Muscle Disorders Overview

Dermatomyositis

• Inflammatory disorder of skin and skeletal muscle
• Unknown cause; some cases linked to cancer (e.g., stomach cancer)
• Clinical features include:
  • Bilateral muscle weakness (starts proximally, may spread)
  • Skin rash (heliotrope rash on eyelids, malar rash, Gottron papules)
• Lab findings:
  • Increased creatine kinase levels
  • Positive antinuclear antibody (ANA) and anti-Jo-1 antibody
  • Inflammatory changes (perifascicular atrophy on biopsy)
• Treatment: Corticosteroids

Polymyositis

• Inflammatory disorder of skeletal muscle
• Similar to dermatomyositis clinically, but skin is not involved
• Endomysial inflammation (CD8+ T cells) and necrotic muscle fibers seen on biopsy

X-Linked Muscular Dystrophy

• Degenerative disorder causing muscle wasting and fat replacement
• Caused by defects in the dystrophin gene
• Dystrophin is crucial for anchoring the muscle cytoskeleton to the extracellular matrix
• Mutations are often spontaneous; large gene size increases mutation risk
• Duchenne muscular dystrophy:
  • Proximal muscle weakness by age 1, progressing to distal muscles
  • Calf muscle enlargement (pseudohypertrophy)
  • Elevated serum creatine kinase levels
  • Death from cardiac or respiratory failure (heart and lungs are commonly affected)
• Becker muscular dystrophy:
  • Milder form, due to mutated dystrophin

This quiz covers various muscle disorders such as dermatomyositis, polymyositis, and X-linked muscular dystrophy. It explores their clinical features, laboratory findings, and treatment options. Dive into the complexities of these conditions and test your knowledge!