<prompt> A 19-year-old man presents with coughing up blood and decreased urine output. On examination, he has normal air entry, and heart sounds. There is no skin rash or lymph nodes and his abdomen is normal. CXR reveals patchy infiltrates in both lower lobes and his creatinine is elevated. Urinalysis is positive for red cells and protein. A renal biopsy reveals autoantibodies to basement membranes. Which of the following is the most likely diagnosis?thyroiditismyasthenia gravisGoodpastures syndromethrombocytopenia  <response>: Autoantibodies can be demonstrated by immunofluorescence or electron microscopy on the basement membranes of glomeruli and alveoli in Goodpastures syndrome. The disease is most common in young men but can strike at any age. The hemoptysis can be minimal or massive. The course of the hemoptysis is variable, but renal involvement is often progressive. Current therapy includes intensive plasma exchange, cytotoxic agents, and glucocorticoids. Other causes of lung-renal syndromes such as various vasculitides, Wegeners granulomatosis, mixed essential cryoglobulinemia, Henoch-Schonlein purpura, and systemic lupus erythematosus SLE are not characterized by antibodies to basement membranes. 