Skeletal myopathy is a general term for diseases that directly affect skeletal muscles, the voluntary muscles responsible for movement and connecting to bones. These conditions cause muscle weakness and impaired muscle function, differing from issues affecting nerves or joints. Myopathy directly impacts muscle fibers, disrupting their ability to contract and relax properly.
Understanding Skeletal Myopathy
Skeletal myopathy involves damage or dysfunction of muscle fibers. At a cellular level, this can include abnormalities in the muscle’s structure or metabolism. Problems may arise from muscle fiber degeneration or issues with components needed for normal muscle function. When muscle fiber bundles are damaged or defective, the muscle cannot work effectively, leading to weakness.
Diverse Forms of Skeletal Myopathy
Skeletal myopathies are broadly categorized into inherited and acquired forms. Inherited myopathies result from genetic mutations passed down through families, affecting muscle function from birth or developing later in life. Acquired myopathies develop due to external factors or underlying health conditions.
Inherited Myopathies
Inherited myopathies include:
Muscular dystrophies, such as Duchenne and Becker muscular dystrophies, which involve progressive muscle weakness.
Congenital myopathies, present at birth or in early childhood, can cause developmental delays in motor skills like crawling or walking and generally do not worsen over time.
Metabolic myopathies, like Pompe disease or McArdle disease, result from genetic defects in enzymes necessary for muscle function and can lead to exercise intolerance or muscle pain.
Mitochondrial myopathies are caused by mutations in mitochondria, the energy-producing parts of cells, and may also affect the brain, heart, or gastrointestinal system.
Acquired Myopathies
Acquired myopathies stem from non-genetic causes and include:
Inflammatory myopathies, such as polymyositis, dermatomyositis, and inclusion body myositis, occur when the body’s immune system attacks its own muscle fibers, causing inflammation.
Toxic myopathies can be induced by certain medications, like statins, or substances like alcohol.
Endocrine myopathies are linked to hormonal imbalances, such as those seen in thyroid disorders.
Critical illness myopathy can develop in individuals in intensive care units, potentially due to prolonged immobility or certain medications like corticosteroids, affecting respiratory muscles.
Common Indicators
Skeletal myopathy presents with progressive muscle weakness, affecting both sides of the body symmetrically. This weakness appears first in the proximal muscles, those closer to the center of the body, such as the shoulders, upper arms, hips, and thighs. This can make activities like climbing stairs, rising from a chair, or lifting objects above the head challenging.
Individuals may also experience muscle pain, tenderness, stiffness, or cramps. Fatigue, particularly after physical activity, is another symptom, leading to a general lack of energy. While proximal muscles are primarily affected, some myopathies can also impact muscles in the hands, feet, face, or those involved in breathing and swallowing, potentially causing slurred speech or difficulty eating.
Identifying and Addressing Skeletal Myopathy
Diagnosing skeletal myopathy begins with a thorough physical examination and a detailed review of the patient’s medical history, including any family history of muscle disorders. Initial blood tests include checking levels of creatine kinase (CK), an enzyme elevated when muscle fibers are damaged. Other blood tests may assess electrolyte levels or thyroid function to rule out other conditions.
Electromyography (EMG) and nerve conduction studies (NCS) are diagnostic tools that measure the electrical activity of muscles and nerves, helping to differentiate between muscle and nerve disorders. Muscle biopsy, involving the surgical removal of a small muscle tissue sample for microscopic examination, can reveal specific muscle fiber changes, inflammation, or abnormal protein accumulation. Genetic testing is performed for suspected inherited forms to identify specific gene mutations. Magnetic resonance imaging (MRI) of the muscles can be used to assess the extent of muscle involvement and identify areas of damage.
Managing skeletal myopathy involves a multidisciplinary approach tailored to the specific type and individual needs. While many inherited myopathies do not have a cure, treatment focuses on symptom management and improving quality of life. Physical and occupational therapy are important, aiming to maintain muscle strength, improve flexibility, and enhance overall mobility for daily activities.
Medications vary by myopathy type. For inflammatory myopathies, corticosteroids like prednisone or immunosuppressants such as methotrexate may be prescribed to reduce inflammation and modulate the immune response. Enzyme replacement therapy is available for some metabolic myopathies, such as Pompe disease. For acquired forms, addressing the underlying cause is key, which might involve discontinuing offending drugs, treating endocrine disorders, or managing infections. Supportive care, including pain management and assistive devices, also plays a role in improving function and comfort.