COMPLICATIONS IN MUSCULAR DYSTROPHY
The origin and clinical symptoms vary significantly in muscular dystrophy, but the most frequently encountered complications are of musculoskeletal and neuromuscular origin which most commonly include muscle tightness, contractures, bony rotational deformities, scoliosis, reduced pulmonary and cardiac compliance. A few of these complications are secondary to immobility such as joint tightness and reduced range of motion. All of which can be easily prevented with the aid of adequate rehabilitation. Complications secondary to steroids are constipation, osteoporosis, obesity and hypertension which require medical management. In few cases weight loss and muscle fatigue can also occur in the late stages of muscular dystrophy.
The most commonly encountered complications and their management are described in detail below:
Scoliosis is a complex deformation of spine. It is a long C- shaped curve which involves the thoracic and lumbar spine. Around 75–90% of patients with Duchenne muscular dystrophy (DMD) seem to develop scoliosis due to loss of ambulation. The consequences of the deformity are loss of sitting balance, shortening of the trunk, and compression of the heart and lungs. The mobility of the ribs is reduced by rotation and deformation of the trunk, causing obstruction in breathing. An increase in deformity can also cause impairment of cardiac and/or pulmonary function. The pelvic obliquity together with weakness of the spinal musculature also impairs the sitting ability in wheelchair.
The contractures often develop as a result of various factors, including inability to move a joint through its full range of motion, static positioning in a position of flexion , muscle imbalance about a joint, and fibrotic changes in muscle tissue.
Cases with gradual progression develop more fibrosis and fatty infiltration, have severe contractures while, those with rapidly progressive conditions and neurogenic cause of muscle weakness tend to develop less severe contractures.
3. Pulmonary Complications
Pulmonary complications in muscular dystrophy majorly include chest infections, atelectasis, pulmonary hypoplasia and respiratory failure causing death. Although people with most forms of muscular dystrophy experience some deterioration of the respiratory and other skeletal muscles, respiratory involvement in DMD and CMD is inevitable. In CMD, diaphragmatic weakness is a feature even when patients are still ambulant, necessitating early respiratory monitoring. A correlation between motor and respiratory function has been observed in other sub types of CMD. The typical respiratory progression of patients with DMD is seen as an increase in vital capacity as predicted until about 10 years of age, after which it plateaus. With the development of respiratory muscle weakness along with skeletal deformities, vital capacity starts to fall. The rate at which vital capacity declines is around 8% per year. A prospective study showed that almost three quarters of patients die from hypercapnia caused due to alveolar hypoventilation.
In Myotonic dystrophy, alveolar hypoventilation is an important complication which results from a combination of respiratory muscle weakness and dysfunction of the respiratory centres in the brain. Patients are at risk of aspiration pneumonia due to failure of pharyngo-oesophageal muscle function.
Sarcoglycanopathies (LGMD 2C–2F), sub types of autosomal recessive Limb Girdle Muscular Dystrophy present respiratory involvement in more than 70% of cases with reduced forced vital capacity. In calpainopathy or LGMD 2A, there is late respiratory muscle involvement with sparing of the cardiac muscles.
Respiratory involvement is not typically observed in BMD, autosomal LGMD and distal myopathy. But, development of scoliosis, contractures and spinal rigidity, results in a restrictive pattern of respiratory impairment.
4. Cardiac Complications
Cardiac involvement in muscular dystrophy is very common in muscular dystrophy patients. It involves conduction disorders, ventricular dilatation and dilated cardiomyopathy. Loss in the integrity of the sarcolemmna, fibre necrosis and replacement of myocardium with connective tissue or fat, results in the cardiac complications. Symptoms of congestive heart failure, such as shortness of breath, fatigue, orthopnea (breathlessness which occurs when lying flat) and edema are seen with varying frequency. Over time, reduced ventricular systolic function can develop. Global or regional impairment of ventricular function can occur in the presence or absence of symptoms of congestive heart failure. Cardiac rhythm disturbances can contribute significantly to the morbidity and mortality associated with muscular dystrophy.
Cardiac involvement in DMD and BMD includes cardiomyopathy and arrhythmias. The incidence of cardiomyopathy increases with age in DMD patients. Cardiomyopathy can be evident at 10 years of age and is nearly universal in DMD patients over the age of 20. Approximately 70% of boys with BMD have cardiac involvement by age 20. Myotonic dystrophy type 1 has a multisystem affliction with prominent cardiac problems leading to an increased incidence of sudden cardiac death. There are reports of young patients with ventricular tachycardia (VT) who have no history of cardiac complaints, with phenotypic characteristics, neuromuscular testing and genetic analysis pointing towards the diagnosis of myotonic dystrophy type 1. Due to the malignant nature of VT, these patients may require an implantable cardioverter/defibrillator.
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