CHIEF COMPLAINT A 12-year-old girl with a history of mild persistent asthma came to the emergency department with a 24-hour history of respiratory distress. She reported the sudden onset of shortness of breath accompanied by right shoulder pain and rightsided pleuritic chest pain. She was unable to lie flat. She was in her usual state of health until 1 month earlier when she began to take frequent naps after school and to have difficulty climbing stairs because of easy fatigability. These symptoms were all attributed to her asthma. There was a 1-week history of mild nonproductive cough with wheeze. She denied fever or other systemic symptoms.