Poliomyelitis

Etiology

  • Polio virus
  • Virus destroys the anterior horn motor neurons in the spinal cord

Physiology

  • Pulmonary HTN due to neuromuscular disease
  • Hypoventilation leads to hypoxia/ acidosis (with resultant pulmonary vasoconstriction)
  • Ventilatory response to hypercapnia is decreased (related to the reduction in VC and MVV) while ventilatory response to hypoxia is relatively preserved

Diagnosis

  • ABG: hypoxemia/ hypercapnia
  • PFT’s: restriction
    • Decreased VC (typically 40-70% predicted/ due to muscle weakness, decreased lung compliance, and decreased chest wall compliance): characteristically lower VC for a given level of respiratory muscle strength compared to other neuromuscular diseases (probably due to more aggressive current treatment of pulmonary complications of polio)
    • Decreased TLC
    • Increased RV (due to inability to overcome recoil of chest wall outward at volumes below FRC)
    • Decreased MVV
    • Decreased MIP/MEP
    • Decreased lung compliance (due to chronically low lung volumes: microatelectasis/ reduced surface tension/ alteration in elastic fibers in lung interstitium)
  • CXR: low lung volumes
  • EMG: dennervation potentials/ giant motor units
  • NCV: normal

Clinical

  • Acute/Chronic Hypoventilation (see Acute Hypoventilation, [[Acute Hypoventilation]] and Chronic Hypoventilation, [[Chronic Hypoventilation]])
    • Muscle Weakness/Paralysis (of limbs, truncal, and respiratory muscles) are most severe in early febrile stage of disease
    • Significant respiratory muscle weakness occurs in 15% of cases (from 1953 epidemic): distribution and severity is variable (usually, inspiratory > expiratory muscle weakness)
    • Partial recovery (due to recovery of anterior horn cells or improved function of unaffected muscles) during convalescence
  • Kyphoscoliosis
  • Aspiration Pneumonia
  • Sleep-Disordered Breathing
  • Pulmonary Hypertension/Cor Pulmonale: due to chronic hypoventilation

Post-Polio Syndrome

  • Denervation of previously reinnervated muscles
  • Generally involves same muscle groups that were previously affected
  • Occurs 20-30 years after recovery from primary disease

Treatment

  • Prevention: polio vaccine
  • Mechanical ventilation: may be required
    • Ventilatory endurance time (time that patient is able to breathe without ventilator) is linearly related to VC
    • Corrects polycythemia but does not improve work of breathing, lung compliance, or MVV
  • Glossopharyngeal breathing: see Amyotrophic Lateral Sclerosis [[Amyotrophic Lateral Sclerosis]])

References

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