Myopathy
Terminology
Myopathy is a diverse group of diseases/disorders that affect muscle tissues, resulting in muscle weakness, stiffness, or cramps. The term is derived from the Greek words “myo-” meaning muscle, and “-pathy,” indicating a disease or disorder.
Definition
Myopathy encompasses a broad spectrum of disorders primarily characterized by the dysfunction of skeletal muscles. It can be hereditary or acquired and varies significantly in severity and progression.
Epidemiology
The prevalence of myopathy depends on the specific type. For instance, Duchenne muscular dystrophy, a genetic myopathy, occurs in approximately 1 in 3,500 male births worldwide. Acquired myopathies, such as those induced by medications or autoimmune conditions, are more common in adults. Myopathies are found across all age groups, ethnicities, and sexes, with certain types showing a predilection for specific demographics.
Classification
Clinical Manifestations
Clinical Manifestations Patients with myopathy often experience muscle weakness that is typically proximal (e.g., thighs, shoulders), symmetric, and accompanied by fatigue, manifesting as generalized tiredness and reduced exercise tolerance. Additional symptoms may include muscle pain, cramps, or stiffness, common in inflammatory, metabolic, or toxic myopathies. Respiratory or cardiac involvement can occur in severe cases, and rashes may be present in conditions like dermatomyositis.
Patients with Duchenne muscular dystrophy (DMD) exhibit some degree of central nervous system involvement, and they have an increased risk of cognitive impairment and neuropsychiatric disorders compared to the general population.
Diagnosis
Myopathy diagnosis involves multiple approaches, including clinical, laboratory, imaging, and histopathological studies. First, the history and physical examination identify patterns of muscle weakness and associated symptoms. Laboratory tests, such as elevated creatine kinase (CK) and AST levels, indicate muscle damage. Autoantibodies may also be tested, particularly in cases of inflammatory myopathies. Electromyography (EMG) and neurography (ENG) are used to differentiate myopathy from neuropathy. Imaging techniques like MRI can detect muscle inflammation or fat replacement. A muscle biopsy provides a definitive diagnosis by revealing specific histological changes.
Additionally, EKG and echocardiography assess cardiac involvement, as cardiomyopathy may suggest underlying muscle disease. CNS-MRI ( or neuroradiologic study) is conducted to exclude neurological causes of muscle weakness or to identify central nervous system malformations associated with specific muscle diseases or myopathic syndromes.
Finally, genetic testing confirms hereditary myopathies.
Treatment
Management of myopathy depends on its underlying cause. Supportive therapy includes physical and occupational therapy and assistive devices for mobility. Pharmacological treatments may involve corticosteroids for some types of muscular dystrophies, immunosuppressants for inflammatory myopathies, and enzyme replacement therapy for metabolic disorders.
Discontinuation of causative drugs is essential in cases of toxic myopathies. Lifestyle modifications, such as regular exercise, dietary changes, and avoiding triggers, play a key role. In advanced cases, surgical interventions for contractures or scoliosis and respiratory support for muscle weakness may be necessary.
Prognosis
The prognosis of myopathies varies significantly depending on several factors, including the specific type of disease, comorbidity, and the socioeconomic conditions in which patients live.
The type of myopathy—whether genetic (e.g., Duchenne muscular dystrophy), inflammatory (e.g., polymyositis), metabolic (e.g., glycogen storage disorders), or acquired—plays a crucial role in determining disease progression, severity, and response to treatment.
The coexistence of other diseases, also known as comorbidities, significantly impacts the prognosis of myopathies. Conditions such as diabetes, cardiovascular disease, respiratory disorders, or obesity can exacerbate muscle weakness, complicate management, and accelerate disease progression. Effective prognosis requires addressing these comorbidities alongside the primary myopathy to optimize overall health outcomes and improve quality of life.
Socioeconomic status is another critical determinant influencing access to timely diagnosis, medical care, advanced therapies, and supportive services. Patients in resource-rich settings may benefit from early interventions, multidisciplinary care, physical therapy, and emerging treatments, such as gene therapy or immunomodulatory drugs. Conversely, those in resource-limited environments may face delayed diagnosis, inadequate medical support, and a lack of access to essential treatments, leading to worse outcomes.
