Radiation-Induced Unilateral Diaphragmatic Paralysis Following Breast and Nodal Radiotherapy.

Unilateral diaphragmatic paralysis is a rare but important complication of thoracic radiotherapy, typically resulting from unintended injury to the phrenic nerve when it lies within or adjacent to the radiation field. While radiation-induced pulmonary toxicities such as pneumonitis and fibrosis are well documented, neurological complications like phrenic neuropathy remain underrecognized and likely underreported, despite their potential to cause significant respiratory dysfunction. We present the case of a 52-year-old woman with triple-negative breast cancer who developed progressive dyspnoea and orthopnoea 2 months after completing adjuvant breast and nodal radiotherapy. Imaging revealed new elevation of the right hemidiaphragm, and pulmonary function tests showed a restrictive ventilatory pattern. A fluoroscopic sniff test confirmed paradoxical motion of the right hemidiaphragm, consistent with unilateral diaphragmatic paralysis. The patient's symptoms improved with nocturnal non-invasive ventilation. LEARNING POINTS: Clinicians should be aware that thoracic radiotherapy, particularly for breast cancer involving regional nodal irradiation can inadvertently damage the phrenic nerve due to its anatomical proximity to the treatment field.New-onset dyspnoea or orthopnoea following radiation therapy should prompt evaluation with chest imaging, pulmonary function testing, and a fluoroscopic sniff test to assess diaphragmatic dysfunction.Although management of diaphragmatic paralysis is primarily supportive, interventions such as non-invasive ventilation can alleviate symptoms. Timely diagnosis is crucial, as prolonged dysfunction may lead to persistent morbidity.