Myopathy

Definition

Myopathy refers to a group of diseases characterized by muscle weakness due to problems originating in the muscle fibers themselves, rather than from nerve dysfunction. It generally involves muscle degeneration, inflammation, or metabolic abnormalities.

Causes

• Genetic: Muscular dystrophies (e.g., Duchenne, Becker)

• Inflammatory: Polymyositis, dermatomyositis

• Metabolic: Mitochondrial myopathies, glycogen storage diseases

• Toxic: Due to drugs (e.g., steroids, statins), alcohol

• Endocrine: Thyroid disease, Cushing’s syndrome

• Infectious: Viral, bacterial infections affecting muscles

Symptoms

• Muscle weakness (often proximal muscles like hips, shoulders)

• Muscle cramps or stiffness

• Fatigue on exertion

• Muscle pain (less common)

• Difficulty climbing stairs, lifting objects, or rising from a chair

Types of Myopathy

• Inherited Myopathies: Muscular dystrophies, congenital myopathies

• Inflammatory Myopathies: Polymyositis, dermatomyositis, inclusion body myositis

• Metabolic Myopathies: Disorders of muscle metabolism (e.g., mitochondrial diseases)

• Toxic Myopathies: Due to drug or toxin exposure

• Endocrine Myopathies: Secondary to hormonal imbalances

Diagnosis

• Clinical history and physical exam

• Blood tests (elevated creatine kinase [CK])

• Electromyography (EMG)

• Muscle biopsy

• Genetic testing (for inherited forms)

• MRI of muscles (sometimes)

Treatment

• Depends on cause:

  • Inherited: Supportive care, physical therapy

  • Inflammatory: Immunosuppressants (steroids, methotrexate)

  • Metabolic: Dietary modifications, supplements

  • Toxic: Stopping offending drugs/toxins

  • Endocrine: Treat underlying hormone imbalance

Prognosis

Varies widely based on type and severity; some are slowly progressive, others more severe.