Chronic Cough With Reduced Diffusing Capacity and Preserved-Ratio Impaired Spirometry in a Young Never-Smoker With Systemic Lupus Erythematosus: A Diagnostic Pitfall.

Chronic cough in patients with systemic lupus erythematosus can be difficult to evaluate, especially when initial testing is unrevealing. We report the case of a 33-year-old woman with long-standing systemic lupus erythematosus, biopsy-proven lupus nephritis, prior extrapulmonary pericardial tuberculosis, and no active or passive smoking exposure who developed a persistent dry cough for six months. She was initially treated for gastroesophageal reflux disease with pantoprazole, without meaningful relief. Chest radiography and swallowing assessment were normal. Initial pulmonary function testing in July 2023 was formally interpreted as moderate obstructive airways disease, mild parenchymal restriction, and a moderately severe diffusion defect, without a significant bronchodilator response. High-resolution volumetric computed tomography of the chest with dynamic airway assessment showed no emphysema, bronchiectasis, interstitial lung disease, tracheomalacia, or acute cardiopulmonary process. Her cough improved substantially after inhaled therapy with albuterol and budesonide/glycopyrrolate/formoterol fumarate. Repeat pulmonary function testing in October 2023 showed improved spirometric values, but the forced expiratory volume in one second/forced vital capacity ratio remained preserved, and hemoglobin-adjusted diffusing capacity remained reduced at 64% predicted. This case highlights a diagnostic pitfall: inhaler-responsive chronic cough and a pulmonary function report suggesting obstruction should be evaluated together with post-bronchodilator spirometry, diffusing capacity, imaging, and exposure history. In systemic lupus erythematosus, a persistent cough may be associated with clinically relevant pulmonary function abnormalities even when chest imaging is unrevealing.