Phrenic Neuropathy

Etiology

Alcoholic Neuropathy (see Alcoholic Neuropathy)
Buckthorn Berry Intoxication (see Buckthorn Berry Intoxication)
Diphtheria (see Diphtheria)
Lyme Disease (see Lyme Disease)
Paralytic-Neurotoxic Shellfish Poisoning (see Paralytic-Neurotoxic Shellfish Poisoning)
- Descending paralysis (similar to botulism and in contrast to ascending paralysis seen in GBS and tick paralysis)
Poisonous Lizard Bite (see Poisonous Lizard Bite)
Rabies (see Rabies)
- Ascending paralysis may mimic that of GBS
Widow Spider Bite (see Widow Spider Bite)

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

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)

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

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]])

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

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