Meeting the challenges: pulmonary complications in Duchenne muscular dystrophy. (EP Guide To Every Body Part 8).
Duchenne muscular dystrophy (DMD) is named for the Italian neurologist who in 1861 recognized the condition as a distinct disease. However, there is considerable evidence that the disease has affected humanity for millennia. The ancient Egyptians often represented physical abnormalities realistically in their wall paintings, including individuals with physical characteristics similar to those with DMD. Other possible examples of DMD appear in Renaissance paintings. Several reasonably accurate descriptions of the disease are scattered throughout medical literature.
The muscular dystrophies are a group of inherited, progressive neuromuscular disorders classified on the basis of specific genetic characteristics. Among such conditions, Duchenne muscular dystrophy is the most common and most debilitating. Because a sex-linked recessive gene causes the disorder, it affects males almost exclusively; approximately one boy in 3,000 is born with DMD. Other, less severe forms of muscular dystrophy include Becker muscular dystrophy (BMD), Emery-Dreifuss muscular dystrophy (EDMD), facioscapulohumeral muscular dystrophy (FMD), limb-girdle muscular dystrophy (LGMD) and myotonic dystrophy (MMD). In some forms, both boys and girls may be affected.
Duchenne muscular dystrophy has been a subject of intense research efforts. In 1986, those efforts began to pay off when scientists supported by the Muscular Dystrophy Association (MDA) identified a particular gene on the X chromosome that causes the disease. They discovered that a mutation in that gene, called an alteration, results in the failure to produce dystrophin, a specific protein essential for normal muscle development. Progressive weakness and muscle deterioration result. Over time, muscle tissue is replaced with fatty tissue. In less severe forms of muscular dystrophy some dystrophin is produced, but not enough to maintain healthy muscle function. People with milder forms of muscular dystrophy typically have slower disease progression and less severe disability.
Before the introduction of prenatal screening tests, diagnosis of DMD was usually delayed until significant symptoms appeared. Because the disease is hereditary, families with one son with DMD are more alert to signs of the disorder in their other boys.
The progression of DMD is generally predictable. Typically, boys begin to show signs of muscle weakness by their third birthdays. Most are slow to start walking and, as toddlers, may begin to demonstrate enlargement of calf muscles, indicating the replacement of muscle tissue with fat. By the age of 4 or 5, children with DMD may seem uncoordinated and trip or fall frequently. They have difficulty with stairs, rising from the floor, skipping, hopping, and running. By school age, boys with DMD develop a characteristic walk. Because of weak leg muscles, they walk on their toes or the balls of their feet. To compensate for poor balance, the abdomen is thrust forward and the shoulders back.
Loss of muscle strength is steady and progressive, typically involving muscles of the lower body before those of the arms and shoulders. Limb contractures and scoliosis--or curvature of the upper spine--also develop. Sometime between ages 7 and 12, the ability to walk is lost and full-time wheelchair use becomes necessary. At around the same time, boys lose the ability to raise their arms easily. Gradually, as skeletal or voluntary muscles continue to deteriorate, activities requiring use of the arms, legs, or trunk may require assistance or mechanical support. By the early teens, signs of weakening heart and respiratory muscles appear.
Modern medical management, especially good bronchial hygiene and ventilatory support, has completely changed the life expectancy for boys and young men with DMD. Before the widespread acceptance of assisted ventilation, the majority did not reach their twentieth birthdays. Now, with conscientious attention to pulmonary health and ventilatory needs, many individuals with DMD enjoy life for several decades.
Although people with all forms of muscular dystrophy experience some deterioration of the respiratory and other skeletal muscles, breathing difficulties in DMD become progressively severe and ultimately-life-threatening. By late adolescence, most boys with DMD experience serious, recurrent pulmonary infections and increasingly frequent respiratory crises. When death occurs, it is usually a result of chronic ventilatory failure directly associated with frequent bouts of acute respiratory insufficiency arising from pneumonia, mucus plugging, or atelectasis. At least seventy-five percent of DMD deaths are a direct result of pulmonary complications.
Ironically, most boys with DMD that succumb to respiratory failure do not have impaired lungs. The direct cause of pulmonary problems is progressive deterioration and weakness of skeletal muscles, the muscles involved in swallowing and respiration, and skeletal-spinal deformities. The failure of these muscle groups interacts in complex ways to diminish pulmonary function.
Dr. John Bach, a leading authority on the treatment of neuromuscular disease, identifies breathing in and coughing out as the two most significant medical challenges in DMD. Although lung function may remain normal, the underlying disease process compromises the ability to cough effectively and to take in a deep breath.
Because of weakness of the diaphragm and the muscles of the rib cage, people with DMD cannot breathe deeply enough to take in enough oxygen to meet their needs. Deep breaths also function to expand both lung tissue and the chest wall. Without occasional expansion, the lungs and chest wall gradually stiffen, with serious consequences for lung health. If the diaphragm is weak and the chest wall too stiff to permit intake of a deep breath, the lungs cannot hold enough air to generate a cough.
Coughing plays a vital role in the maintenance of pulmonary health. Forceful expulsion of air from the lungs during a cough works to loosen, mobilize, and clear mucus and other secretions from the airways. In DMD, however, as abdominal muscles become progressively weaker, the ability to expel air with enough force to produce an effective cough is lost. Likewise, weakness of the bulbar, or throat, muscles gradually impairs the ability to cough. For a cough to take place, the flap of tissue at the top of the throat, called the glottis, must close in order for an expulsive pressure to build up inside the chest. As throat muscles weaken, the glottis ceases to close tightly. As a consequence, secretions are not cleared efficiently from the airways.
THE ROLE OF AIRWAY SECRETIONS
Normal respiratory function requires open airways to permit efficient exchange of oxygen and carbon dioxide and an effective mechanism to keep airways free of harmful pathogens. However, with each breath of air, potentially harmful substances such as dust, pollen, viruses, fungi, and bacteria may be inhaled along with vital oxygen.
Respiratory mucus plays an essential role in maintaining good respiratory health. To prevent inflammation or infection, specialized cells in the airways secrete a steady supply of mucus. Mucus is a slightly viscous fluid with mildly antimicrobial properties. The chemical and physical properties of normal mucus function to prevent or fight infection and to provide appropriate humidification in the respiratory tract. With the aid of airway cilia (small hair-like structures that move in a sweeping fashion), contaminated mucus is constantly cleared from small airways and moved toward central airways. It is then eliminated from the respiratory tract by coughing or swallowing. When mucus is cleared efficiently, respiratory infections are usually prevented.
CONSEQUENCES OF RETAINED SECRETIONS
Individuals with DMD are at high risk for pulmonary problems associated with secretion retention. Normal clearance of airway secretions requires:
* COUGH REFLEX: In DMD, as respiratory muscle weakness progresses, the ability to cough is diminished and eventually lost altogether. As a result, airway mucus accumulates and stagnates. Warm, moist mucus provides an ideal medium in which entrapped bacteria can multiply and initiate respiratory infection. In response, inflammation occurs. Increased amounts of mucus are secreted to help remove infectious substances and the toxic by-products of inflammation. When the cough reflex is ineffective, infectious mucus is retained, causing a variety of problems.
* UNOBSTRUCTED AIRWAYS: Excess mucus obstructs air passages, rendering patches of lung tissue unable to take in sufficient oxygen and to expel harmful carbon dioxide. Obstructing plugs of mucus also prevent clearance of bacteria from small airways, increasing risk for serious infection and bacterial colonization.
* FUNCTIONING MUCOCILIARY APPARATUS: Finally, large volumes of retained secretions eventually overwhelm the mucociliary apparatus, diminishing its ability to move secretions from smaller to larger central airways.
Without effective removal of retained secretions, people with DMD are caught in a spiral of progressive, and ultimately irreversible, pulmonary decline. Respiratory crises occur with increasing frequency as major airways are obstructed by mucus that cough function is too weak to clear. When respiratory failure becomes life-threatening, assisted ventilation is necessary to prevent death.
When a cure is not possible, the goal of medicine is to reduce suffering and to moderate or delay disease progression. A great deal can be done in DMD to improve quality of life and extend longevity. Interventions are focused upon the maintenance of good respiratory health. A comprehensive respiratory health treatment program for DMD should include:
AIRWAY CLEARANCE THERAPY TO PREVENT SECRETION RETENTION
Interventions for clearing the airways and improving ventilation are vital. The oldest method, chest physiotherapy (CPT) with postural drainage, can be uncomfortable and often impractical for individuals with limited mobility and significant skeletal deformity. Moreover, the method has technical limitations and physiological consequences that reduce its effectiveness. A newer technology called high-frequency chest wall oscillation (HFCWO) is rapidly becoming the method of choice for individuals with neuromuscular disease. HFCWO treatment is provided by a device called The Vest[TM] Airway Clearance System.
The Vest administers HFCWO therapy to users by means of an inflatable vest-like garment. Designed for in-home use, the method treats all segments of the lungs simultaneously. Therapy is easy. People with severe disabilities may need only minimal assistance from caregivers to don the vest, activate the controls, and provide cough assistance or routine suctioning. Many individuals with DMD can manage treatments without help. Special positioning and breathing techniques are not required. In clinical experience, The Vest has proven effective in helping clear secretions and atelectasis in individuals with and without tracheostomies. Treatment effectiveness does not depend upon the skill of either the user or a caregiver.
ASPIRATION CONTROL TO PREVENT ASSOCIATED PNEUMONIAS
Weakness of the muscles that control swallowing increases the risk of inhaling food or drink into the lungs. The problem can be minimized by performing exercises to strengthen those muscles and by taking special care while eating.
Scoliosis, or curvature of the spine, is a complication that eventually affects the majority of people with DMD. Because scoliosis prevents full expansion of the chest, the chest wall becomes stiff and breathing capacity is reduced. For some people, surgery or the use of specially designed orthotics are useful to moderate scoliosis.
MANAGEMENT OF SLEEP BREATHING DISORDERS
Frequently, individuals with DMD who breathe well during the day may experience depressed respiration while sleeping. As a result, dangerously low levels of oxygen saturation may occur, increasing risk for apnea (brief cessation of breathing). Consequences of this condition, called nocturnal hypoventilation, range from restless nights with many periods of wakefulness to incremental brain damage and even death. When medically indicated, a treatment called nasal intermittent positive pressure ventilation (NIPPV) should be started.
MANAGEMENT OF CHRONIC HYPOVENTILATION
DMD is a progressive disease; eventually, life cannot be sustained without permanent ventilatory assistance. With timely introduction of assisted ventilation, life expectancies in DMD continue to improve and the majority of users report that their quality of life remains good.
NON-INVASIVE VENTILATORY SUPPORT
Although eventually all those with DMD require full-time invasive ventilation, several non-invasive methods have been introduced. Most notable is nasal intermittent positive pressure ventilation (NIPPV), which can maintain people with DMD for up to several years. As noted above, NIPPV is used to manage nocturnal hypoventilation and may be used 24 hours daily as respiratory decline progresses. In addition to quality of life advantages, studies demonstrate significant reductions in morbidity and hospitalization rates and impressive increases in survival among people with DMD receiving non-invasive ventilatory support. However, for NIPPV to be effective, adequate airway clearance is essential. Retained secretions and recurrent infections exacerbate existing poor gas exchange and sleep-related hypoxemia (insufficient oxygen). Airway clearance is of critical importance during episodes of upper respiratory tract infection.
ASSISTED VENTILATION VIA TRACHEOSTOMY
Unfortunately, despite non-invasive ventilatory support, people with DMD experience a progressive decline in pulmonary function and bulbar muscle strength, resulting in problems such as recurrent aspiration. When individuals are unable to clear secretions or obstructions from the respiratory tract sufficiently to maintain open airways, tracheostomy (insertion of an artificial airway) is required. However, although artificial airways are intended to keep airways open, their presence may also contribute to ineffective secretion clearance as a result of their adverse effect on normal airway clearance mechanisms. Consequently, regular airway clearance therapy plays a vital role in the maintenance of people with tracheostomies who are ventilator-dependent. Many people who elect ventilator dependence via an artificial airway experience both increased survival and, on the whole, a satisfactory quality of life.
LIVING WITH DMD
Today, most people with chronic illnesses and physical disabilities want to be accepted as self-directed individuals willing and able to take their rightful place in the mainstream of community life. With the assistance of well-managed medical care, many boys and young men with DMD are able to adapt to their physical disabilities and live satisfying lives.
QUALITY AIRWAY CLEARANCE THERAPY SHOULD:
* Clear secretions effectively and consistently
* Preserve lung function
* Reduce infectious exacerbations
* Reduce dependence upon antibiotic therapy and other medications
* Reduce need for hospitalization and auxiliary medical services
* Delay disease progression
* Reduce the burden of care
* Enhance quality of life
* Eat a well-balanced diet. Because physical exercise is limited, individuals with DMD are at high risk for becoming overweight. Extra weight increases the demand on respiratory muscles, and limits the effectiveness of cough assistance and certain forms of ventilatory support. In addition, larger bodies require more oxygen.
* Drink plenty of fluids. Keeping well hydrated helps keep lung secretions thin and therefore easier to clear.
* Avoid exposure to second hand smoke, environmental hazards, and large crowds.
* Receive annual flu and pneumonia immunizations.
* Avoid sedatives, cough suppressants, and alcoholic beverages, especially at bedtime.
by James Derivan It became apparent that I had Duchenne muscular dystrophy (DMD) when I was 7 years old. I began having frequent pain in my calf muscles. At first my parents treated the pain with aspirin, heating pads, and massage of my calves, but were quick to sense that something serious might be wrong. I was soon diagnosed with DMD. My parents faced raising a child with a serious and incurable physical condition. The only help in slowing the deterioration of my muscle tissue would be physical therapy; staying active would help me maintain my strength for as long as possible.
That was exactly what my parents had me do. As much as I disliked doing my exercises, they were done every night. It was hard to see, though, that the pain caused by physical therapy would ever be beneficial. It must have been even harder on my parents to inflict that pain on me, even though it was helpful.
There were easier ways to keep me active, however. Seeing my strong interest in sports, especially the New York Yankees, my parents encouraged me to participate. They signed me up to play baseball and, later, soccer. I remember my father taking me to baseball fields and teaching me how to hit, giving me the nickname "Mickey," for his favorite player, Mickey Mantle. Playing catch every day after he got home from work became a ritual for us.
My parents encouraged me in other areas as well. In grade school I joined the Fife and Drum Band. I learned the fife and participated in some parades. My mother's focal point was education and socialization. She knew that my physical disability had nothing to do with the ability of my mind. She instilled in me the confidence to get my education through high school and eventually obtain a BA in journalism from Marist College.
My mother also gave me the courage to make friends despite my difference from most schoolmates. At every level of school, I made good friends who never made me feel different. She and my father encouraged me to become involved in school activities. In high school I was a statistician for the football, basketball, and baseball teams. This opened the door for me to make friends. In college I wrote for the newspaper and became a DJ on the radio. Her emphasis on socialization remained with me. My mother has passed away, but her influence will never fade.
CORRECTION: November's issue was Part 7 in this series and was mistakenly numbered Part 8. This month is Part 8. We regret any confusion this error may have caused.
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|Publication:||The Exceptional Parent|
|Date:||Dec 1, 2001|
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