Duchenne Muscular Dystrophy (DMD)

Muscular dystrophy (MD) is a group of disorders characterized by progressive muscle weakness and atrophy¹.

There are different types of muscular dystrophy based on causative genetic mutations. These include congenital muscular dystrophy, Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), facioscapulohumeral muscular dystrophy (FSHD), limb-girdle muscular dystrophy (LGMD), Emery-Dreifuss muscular dystrophy, distal muscular dystrophies, and oculopharyngeal muscular dystrophy (OPMD). 

Each type of disease affects different groups of muscles and progresses at different rates affecting patients to different degrees. There are a number of complications that muscular dystrophy can cause. These include respiratory and cardiac complications and scoliosis.¹

Respiratory Complications

Most types of MD eventually affect the diaphragm and other respiratory muscles, leading to respiratory complications. Respiratory insufficiency also causes frequent lung infections, which can be life-threatening. 

The age at which respiratory problems develop varies greatly between different types of muscular dystrophy. For example, in patients with congenital muscular dystrophy, they may arise during their childhood years. In DMD, hypoventilation especially during the night is common in patients aged 15 to 20 years. Respiratory complications may not occur until later in adulthood in other forms of muscular dystrophy, such as LGMD.²

Symptoms of hypoventilation due to respiratory complication in muscular dystrophy include headaches, lethargy, and breathlessness. Respiratory complications can be diagnosed with blowing tests. A vital capacity below 60% predicted and a respiratory muscle strength below 30% of normal is indicative of hypoventilation.

In later stages of the disease, some patients need respiratory support, such as noninvasive ventilation. This could be via a BiPAP (bilevel positive airway pressure) or a CPAP (continuous positive airway pressure) machine. Both types of machines deliver pressurized air to the patient’s airways through a mask to ensure the throat muscles do not collapse and obstructions are reduced. The main difference between the 2 types of ventilators is that BiPAP machines have two settings, one for inhalation and one for exhalation to ensure more air can move in and out the patient’s lungs, whereas CPAP machines deliver a steady, continuous stream of pressurized air to the patient’s lungs. 

For patients with severe swallowing problems or those unable to use noninvasive ventilation, a tracheotomy may be necessary.

Physiotherapy and breathing exercises can also be beneficial to strengthen the respiratory muscles and aid in coughing. Some patients may need a CoughAssist machine to shift phlegm from the lungs. A cough peak flow measurement can help assess the efficiency of coughing and guide the decision regarding the need for a CoughAssist machine. In teenagers and adults, values below 270 per minute indicate weakness. Values less than 160 per minute clearance of phlegm suggest a major problem.

Patients with breathing problems should be vaccinated with influenza and pneumococcal vaccines to reduce the risk of infections. Any chest infections should be promptly treated with antibiotics.²

Cardiac Complications

Cardiomyopathy or cardiac arrhythmias are common in many forms of MD. They usually affect patients in later stages of the disease and can be life-threatening. 

Muscular dystrophies most commonly associated with cardiac complications are DMD, BMD, LGMD, and Emery-Dreifuss muscular dystrophy. Dilated cardiomyopathy occurs in almost all patients. Ventricular arrhythmias are also seen in DMD and BMD. In LGMD, RV and LV fatty infiltration and conduction disorders are common. Finally, in Emery-Dreifuss muscular dystrophy, atrioventricular conduction abnormalities, atrial standstill, atrial flutter, and atrial fibrillation can be seen.³

Electrocardiography (ECG), echocardiography are used as screening tools while cardiovascular magnetic resonance (CMR) can reveal cardiac involvement and detect muscular dystrophy-associated cardiomyopathy. Cardiomyopathy can be treated with ACE inhibitors and beta-blockers. In case of dilated cardiomyopathy or heart failure, digitalis, diuretics (furosemide), and anticoagulants are indicated.⁴

Scoliosis

Scoliosis affects many patients with muscular dystrophy and develops in almost all patients with DMD.⁵ It is caused by weakness in the muscles that support the spine and usually develops after a patient has lost the ability to stand and walk. In patients with some forms of congenital MD, scoliosis may be present from birth.⁶

Scoliosis can also have a negative impact on respiratory function as it can change the shape of the chest cavity and restrict the capacity of the lungs. 

Physiotherapy can slow the progression of scoliosis by increasing muscle strength. Spinal braces can be helpful for some patients and may delay the development of scoliosis. In cases where the progression of scoliosis is significant, scoliosis surgery may be considered.⁶ 

The timing of the scoliosis surgery depends on many factors including the patient’s age, weight, respiratory function, cardiac health, and preferences. A multidisciplinary team of health care professionals that includes a pediatrician, anesthetist, orthopedic surgeon, and nurse specialist should work together to reach a conclusion about scoliosis surgery.

Risks associated with scoliosis surgery include infections, metalwork failure, further progression of scoliosis, and prolonged paralyzation (bowels stop functioning). 

References

1. Muscular dystrophy. Mayo Clinic. Accessed May 23, 2021.
2. Simond A. Making breathing easier. Muscular Dystrophy UK. November 2011. Accessed July 11, 2021.
3. Verhaert D, Richards K, Rafael-Fortney JA, Raman SV. Cardiac involvement in patients with muscular dystrophies: magnetic resonance imaging phenotype and genotypic considerations. Circ Cardiovasc Imaging. 2011; 4(1): 67–76. doi:10.1161/CIRCIMAGING.110.960740 
4. Palladino A, D’Ambrosio P, Papa AA, et al. Management of cardiac involvement in muscular dystrophies: paediatric versus adult forms. Acta Myol. 2016; 35(3): 128–134.
5. Archer JE, Gardner AC, Roper HP, Chikermane AA, Tatman AJ. Duchenne muscular dystrophy: the management of scoliosis. J Spine Surg. 2016; 2(3):185–194. doi:10.21037/jss.2016.08.05
6. Kinali M, Barratt R. Surgical correction of spinal deformity. Muscular Dystrophy UK. December 2017.

Article reviewed by Debjyoti Talukdar, MD, on July 1, 2021.

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Ozge Ozkaya, MSc, PhD

Özge’s background is in research; she holds a MSc. in Molecular Genetics from the University of Leicester and a PhD. in Developmental Biology from the University of London. Özge worked as a bench scientist for six years in the field of neuroscience before embarking on a career in science communication. She worked as the research communication officer at MDUK, a UK-based charity that supports people living with muscle-wasting conditions, and then a research columnist and the managing editor of resource pages at BioNews Services before joining Rare Disease Advisor.