An Uncommon Cause of Dyspnea: Parsonage-Turner Syndrome With Bilateral Phrenic Nerve Involvement.

Parsonage-Turner syndrome, also called neuralgic amyotrophy, typically affects the brachial plexus, while involvement of the phrenic nerve is far less commonly documented. When present, it can compromise diaphragmatic function, producing breathlessness with activity, orthopnea, or, in more advanced presentations, respiratory failure. These features are easily mistaken for other cardiac or pulmonary conditions, which often delays correct diagnosis. A 51-year-old woman presented with a five-month course of worsening breathlessness on exertion and inability to breathe comfortably while supine. Cardiac work-up did not identify an underlying cause. Radiological assessment of the chest showed abnormal elevation of the right side of the diaphragm, with no associated pleural or lung tissue findings. Her history, obtained retrospectively, included an earlier episode of severe pain affecting the neck and left shoulder region, linked temporally to a stressful period. Ultrasound examination showed reduced diaphragmatic movement on both sides. Lung function testing showed a restrictive defect, and vital capacity fell markedly upon lying down compared with sitting. Electrophysiological testing identified a bilateral brachial plexopathy pattern, with phrenic nerve dysfunction predominating on the left side and additional denervation changes affecting other nerve territories, in keeping with neuralgic amyotrophy. She responded well to a combined respiratory rehabilitation approach incorporating ventilatory assistance, with subsequent improvement in her symptoms and lung volumes. While diaphragmatic involvement occurs infrequently in neuralgic amyotrophy, it carries meaningful clinical implications and merits consideration whenever dyspnea or orthopnea cannot be explained, especially after cardiac disease is excluded and imaging identifies a raised hemidiaphragm on either or both sides. The combination of a significant postural fall in vital capacity, suggestive diaphragmatic ultrasound findings, and electrophysiological data (nerve conduction studies/electromyography) supports the diagnosis. Prompt clinical suspicion of this etiology, when relevant, allows for faster initiation of respiratory rehabilitation and ventilatory support, if required.