Phrenic Neuropathy

Etiology

Infection/Toxin

Other

  • Acute Intermittent Porphyria (see Acute Intermittent Porphyria)
  • Chronic Inflammatory Demyelinating Polyneuropathy (see Chronic Inflammatory Demyelinating Polyneuropathy)
  • Critical Illness Polyneuropathy (see Critical Illness Polyneuropathy and ICU-Acquired Weakness)
  • Diabetic Neuropathy (see Diabetic Neuropathy)
  • Guillian-Barre Syndrome (see Guillian-Barre Syndrome): acute or subacute
    • Ascending paralysis (similar to tick paralysis and in contrast to descending paralysis seen in botulism and paralytic-neurotoxic shellfish poisoning)
  • Hypothyroidism (see Hypothyroidism)
    • Hypothyroidism-associated chronic hypoventilation is due to a combination of neuropathy, myopathy, and decreased drive
  • Idiopathic Peripheral Neuropathy
  • Mediastinal/Esophageal Surgical Injury or Traumatic Injury of Bilateral Phrenic Nerves
    • Phrenic nerve injury occurs in 2-20% of open heart surgery cases
    • L>R sided injury
    • Mechanisms: cold cardioplegia, dissection of LIMA, and/or stretching of phrenic nerve
  • Multiple Sclerosis (see Multiple Sclerosis)
  • Neurofibromatosis (see Neurofibromatosis): case report of bilateral diaphragmatic paralysis
  • Systemic Lupus Erythematosus (SLE) (see Systemic Lupus Erythematosus): neuropathy with vasculitis of phrenic nerves + myopathy

Physiology

  • Acute Phrenic Neuropathy
    • Prior unilateral paralyzed or paretic hemidiaphragm with new contralateral paralyzed or paretic hemidiaphragm -> resulting in bilateral diaphragmatic dysfunction
    • Acute bilateral paralyzed or paretic bilateral hemidiaphragms
  • Chronic Phrenic Neuropathy
    • Chronic bilateral paralyzed or paretic hemidiaphragms
  • Bilateral phrenic neuropathy (with bilateral diaphragmatic dysfunction) -> acute or chronic hypoventilation leads to hypoxia + acidosis (with resultant pulmonary vasoconstriction)

Diagnosis

  • ABG
    • Hypoxemia and hypercapnia
  • PFT’s: restriction
    • Decreased FEV1 (about 50% predicted)
    • Decreased VC (about 45% predicted/ due to muscle weakness, decreased lung and chest wall compliance): supine VC usually <50-75% of upright VC
    • Decreased TLC,RV,FRC
    • Decreased MVV
    • Decreased MIP
    • Decreased lung compliance (due to chronically low lung volumes: microatelectasis/reduced surface tension/altered interstitial elastic fibers)
    • Transdiaphragmatic pressure: using NG balloon (Pga-Pes)/normal change >25 cm H2O (referenced to TLC), usually 2-20 cm H2O in bilateral paralysis
  • CXR/Chest CT
    • Low lung volumes
    • Elevated diaphragms
  • Sniff Test
    • Paradoxic motion of diaphragms (normal in some cases due to expiratory abdominal muscle contraction with upward diaphragm motion, passive inspiratory downward movement)
  • Diaphragmatic EMG/NCV
    • Evidence of neuropathy (rules out myopathy and anterior horn cell disease)
  • Phrenic Nerve Stimulation
    • Using percutaneous and needle electrodes -> follow diaphragm motion

Clinical Features

  • Severe Exertional Dyspnea (see Dyspnea, [[Dyspnea]])
  • Orthopnea (see Orthopnea, [[Orthopnea]]): due to pressure of viscera on diaphragm
  • Dullness/Decreased Breath Sounds at Bases
  • Tachypnea
  • Prominent Scalene/Sternocleidomastoid Contractions
  • Paradoxic Inspiratory Inward Movement of Abdomen: classic sign
  • Atelectasis (see Atelectasis, [[Atelectasis]])
  • Aspiration Pneumonia
  • Sleep-Disordered Breathing: nocturnal hypoxemia, nocturnal hypercapnia, etc
  • Acute/Chronic Hypoventilation (see Acute Hypoventilation, [[Acute Hypoventilation]] and Chronic Hypoventilation, [[Chronic Hypoventilation]])
  • Pulmonary Hypertension/Cor Pulmonale (see Pulmonary Hypertension, [[Pulmonary Hypertension]])

Treatment

  • Treat Underlying Disease
  • Ventilation
    • Rocking Bed
    • CPAP/BiPAP
    • Ventilator
  • Phrenic Nerve Pacing
    • Not usually useful (due to injured phrenic nerve/ pacing beyond site of injury is usually not possible due to atrophy of nerve)
    • Direct pacing of muscle requires excessively high thresholds

Prognosis

  • Spontaneous recovery (may take up to 2 years): may occur if a progressive generalized neuropathic process is not present