Myopathy: Causes, Symptoms and Treatment
Myopathy is a disease of the skeletal muscles that causes muscle weakness and muscle loss. Causes can be genetic, inflammatory, or metabolic in origin.
Things worth knowing about "Myopathy"
Myopathy is a disease of the skeletal muscles that causes muscle weakness and muscle loss. Causes can be genetic, inflammatory, or metabolic in origin.
What is Myopathy?
Myopathy (from Greek mys = muscle, pathos = disease) refers to a group of disorders that primarily affect the skeletal muscles. Unlike neuromuscular diseases, where nerve damage leads to muscle dysfunction, in myopathy the defect lies directly within the muscle tissue itself. Those affected typically experience muscle weakness, reduced physical capacity, and in many cases progressive loss of muscle mass.
Causes
Myopathies are classified according to their underlying cause:
- Hereditary (genetic) myopathies: These include muscular dystrophies (e.g., Duchenne muscular dystrophy) and congenital myopathies caused by gene mutations.
- Inflammatory myopathies (myositis): Autoimmune conditions such as polymyositis, dermatomyositis, or inclusion body myositis, in which the immune system mistakenly attacks muscle tissue.
- Metabolic myopathies: Disorders of energy metabolism within the muscle, such as glycogen storage diseases (Pompe disease) or mitochondrial disorders.
- Toxic myopathies: Triggered by medications (e.g., statins, corticosteroids), alcohol, or other toxic substances.
- Endocrine myopathies: Associated with thyroid disorders (hypothyroidism, hyperthyroidism), Cushing syndrome, or other hormonal conditions.
Symptoms
The clinical signs of myopathy vary depending on the cause and severity. Common symptoms include:
- Muscle weakness, often symmetrical and predominantly affecting proximal muscles (those close to the trunk, such as the shoulders and thighs)
- Difficulty climbing stairs, rising from a seated position, or lifting the arms overhead
- Muscle pain (myalgia) and muscle cramps
- Increased muscle fatigue during physical activity
- In severe cases: muscle atrophy (loss of muscle mass), difficulty swallowing, or breathing difficulties due to involvement of respiratory or swallowing muscles
- In some forms: muscle stiffness or myotonia (delayed muscle relaxation)
Diagnosis
Diagnosing myopathy requires a combination of assessments:
- Medical history and physical examination: Review of symptoms, family history, and current medications
- Laboratory tests: Measurement of muscle enzymes in the blood, particularly creatine kinase (CK), which is elevated when muscle damage occurs; also inflammatory markers and autoantibodies if myositis is suspected
- Electromyography (EMG): Measurement of the electrical activity of muscles to distinguish between muscle and nerve disorders
- Muscle biopsy: Removal of a small sample of muscle tissue for histological and molecular analysis
- Imaging: MRI of the muscles to assess the extent and distribution of muscle changes
- Genetic testing: When hereditary myopathy is suspected
Treatment
Treatment is guided by the underlying cause of the myopathy:
Causal Treatment
- Inflammatory myopathies: Treatment with immunosuppressive medications such as corticosteroids (e.g., prednisone), azathioprine, methotrexate, or intravenous immunoglobulins
- Toxic myopathies: Discontinuation or substitution of the causative medication (e.g., switching statins)
- Endocrine myopathies: Treatment of the underlying hormonal condition (e.g., thyroid hormone replacement for hypothyroidism)
- Pompe disease: Enzyme replacement therapy with alglucosidase alfa
Symptomatic and Supportive Therapy
- Physical therapy: Targeted muscle training to maintain and improve muscle strength and mobility
- Occupational therapy: Provision of assistive devices and adaptation of daily activities
- Pain management: For accompanying myalgias
- Respiratory support: Non-invasive ventilation when respiratory muscles are affected
Prognosis
The prognosis depends greatly on the type of myopathy. Inflammatory and toxic forms often respond well to treatment. Hereditary myopathies are generally not curable, but consistent therapy can positively influence disease progression. Early diagnosis and treatment are critical to preventing complications and maintaining the quality of life of those affected.
References
- Engel AG, Franzini-Armstrong C (eds.): Myology. 3rd edition. McGraw-Hill, New York 2004.
- Dalakas MC: Inflammatory muscle diseases. New England Journal of Medicine, 2015; 372(18):1734-1747.
- Narayanaswami P et al.: Evidence-based guideline summary: Diagnosis and treatment of limb-girdle and distal dystrophies. Neurology, 2014; 83(16):1453-1463.
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