Duchenne muscular dystrophy (DMD) is a genetic condition causing progressive muscle deterioration. It results from a mutation in the gene responsible for producing dystrophin, a protein that protects muscle fibers during contraction. Without functional dystrophin, muscles become fragile and are easily damaged, leading to a cycle of degeneration that outpaces the body’s repair mechanisms. This condition primarily affects boys due to its X-linked inheritance pattern, with the disorder becoming apparent in early childhood.
Early Childhood and Ambulatory Stage
The initial signs of Duchenne muscular dystrophy often appear between ages two and four. Parents may notice their son has difficulty with activities like running, jumping, or climbing stairs, which his peers manage with ease. A waddling gait or a delay in learning to walk are also common indicators of weakening muscles in the pelvis and upper legs.
A distinctive indicator is the Gowers’ sign, where a child uses his hands to “walk” up his legs to stand from a sitting or lying position. This maneuver compensates for weakness in the hip and thigh muscles. Despite this weakness, calf muscles may appear unusually large due to pseudohypertrophy, where muscle tissue is replaced by fat and scar tissue.
This period is known as the ambulatory stage because the child can still walk independently. Physical therapy, focusing on regular stretching and exercises, is used to maintain muscle strength, preserve joint flexibility, and prolong the ability to walk. Ankle-foot orthoses or splints may also be used at night to stretch the heel cords and prevent the feet from turning inward.
Adolescent and Transitional Stage
The adolescent years mark a turning point, defined by the transition to requiring a wheelchair for mobility between ages 10 and 14. This occurs as cumulative muscle damage in the legs prevents independent walking. The loss of ambulation requires adaptations in daily life, school, and home environments to accommodate wheelchair use.
Skeletal complications become more prominent during this stage. Scoliosis, a sideways curvature of the spine, frequently develops as the supporting back muscles weaken. If unaddressed, severe scoliosis can impact posture, comfort, and breathing by compressing the chest cavity.
Contractures, the tightening of muscles and tendons around joints, are also a challenge. They reduce range of motion and often affect the ankles, knees, hips, and elbows, making it difficult to straighten them fully. Physical therapy and stretching routines continue to be important for managing both scoliosis and contractures to maintain posture and joint function.
Adult Life and Systemic Complications
In adulthood, medical care shifts to managing systemic complications affecting the heart and respiratory systems. The absence of dystrophin weakens the heart muscle, leading to a condition called dilated cardiomyopathy. This causes the heart to enlarge and lose its ability to pump blood effectively. This complication is nearly universal in those with DMD and often begins developing during the teenage years without early symptoms.
The progressive weakening of respiratory muscles is another challenge. As the diaphragm and other breathing muscles become less effective, it leads to shallow breathing and difficulty coughing. An ineffective cough increases the risk of serious chest infections like pneumonia by impairing the ability to clear lung secretions. This can lead to chronic respiratory failure, where the lungs cannot adequately exchange oxygen and carbon dioxide.
Proactive monitoring is standard for managing these conditions. Regular cardiac evaluations, such as echocardiograms, track heart function, while pulmonary function tests measure breathing capacity. As breathing becomes difficult, especially during sleep, non-invasive ventilation is often introduced. A device like a BiPAP machine supports breathing and allows respiratory muscles to rest, enhancing quality of life and survival.
Factors Influencing Modern Prognosis
The prognosis for DMD has changed considerably due to advances in medical management. The use of corticosteroids, like prednisone and deflazacort, is a standard of care. These medications slow the rate of muscle degeneration, which can prolong the ability to walk by several years and delay the onset of breathing and heart problems.
Proactive cardiac and respiratory care has also impacted life expectancy. For cardiomyopathy, medications like ACE inhibitors and beta-blockers are often prescribed early to protect the heart and slow muscle damage. For respiratory care, cough-assist devices and non-invasive ventilation reduce the frequency and severity of lung infections. These interventions have helped extend life expectancy, with survival into the early 30s now more common.
Emerging therapies targeting the underlying genetic cause of DMD offer new possibilities. Technologies like exon-skipping drugs are designed to let cellular machinery “skip” the mutated gene section, enabling the production of a shorter, partially functional dystrophin protein. While not a cure, these genetic approaches aim to modify the disease’s course at a molecular level and improve the long-term outlook for those living with the condition.