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WASTING > WEAKNESS

• Pathology is often Type II muscle fiber atrophy.
  • Cachexia (weight loss > 15%)
  • Aging
  • Disuse
  • Endocrine myopathies: Corticosteroid excess; Hyperthyroidism
  • Paraneoplastic Neuromyopathy
• Other disorders with prominent wasting associated with weakness
  • Congenital myopathies
  • Congenital myasthenic syndromes
  • Denervation
  • HIV wasting

METABOLIC CHANGES IN SYSTEMIC DISORDERS WITH MUSCLE WASTING

• Metabolic changes (Low CG syndrome)
  • Low plasma cystine & glutamine
  • High plasma glutamate
  • Low intracellular glutathione
  • High urea production
• Weight loss
  • Selectively in skeletal muscle
  • Not prevented by aggressive nutrition
• Natural killer cell function: Reduced
• Syndromes with low plasma cystine & glutamine levels
  • HIV: Late asymptomatic stage
  • Sepsis & trauma
  • Bowel disease: Crohn's; Ulcerative colitis
  • Chronic fatigue syndrome
  • Overtraining
• Changes may be reversed by N-acetyl-cystine (NAC) treatment
• Differs from starvation which has
  • Low urea production
  • Weight loss in most organs

Congenital myopathy Severe wasting involves the distal arms & legs. The most distal regions, the hands & feet, are relatively spared

Chronic denervation: Severe Severe wasting involves the distal arms & legs including the most distal regions, the hands & feet. Note atrophy of median (thenar) and ulnar innervated muscles in the hands. Severe trophic skin changes are present on the legs.