Duchenne muscular dystrophy (DMD) is a genetic muscular disorder that targets the muscles and causes them to degenerate and weaken. Statistically, around 15,000 males are affected by the condition in the U.S. alone and approximately 300,000 around the world . The most common and severe form of a muscle disorder, Duchenne, is the result of a loss of dystrophin, a protein which helps the muscle cells stay intact. It often develops early on during childhood between ages of 3 and 5. Although it primarily affects boys, there are also rare instances where girls have this condition.
Boys who developed Duchenne muscular dystrophy experience difficulties in performing even the simplest of tasks. As they grow older and the condition reaches its later stages, the muscles in the heart responsible for breathing start failing. Duchenne is primarily passed from parent to child. However, approximately 35% of DMD cases are a result of a random mutation. It simply means that anyone can be affected by this condition.
How Oedema-Fibrosis Affects Muscle Enlargement in DMD
A study conducted in 2012 has reported that an increased concentration of cytoplasmic sodium can cause oedema in Duchenne muscular dystrophy. The event tends to continue until fatty muscles have completely degenerated. During the study, they administered eplerenone to a female DMD patient. Later, they were able to determine that the drug does display beneficial effects on muscles affected with DMD.
Initially, oedema in DMD was attributed to an interstitial inflammation. However, recent studies have observed that muscle tissues in DMD patients weren’t fully replaced by fibrosis. In fact, oedema was already present even before the fatty degeneration took place. This led to the conclusion that oedema was mainly due to an increased cytoplasmic sodium concentration. The study implies that oedema is of osmotic origin and can contribute to fiber necrosis and even fibrosis in later years.
Fibrosis refers to the replacement of normal tissue with scar tissue. In other words, fibrous connective tissues have developed due to a tissue’s attempt to repair itself. Researchers were able to identify a group of cells known as fibrocytes, which could be one of the leading contributors to inflammation and fibrosis resulting in muscle loss in Duchenne.
Fibrocytes are a group of cells which help in repairing damaged muscle cells. However, they also play a role in tissue fibrosis. According to the researchers, fibrocytes which are present in damaged muscle tissues come from macrophages and monocytes that left the bloodstream. Then they end up in the muscles.
The Involvement of Cardiac Magnetic Resonance Imaging
Complications with the heart are a common occurrence in Duchenne muscular dystrophy. Even though there are certain procedures to diagnose and monitor the patients, a cardiac magnetic resonance imaging has been the standard procedure for assessing the condition. Later stages of Duchenne tend to result in end-stage heart failure from cardiomyopathy, which is becoming one of the most common causes of death in affected patients. Since it is hard to detect, a study has been conducted to examine various methods and options for the diagnosis and treatment of DMD .
Patients who suffer from Duchenne muscular dystrophy experience difficulties in walking and breathing. Eventually, they start to experience heart failure after three to four decades. However, not all who experience heart failure die. Technically, heart failure doesn’t mean the heart has failed to work. Affected patients can still continue to live long lives even with heart failure.
According to the New York Heart Association, heart failure is divided into four different levels:
- Class 1 – this is where heart function starts decreasing, although patients normally don’t have any symptoms. This occurs in patients between 10 to 15 years old.
- Class 2 – patients normally suffer from fatigue or breathlessness when doing ordinary activities. This often happens during 15 to 20 years old.
- Class 3 – patients will feel comfortable at rest, but even the slightest activities could cause symptoms.
- Class 4 – it will be difficult for the patient to perform any physical activity without experiencing discomfort. Even while at rest, the patient can still experience symptoms. This occurs in patients who are above 20 years of age.
Projecting a diagnosis on a patient with Duchenne muscular dystrophy is difficult since the progress is often slow. In fact, patients don’t display heart failure symptoms, which make evaluation and treatment a grueling process.
Cardiovascular magnetic resonance imaging has been proposed as a non-invasive procedure for assessing patients with DMD. Compared to any other modalities, MRI is known to produce high-quality images, making it useful for quantitative tissue characterization by highlighting differences in the T2 relaxation time of muscles. DMD patients have a different T2 relaxation time in their peripheral muscles as compared to healthy individuals. This finding reflects the differences in fat and water composition between healthy and affected muscles.
Since there is a variation in T2 relaxation time as DMD progresses, a cardiac MRI can be used to monitor its progression and possibly suggest therapy to the patients. In a study in 2005, it was concluded that MRI measurements of T2 relaxation time in the muscles can detect variations in the composition of tissues between DMD patients who don’t have cardio-respiratory symptoms and healthy individuals of the same age group .
Cardiac MRI vs. Echocardiography
Echocardiography has been the standard imaging modality used for assessing the presence of cardiomyopathy. The problem is, echocardiogram produces poor quality images and sometimes inaccurate evaluation of the patient's condition due to certain factors.
Not long ago, cardiac MRI has been used more frequently as a pre-operative assessment procedure for patients with Duchenne. The procedure is non-invasive and allows a three-dimensional analysis and accurate evaluation of the left ventricular ejection fraction (LVEF). Various studies have shown that an echocardiography procedure is inferior to cardiac magnetic resonance imaging in terms of early myocardial dysfunction monitoring. This suggests that a cardiac MRI may be more effective in assessing cardiac function among Duchenne muscular dystrophy patients as compared to echocardiography.
As patients with DMD age, it will be more difficult to get an accurate assessment with echocardiography. It is where a cardiac MRI proves itself to be superior. Being an effective pre-operative assessment procedure for cardiac function in DMD patients, a cardiac MRI has a few benefits to offer, including the following:
- It provides detailed, high-quality images of the heart.
- It also displays additional information such as fibrosis and preclinical cardiomyopathy.
- It provides an accurate assessment of cardiac function in Duchenne muscular dystrophy.
- It’s a non-invasive procedure and doesn’t involve the use of radiation.
However, it also has its share of drawbacks, such as the following:
- The procedure involves lying down in MRI scanner for a long period of time.
- The patient will be administered with an IV fluid.
- The operation is quite expensive.
Doctors recommend getting a baseline cardiac MRI for patients with DMD ages 8-10 years old. After a first-time procedure, it is ideal to repeat an MRI every 3-5 years.
Several studies have been able to confirm that a cardiovascular magnetic resonance imaging is an absolute necessity for people who have Duchenne muscular dystrophy. With a cardiac MRI, performing a pre-operative assessment of cardiac function in DMD patients is made more accurate. However, further studies are still required to verify the risks involved in using late gadolinium enhancement for MRI on cardiac function. Fortunately, it won’t be for long before MRI becomes widely used in assessing DMD patients worldwide.
- “Duchenne Is a Fatal Muscle Disease.” CureDuchenne www.cureduchenne.org/about/what-is-duchenne
- D'Amario, Domenico, et al. “A Current Approach to Heart Failure in Duchenne Muscular Dystrophy.” Heart, BMJ Publishing Group Ltd and British Cardiovascular Society, 1 July 2017,www.heart.bmj.com/content/early/2017/07/01/heartjnl-2017-311269.long
- Mavrogeni, S, et al. “Cardiac and Sternocleidomastoid Muscle Involvement in Duchenne Muscular Dystrophy: an MRI Study.” Chest., U.S. National Library of Medicine, Jan. 2005 www.ncbi.nlm.nih.gov/pubmed/15653975?ordinalpos=7&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum