A78-12 Breathless Weeks After Radiation: An Unexpected Phrenic Nerve Injury

Introduction Head and neck radiotherapy can incidentally expose the phrenic nerve (C3-C5 along the anterior scalene), especially when lower cervical or supraclavicular nodal regions are included. Radiation-associated phrenic nerve injury is rare and typically presents months to years after treatment due to delayed fibrosis and microvascular injury. We describe an unusually early presentation occurring within weeks of radiation therapy for laryngeal carcinoma. Case Description A 49-year-old man developed progressive dyspnea and orthopnea for 2-3 weeks, beginning shortly after completing concurrent cisplatin-based chemoradiation for supraglottic and glottic squamous cell carcinoma 4 weeks earlier. Medical history included Heart Failure with preserved ejection fraction, persistent atrial fibrillation on digoxin and rivaroxaban, asthma, untreated obstructive sleep apnea, type 2 diabetes, and opioid use disorder managed with buprenorphine/naloxone. At an outside hospital, he was treated empirically with corticosteroids and doxycycline for presumed pneumonia after chest radiography showed an elevated right hemidiaphragm. Upon presentation, he was afebrile, euvolemic, and oxygenating well on room air. Examination revealed oral thrush and decreased breath sounds at the right lung base without peripheral edema or jugular venous distension. Laboratory studies showed normal procalcitonin and C-reactive protein, baseline BNP, and no leukocytosis. Chest CT confirmed right hemidiaphragm elevation with mild basilar atelectasis without consolidation, pleural effusion, or tumor recurrence. Fluoroscopic sniff testing showed absent right diaphragmatic motion, and pulmonary function testing revealed a restrictive pattern. Neck imaging ruled out structural phrenic nerve compression. Given the close temporal association with radiotherapy and exclusion of other causes, acute radiation-associated phrenic nerve injury was diagnosed. Pulmonary and thoracic surgery teams recommended conservative management. He was treated with fluconazole for oral candidiasis and underwent pulmonary rehabilitation, including incentive spirometry, oscillatory positive expiratory pressure therapy, and chest physiotherapy. A brief diuretic trial yielded no improvement. He remained clinically stable and was discharged with multidisciplinary follow-up. Discussion Although uncommon and usually delayed, radiation-induced phrenic nerve injury can occur shortly after treatment. Acute presentation likely reflects inflammatory neuritis. Diagnosis relies on dynamic imaging, including sniff testing or bedside ultrasound, and correlation with clinical findings. Management is supportive, emphasizing respiratory muscle training, pulmonary hygiene, and optimization of comorbid heart failure and sleep apnea. Early recognition, conservative management, and multidisciplinary follow-up can optimize recovery and prevent inappropriate interventions.