INTRODUCTION: Although mediastinal masses are not uncommon, progressive respiratory failure due to tumor induced phrenic nerve injury has not been well described. This case serves as a model in diagnosing bilateral diaphragmatic paralysis in the critical care setting.
CASE PRESENTATION: A 37-year-old woman with end stage renal disease developed progressive orthopnea over a two month period. She was found to have a large mediastinal mass on radiographs. A CT scan showed an extensive 7 x 9 centimeter mass occupying her mediastinum and surrounding the airways (see figure). She was admitted for mediastinoscopic biopsy and pathology revealed malignant lymphoma. During her recovery she developed respiratory distress and orthopnea. On day five post-op she required re-intubation and was transferred to the ICU. A bronchoscopic airway exam showed no extrinsic compression or endobronchial lesions. Again she was extubated, however rapidly developed accessory muscle use, displayed paradoxical respirations and became somnolent with significant hypercapnea. She was re-intubated and immediately recovered from the episode. The possibility of diaphragm paralysis was entertained. Esophageal and gastric pressure measurements were obtained using balloon tipped catheters while the patient remained intubated on a spontaneous mode of ventilation. Negative waveform deflections during inspiration in both the esophageal and gastric pressure monitor tracings resulted in a diaphragm pressure of zero by the equation (P diaphragm = P gastric - P esophageal). This finding was consistent with the diagnosis of bilateral diaphragm paralysis1. A nerve conduction study and electromyogram of the phrenic nerves confirmed bilateral phrenic neuropathy with denervation of the diaphragm.
DISCUSSIONS: The location of the phrenic nerves in the mediastinum leaves them susceptible to damage from masses, trauma, and iatrogenic injury. Neuropathy from compressive conditions has been described in the literature; hematomas forming after anticoagulation and thrombolytics, compression from left atrial enlargement, and intra-thoracic thyroid goiters. Diabetic neuropathy affecting the phrenic nerve has also been reported. Peripheral neuropathies have been associated with lymphomas. Pathogenesis of lymphoma-associated neuropathy has been elucidated and includes direct invasion and infiltration of nerve bundles by lymphoma cells, metabolic derangements, vascular impairment, infection, and immunologic mechanisms including paraneoplastic neuropathy. Bilateral phrenic neuropathy may present as dyspnea and tachypnea at rest, with the symptoms worsening in the supine position. Use of accessory muscles and paradoxical respirations are the primary clinical sign of bilateral phrenic neuropathy. Diagnostic evaluation includes chest radiography, fluoroscopy, pulmonary function testing, esophageal and gastric manometry, and EMG/nerve conduction studies.
CONCLUSION: Evaluations of diaphragm function in the critical care setting can be difficult, especially with mechanically ventilated patients. We used esophageal and gastric balloon catheters to evaluate pressure waveform tracings while the patient remained on the ventilator. Although an unfortunate situation, this case serves as a reminder to consider diaphragm dysfunction when formulating a differential diagnosis in acute or progressive respiratory failure. In cases of diaphragm dysfunction, knowledge of the defect prior to extubation can allow the critical care team to anticipate the needs of the patient and plan for successful weaning.
DISCLOSURE: Anthony Zachria, None.