Progressive muscular dystrophy is a group of chronic, progressively worsening hereditary primary skeletal muscle disorders. It predominantly occurs in children and adolescents, with clinical features including chronic, progressive, symmetrical muscle weakness and atrophy in selectively affected skeletal muscles, sometimes accompanied by pseudohypertrophy. This condition is a monogenic inherited disease, with different inheritance patterns for various types. For example, the pseudohypertrophic type (Duchenne type) is X-linked, with the pathogenic gene located on the short arm of the X chromosome (Xp21). Consequently, females are carriers while males manifest the disease. The pathogenic gene has been isolated and cloned.

bubble_chart Clinical Manifestations

This group of diseases encompasses various types, each characterized by distinct ages of onset, inheritance patterns, and affected muscles. The clinical manifestations of muscle involvement in different regions are as follows: When the pelvic girdle muscles are affected, patients walk slowly with a waddling gait resembling a duck, have difficulty climbing stairs, and struggle to stand up after squatting. Rising from a supine position is challenging, requiring them to first turn prone and then use their hands to support their lower limbs while gradually straightening their torso to stand—a phenomenon known as a positive Gower's sign. If weakness in the hip flexors/extensors and knee extensors worsens, maintaining an upright posture becomes impossible, necessitating a wide stance for stability. Walking on tiptoes increases the risk of falling. When the serratus anterior, trapezius, and rhomboid muscles weaken, raising the arms causes the medial scapula to protrude from the chest wall like wings, termed "winged scapula." If the latissimus dorsi is involved, lifting the child by the armpits results in the arms sliding upward, bringing the shoulders close to the ears. Facial muscle involvement, particularly the orbicularis oris and orbicularis oculi, leads to expressionless facies, difficulty closing the eyes, raising eyebrows, or frowning. If extraocular muscles are affected, ptosis occurs, eye movement becomes restricted, and in severe cases, the eyes may become fixed. Pharyngeal muscle involvement causes swallowing, breathing, and speech difficulties. If the diaphragm or intercostal muscles are affected, respiratory distress ensues. Some cases exhibit pseudohypertrophy, most notably in the gastrocnemius. A subset of patients may also have cardiomyopathy, and a few may present with mild intellectual disability (Grade I).

1. Increased serum creatine phosphokinase (CPK) activity: Pseudohypertrophic type shows significant elevation, sometimes up to several hundred times higher, while other types exhibit grade I to grade II increases.
2. Electromyography: Reveals myogenic damage. During muscle relaxation, insertion potential decreases; during grade I contraction, motor potential duration shortens with low amplitude; polyphasic waves significantly increase, and short spike waves or polyphasic potentials may appear. Pathological interference patterns occur during maximal contraction. Fibrillation potentials are rarely observed in this disease. Motor and sensory nerve conduction velocities remain normal.
3. Muscle histopathological examination: Shows muscle fiber necrosis and connective tissue proliferation. This examination can exclude other myopathies.
4. Measurement of dystrophin content in muscle tissue: Immunofluorescence staining with dystrophin antibodies is used to determine the presence of dystrophin in the patient's muscle. Complete absence confirms pseudohypertrophic muscular dystrophy. If dystrophin is present but exhibits abnormal total amount or molecular weight, it may indicate Becker-type muscular dystrophy.
5. Genetic diagnosis: Polymerase chain reaction is applied.