Wild-Type Transthyretin Amyloidosis Complicated by Alveolar Hypoventilation due to Diaphragmatic Dysfunction

We report a case of wild-type transthyretin amyloidosis (ATTRwt) in a 91-year-old female who developed alveolar hypoventilation despite improvement in heart failure. The patient presented with dyspnea and lower extremity edema, and was diagnosed with heart failure. ⁹⁹ᵐTc-pyrophosphate scintigraphy scan showed cardiac uptake consistent with transthyretin amyloidosis, and genetic testing confirmed wild-type disease. While cardiac symptoms improved with treatment, hypercapnia persisted, prompting pulmonology consultation. Chest radiographs and dynamic magnetic resonance imaging during inspiration and expiration revealed impaired diaphragmatic movement. A chest computed tomography scan showed no significant abnormal findings in the lung fields. Pulmonary function tests revealed mixed ventilatory impairment with preserved total lung capacity but increased residual volume. Maximum inspiratory and expiratory pressures were significantly decreased. Ultrasound evaluation revealed diaphragmatic weakness with minimal thickening during inspiration. Phrenic nerve conduction studies were normal. This case represents the first report of alveolar hypoventilation due to diaphragmatic dysfunction in ATTRwt.