Physiology

• Pulmonary HTN due to neuromuscular disease (due to bilateral diaphragmatic paresis or paralysis)
• Hypoventilation leads to hypoxia/acidosis (with resultant pulmonary vasoconstriction)

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Etiology

• Polydermatomyositis (see [[Polydermatomyositis]])
• xxx

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Diagnosis

• PFT (restriction):
  • Decreased VC (due to muscle weakness, decreased lung, chest wall compliance): supine VC << upright VC (normals show approximate 20% decrease with change in position, but Bilateral Diaphragmatic Paralysis patients show >25-50% decrease)
  • Decreased TLC
  • Increased RV (due to inability to overcome recoil of chest wall outward at volumes below FRC)
  • Decreased MVV
  • Decreased MIP/ MEP
  • Decreased compliance (due to chronically low lung volumes: microatelectasis/ reduced surface tension/ altered interstitial elastic fibers)
  • Transdiaphragmatic pressure (with esophageal and gastric balloons): reveals decreased pressure gradient
• CXR: low lung volumes/ possibly aspiration pneumonia
• Diaphragmatic EMG/ NCV: may reveal myopathic changes, neuropathic changes, anterior horn cell disease

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Clinical

(usually symptomatic)

• Exertional dyspnea
• Orthopnea (due to pressure of viscera on diaphragm)
• Dullness/ decreased BS at bases
• Tachypnea (in severe disease)
• Scalene/Sternocleidomastoid contractions
• Paradoxic inward movement of abdomen with inspiration (classic)
• Respiratory failure
• Aspiration pneumonia
• Sleep-disordered breathing
• Acute/Chronic Hypoventilation (see Acute Hypoventilation, [[Acute Hypoventilation]] and Chronic Hypoventilation, [[Chronic Hypoventilation]])
• Pulmonary Hypertension/Cor Pulmonale (see Pulmonary Hypertension, [[Pulmonary Hypertension]])

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Treatment

• xxx

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References

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