Case Diagnosis: Acute Hypoxic Respiratory Failure secondary to Bilateral Phrenic Mononeuropathy with Axonal Injury
Case Description: Patient with a 6 month history of progressive weakness and neurogenic claudication was admitted to an intensive care unit (ICU) due to central cord syndrome and cervical myelopathy, with bilateral upper extremity strength of 1/5 and bilateral lower extremity strength of 4/5 on manual muscle testing. Cervical spine magnetic resonance imaging (MRI) demonstrated posterior disc osteophyte complexes at C3-C4 with severe ligamentum flavum hypertrophy, degenerative facet disease, and spinal cord compression. The patient underwent C3-C4 anterior cervical discectomy allograft/autograft placement. Post-operatively he developed acute hypoxic respiratory failure requiring ventilation. Physiatry was consulted to perform electrodiagnostic studies (EDXs). EDXs confirmed evidence of moderate bilateral phrenic mononeuropathy. Nerve conduction studies of the bilateral phrenic nerves revealed severely prolonged distal onset latency and severely reduced amplitudes, consistent with axonal injury.
Discussions: Cervical spinal cord injuries have the propensity to lead to restrictive respiratory changes secondary to thoracic column degeneration, leading to accessory muscle weakness. Phrenic nerve involvement seen in higher cervical cord injuries can also lead to respiratory compromise due to denervation of the diaphragm. EDXs may be used to evaluate the function of the phrenic nerve in patients that are ventilator dependent in the intensive care unit. Findings of axonotmesis in this case demonstrates an intact epineurium indicating the opportunity for neuronal regeneration. This information helps prognosticate the possibility of weaning from ventilator support in the near future.
Conclusions: Our physiatry team was consulted to perform a procedure on a critically ill patient in the ICU to help provide prognosis for respiratory failure. EDXs are helpful in diagnosing the severity of phrenic nerve injury. This delineates the degree of injury and helps to determine prognosis such as ventilator dependence or candidacy for diaphragmatic pacer in critically ill spinal cord injury patients.