Etiology
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