Abstract Introduction Phrenic neuropathies (PN) are an important cause of dyspnea and hypercapnic respiratory failure. A crucial yet often overlooked symptom is dyspnea associated with water immersion activities. This symptom which is frequently documented in patients with PN, carries a serious risk of drowning and should serve as a key clinical clue for underlying diaphragmatic weakness. This report details a case of severe unilateral diaphragmatic paralysis, where immersion dyspnea served as the respiratory harbinger guiding the diagnosis in a competitive athlete. Case Description A 47-year-old male athlete training for an Ironman triathlon, presented with exercise-induced dyspnea, wheezing and orthopnea following a major bike accident involving left sided trauma (rib fractures, pneumothorax, left clavicle/scapula fracture). Notably he reported difficulty swimming or water immersion dyspnea even before the accident. Chest x-ray revealed an elevated right hemidiaphragm. Pulmonary Function Tests (PFTs) showed normal baseline spirometry and diffusing capacity but Maximal Inspiratory Pressure (MIP) was reduced (51 cmH2O), indicating neuromuscular weakness. Cardiopulmonary Exercise Testing (CPET) demonstrated supranormal exercise capacity (Peak VO2 4.13 L/min, 122% predicted, Peak Work Rate 385 W, 170% predicted) with reduced breathing reserve of 2.4%, arguably normal with the other supranormal exercise parameters in a highly conditioned athlete. Electromyography (EMG) and nerve conduction studies revealed an absent right phrenic motor response while diaphragmatic ultrasound confirmed severe right hemidiaphragm atrophy (thickness 0.05 cm; normal 0.15 cm) and a poor thickening ratio (0.5; normal 1.2). Discussion Immersion dyspnea should immediately raise suspicion for phrenic neuropathy (PN) even in otherwise healthy and athletic individuals. In a Mayo Clinic study of 535 PN patients, only 4% (22 of 535) reported dyspnea triggered specifically by water immersion underscoring the rarity of this symptom. For 36% (8 of 22) immersion dyspnea was the first respiratory symptom and in 4.5% (1 of 22) it was the only symptom. Notably 18% (4 of 22) experienced near-drowning incidents. The hydrostatic pressure exerted by water worsens the mechanical disadvantage caused by a paralyzed diaphragm making immersion dyspnea a vital diagnostic warning sign. Because of its rarity but serious risks patients with diaphragmatic paralysis should be advised to avoid immersion activities particularly diving. This abstract is funded by: nnone
Udyawar et al. (Fri,) studied this question.