M04.05.07 Summation and Recruitment

Muscle disorders and diseases encompass a wide range of conditions that affect muscle function and structure. Understanding these disorders is critical for medical students as they provide insight into diagnosing, managing, and treating patients with muscular issues.

Muscular Dystrophies

Overview:

• A group of genetic disorders characterized by progressive muscle weakness and degeneration.
• Common types include Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy (BMD).

Key Features:

• Duchenne Muscular Dystrophy (DMD):
  • X-linked recessive disorder.
  • Onset in early childhood.
  • Rapid progression of muscle weakness.
  • Gower’s sign and pseudohypertrophy of calf muscles.

• Becker Muscular Dystrophy (BMD):
  • Milder form compared to DMD.
  • Later onset and slower progression.
  • Similar symptoms but less severe.

Diagnosis and Management:

• Genetic testing and muscle biopsy.
• Management includes physical therapy, corticosteroids, and supportive care.

Points to Remember:

• Early diagnosis is crucial for better management.
• Genetic counseling is important for affected families.

Myopathies

Overview:

• A heterogeneous group of muscle diseases with various etiologies, including inflammatory, metabolic, and congenital origins.

Types:

• Inflammatory Myopathies:
  • Polymyositis and dermatomyositis.
  • Immune-mediated muscle inflammation.
• Metabolic Myopathies:
  • Due to defects in muscle energy metabolism.
  • Examples include McArdle disease and Pompe disease.
• Congenital Myopathies:
  • Present at birth.
  • Include conditions like central core disease and nemaline myopathy.

Diagnosis and Management:

• Muscle biopsy, electromyography (EMG), and genetic testing.
• Treatment varies based on type but often includes immunosuppressants for inflammatory myopathies and enzyme replacement therapy for metabolic myopathies.

Points to Remember:

• Recognizing clinical patterns helps in narrowing down the diagnosis.
• Muscle biopsy remains a gold standard for many myopathies.

Neuromuscular Diseases

Amyotrophic Lateral Sclerosis (ALS):

Overview:

• A progressive neurodegenerative disorder affecting motor neurons.
• Leads to muscle weakness, atrophy, and eventually respiratory failure.

Key Features:

• Mixed upper and lower motor neuron signs.
• Fasciculations, spasticity, and hyperreflexia.

Diagnosis and Management:

• Clinical diagnosis supported by EMG.
• Riluzole and edaravone can slow disease progression.
• Multidisciplinary care is essential.

Myasthenia Gravis (MG):

Overview:

• An autoimmune disorder characterized by antibodies against acetylcholine receptors at the neuromuscular junction.

Key Features:

• Fluctuating muscle weakness and fatigability.
• Ptosis, diplopia, and generalized weakness.

Diagnosis and Management:

• Acetylcholine receptor antibody testing.
• Treatment includes acetylcholinesterase inhibitors, immunosuppressants, and thymectomy.

Points to Remember:

• Early recognition and treatment are key to improving outcomes.
• Differentiating between ALS and MG can be challenging but is critical for management.

Common Muscle Injuries and Their Management

Types:

• Strains and Sprains:
  • Overstretching or tearing of muscle or tendon.
  • Common in athletes and active individuals.
• Tendonitis:
  • Inflammation of tendons due to overuse.
  • Common sites include the shoulder, elbow, and Achilles tendon.

Management:

• RICE protocol (Rest, Ice, Compression, Elevation) for acute injuries.
• Physical therapy and rehabilitation exercises.
• Anti-inflammatory medications.

Points to Remember:

• Proper warm-up and stretching can prevent many muscle injuries.
• Gradual return to activity is important to prevent re-injury.

Table: Overview of Key Muscle Disorders

Takeaway Points to Remember:

• Recognizing clinical features and patterns is crucial for diagnosing muscle disorders.
• Genetic testing and muscle biopsy are key diagnostic tools.
• Multidisciplinary management is often required for optimal patient care.
• Early intervention can significantly improve outcomes in many muscle disorders.

Bibliography:

1. Engel, A. G., & Franzini-Armstrong, C. (2004). Myology. McGraw-Hill.
2. Darras, B. T., Jones, H. R., & Ryan, M. M. (2014). Neuromuscular Disorders of Infancy, Childhood, and Adolescence: A Clinician’s Approach. Elsevier.
3. Amato, A. A., & Russell, J. A. (2016). Neuromuscular Disorders. McGraw-Hill.
4. Dalakas, M. C., Hohlfeld, R., & Engel, W. K. (2003). Polymyositis and Dermatomyositis. Springer.
5. Mitsumoto, H., & Munsat, T. L. (2001). Amyotrophic Lateral Sclerosis: A Guide for Patients and Families. Demos Medical Publishing.
6. Pascuzzi, R. M. (2015). Myasthenia Gravis and Related Disorders. Springer.