests and reduce anxiety about the cause of symptoms. 
  • People with DM should be educated about the dangers of anesthesia and alert their doctors should they ever need surgery. 
  • Couples can make family planning decisions based on their genetic risk. 
  • Mothers with DM1 can have special monitoring during pregnancy and prepare for risks involved for a child born with congenital DM.

Concerns about Asymptomatic Testing

There are three explanations as to why some individuals with myotonic dystrophy might not show symptoms of the disease:

  • Symptoms may be so mild these individuals do not realize they have the disorder.
  • They may have a late onset form of the disease and do not yet exhibit symptoms.
  • They may carry a pre-mutation (a form of the mutation that is less extensive than that seen in patients who display symptoms). These individuals are not likely to develop disease symptoms, but their children are at risk of inheriting the mutation and having the disorder. 

Testing when symptoms are not present is not as straightforward. Some problems that may arise from a diagnosis of DM include:

  • Difficulties in obtaining insurance, such as health, disability and life
  • Prejudice in the workplace or elsewhere
  • Impact of being diagnosed with a disorder when no cure or treatment capable of slowing the progression of myotonic dystrophy currently exists.

Obstacles to Getting a Diagnosis

Since the symptoms of DM often mimic more common diseases, many potential causes need to be ruled out through medical testing. Medical professionals are often unfamiliar with DM since they see these cases so infrequently. Selection of the appropriate genetic test many not be obvious since there are more than thirty genetic distinct forms of muscular dystrophy. In the case of myotonic dystrophy, diagnosis is complicated even further by the variability of the disease. Some of the confounding issues include:

  • Myotonic dystrophy can take multiple forms that affect a broad spectrum of systems. Individuals may visit several different specialists for disparate symptoms, such as an ophthalmologist for blurred vision, a gastroenterologist for stomach pain, and a cardiologist for an abnormal heartbeat. These individual physicians may not be aware of their patient's full range of problems and therefore may not be able to put the pieces together for an accurate diagnosis. 
  • The severity of symptoms can vary greatly, even within the same family. Quite often individuals go to their primary care physician with a variety of complains, most so general that the doctor never suspects any serious problem. As a result, a correct diagnosis may be delayed until the disease has progressed significantly.  

Diagnosis

Genetic Tests

Genetic testing (also referred to as DNA testing) is a definitive diagnostic of whether or not a person has DM. DNA, the genetic material in the nucleus of cells, is isolated from a sample of blood or other tissue, and then analyzed to determine whether or not a specific mutation is present. 

Genetic testing is available for myotonic dystrophy DM1 using standard DNA diagnostic protocols (PCR and southern blot) to determine definitively whether or not an individual has myotonic dystrophy. Genetic testing is also available for DM2 using standard DNA diagnostic protocols, however, the repeat expansion may be too large for PCR testing in some cases. In those instances, southern blot techniques are used for diagnosis.

Genetic testing can be beneficial in the following situations:

  • A confirmed diagnosis can eliminate the need for additional medical tests and reduce anxiety about the cause of symptoms. 
  • People with DM should be educated about the dangers of anesthesia and alert their doctors if they should need surgery.
  • Couples can make family planning decisions based on their genetic risk.
  • Mothers with DM1 can have special monitoring during pregnancy and prepare for risks involved for a child born with congenital DM.

Systemic Problems

A range of diagnostic tests are used to identify problems related to affected body systems. In the absense of genetic testing, electromyography (EMG) is a highly effective diagnostic tool for identifying myotonic dystrophy in a high proportion of people with DM1 and DM2. (See Neuromuscular Assessment in the MDF Toolkit.)

For a print-ready version of this information click the printer icon above or see the MDF Toolkit.