Coexistence of Autoimmune Pulmonary Alveolar Proteinosis With Small Cell Lung Cancer in a Man Presenting With Acute Onset Respiratory Failure

A 60-year-old man was referred to our Respiratory Department with progressive dyspnea on exertion and productive cough over the past two months. High-resolution computed tomography showed diffuse ground glass opacities with superimposed interlobular and intralobular septal thickening mainly in the middle and lower lobes, compatible with crazy paving pattern. Serology tests revealed positive antibody transcriptional intermediary factor-gamma 1 (TIF-1 gamma) in myositis panel and bronchoalveolar lavage revealed milky appearance and positive periodic acid-Schiff (PAS) stain. Pulmonary function tests showed moderate reduction in diffusing capacity for carbon monoxide. The working diagnosis of autoimmune pulmonary alveolar proteinosis was established by high detectable levels of anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) antibodies. Despite clinical and radiological improvement following treatment with whole lung lavage and inhaled sargramostim, patient's follow-up chest computed tomography revealed an enlargement of lower left paratracheal lymph node 4L. Endobronchial ultrasound bronchoscopy (EBUS) biopsy was compatible with small cell lung cancer (SCLC). Chemotherapeutic agents were promptly administrated, with no adverse events up until now.