Unilateral Diaphragmatic Paralysis Presumed Secondary to Parsonage-Turner Syndrome Presenting as Orthopnea.

Unilateral diaphragmatic paralysis is an uncommon cause of dyspnea and orthopnea and may be overlooked when symptoms are attributed to more common cardiopulmonary conditions. This is particularly relevant in patients with underlying chronic obstructive pulmonary disease, where progressive breathlessness may initially be attributed to worsening obstructive lung disease. Parsonage-Turner syndrome, also known as neuralgic amyotrophy, is a rare neuropathic disorder that typically presents with acute shoulder or upper limb pain followed by weakness. Phrenic nerve involvement is uncommon but can result in diaphragmatic dysfunction and positional breathlessness. We present the case of a 56-year-old woman with a background of chronic obstructive pulmonary disease who developed progressive dyspnea and orthopnea over several months. She had initially been treated for worsening chronic obstructive pulmonary disease and was later referred for cardiac assessment, which did not identify a cardiac cause. Chest imaging demonstrated elevation of the right hemidiaphragm, prompting respiratory review. Retrospective history-taking revealed that her symptoms followed a flu-like illness associated with right arm and lower chest pain, reduced grip strength, and difficulty opening lids. Examination demonstrated weakness of right thumb abduction and adduction. Diaphragm ultrasound was reported as showing complete paralysis of the right hemidiaphragm, and further cross-sectional imaging excluded alternative structural causes. Positional spirometry demonstrated a marked reduction in lung volumes when supine, supporting diaphragmatic dysfunction. Electromyography and nerve conduction studies were performed late, approximately 10 months after symptom onset, and were non-diagnostic. A clinically supported diagnosis of unilateral diaphragmatic paralysis presumed secondary to Parsonage-Turner syndrome with phrenic nerve involvement was made. Management focused on diaphragmatic physiotherapy, breathing exercises, and optimisation of chronic obstructive pulmonary disease treatment, with subsequent symptomatic and spirometric improvement. This case highlights the importance of considering diaphragmatic paralysis in patients with persistent unexplained orthopnea, particularly when cardiac investigations are non-diagnostic and neurological symptoms are present.