<br />Introduction<br /> Myopathy refers to a heterogeneous group of neuromuscular disorders primarily affecting the skeletal muscle fibers, resulting in muscle weakness and functional impairment. Unlike neurogenic disorders that arise from dysfunction of motor neurons or peripheral nerves, myopathies are characterized by primary pathology within the muscle tissue itself. The etiology of myopathy can be broadly classified into inherited (genetic) and acquired forms, each with distinct clinical, histopathological, and molecular features.<br /><br /> Pathophysiology<br /> Myopathies involve disruption of normal muscle fiber architecture or function. Depending on the underlying cause, the muscle fibers may undergo necrosis, degeneration, inflammation, metabolic dysfunction, or abnormal protein accumulation. Elevated serum creatine kinase (CK) levels are common due to muscle fiber breakdown, and electromyography (EMG) typically shows a myopathic pattern with low-amplitude, short-duration motor unit potentials.<br /> Classification of Myopathies<br />1. Inherited (Genetic) Myopathies<br /> Muscular Dystrophies: These are progressive degenerative myopathies caused by mutations in genes encoding structural proteins of the muscle cell membrane. Examples include Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD), both linked to mutations in the dystrophin gene.<br /> Congenital Myopathies: Present at birth or early infancy, these include central core disease, nemaline myopathy, and centronuclear myopathy, often due to mutations in genes involved in sarcomere function.<br /> Metabolic Myopathies: Result from enzyme deficiencies affecting energy production, such as McArdle’s disease (myophosphorylase deficiency) or mitochondrial myopathies involving defects in oxidative phosphorylation.<br /> Channelopathies: Include periodic paralysis and myotonia caused by mutations in ion channel genes (e.g., SCN4A, CACNA1S).<br /><br />2. Acquired Myopathies<br /> Inflammatory Myopathies: Autoimmune-mediated disorders such as polymyositis, dermatomyositis, and inclusion body myositis. These conditions feature lymphocytic or macrophagic infiltration of muscle tissue, often confirmed by muscle biopsy.<br /> Toxic Myopathies: Induced by medications (e.g., statins, corticosteroids) or substances such as alcohol. They typically present with acute or subacute weakness and elevated CK.<br /> Endocrine Myopathies: Associated with hormonal imbalances such as hypothyroidism, hyperthyroidism, Cushing’s syndrome, and acromegaly.<br /> Critical Illness Myopathy (CIM): Common in ICU patients, associated with prolonged immobilization, sepsis, and corticosteroid use.<br /><br /><br /><br /> Clinical Manifestations<br />Patients typically present with proximal muscle weakness, especially affecting the pelvic and shoulder girdle muscles. Other features may include:<br />• Myalgia<br />• Muscle cramps<br />• Fatigue<br />• Gower's sign (notable in DMD)<br />• Dysphagia or respiratory muscle weakness in advanced cases<br />• Cardiomyopathy in certain dystrophies (e.g., DMD, Emery-Dreifuss muscular dystrophy)<br /><br /> Diagnostic Approach<br />A comprehensive workup for suspected myopathy includes:<br />• Serum CK: Elevated in many myopathies, especially in inflammatory and dystrophic types.<br />• Electromyography (EMG): Shows myopathic changes with small motor unit potentials.<br />• Muscle biopsy: Helps differentiate between inflammatory, dystrophic, and metabolic myopathies.<br />• Genetic testing: Crucial for inherited myopathies.<br />• MRI of skeletal muscle: Useful for identifying affected muscle groups and guiding biopsy.<br />• Autoantibody panels : Especially in autoimmune myopathies <br /><br /><br /><br /> Treatment <br />Depends on the type and cause of the myopathy. While genetic myopathies have no cure, physical therapy and supportive care can help maintain mobility. Inflammatory types often respond to corticosteroids or immunosuppressants. <br /> Prognosis<br /> The prognosis of myopathy varies widely depending on etiology. While some forms, like inflammatory myopathies, may respond well to treatment, others like Duchenne Muscular Dystrophy have a progressive course with significant morbidity and reduced life expectancy without early intervention and supportive care.<br />Dr. Zahraa Tariq Hasson<br />Al-Mustaqbal University is the number one university in Iraq.<br /><br /><br /><br /><br /><br /><br /><br /><br /><br /> <br /><br /><br /><br /><br /><br /><br /><br /><br />