Severe Orthopnoea With Positional Paradoxical Breathing: A Response to Continuous Positive Airway Pressure

A 54-year-old man presented with an abrupt onset disabling orthopnoea preventing supine sleep for several months. Cardiopulmonary imaging excluded heart failure, pulmonary embolism, interstitial lung disease, and upper airway obstruction. Pulmonary function testing demonstrated restrictive ventilatory impairment, and arterial blood gas revealed hypercapnia suggestive of hypoventilation. Neurological examination in the supine position showed paradoxical breathing with inspiratory thoracic expansion and inward abdominal movement, raising suspicion of diaphragmatic dysfunction. Sleep study demonstrated moderate obstructive sleep apnoea with an apnoea-hypopnoea index (AHI) of 25 events per hour and disproportionate nocturnal hypoxaemia (mean oxygen saturation 84%, nadir 65%). Profound hypomagnesaemia with associated hypokalaemia was identified and corrected. Computed tomography (CT) imaging showed a subtle elevation of the left hemidiaphragm and documented marked dyspnoea during supine acquisition. Respiratory muscle testing demonstrated severe inspiratory muscle weakness consistent with ventilatory pump limitation. Nocturnal continuous positive airway pressure (CPAP) resulted in rapid symptomatic improvement, allowing recumbent sleep. Despite extensive in-hospital evaluation, the underlying cause of orthopnoea remained undetermined. Structured differential diagnosis of progressive diaphragmatic weakness included cervical myelopathy, phrenic neuropathy, neuromuscular junction disorder, and primary myopathy. Further outpatient evaluation was planned but could not be completed because of the patient's unexpected death from acute myocardial infarction one month after discharge. This case highlights the importance of considering ventilatory pump failure when orthopnoea is severe and cardiopulmonary evaluation is unrevealing.