A 34-year-old woman comes to the emergency department after noticing hemoptysis. Yesterday, the patient developed sudden-onset right-side chest pain and mild dyspnea while getting out of bed. For the last 4 days, she has had diarrhea as well as nausea and vomiting after eating in a new restaurant. The patient feels weak and thought her respiratory symptoms were due to being in bed and inactive. Her chest pain increases with deep breathing. Her other medical problems include HIV, heroin use, and a prior episode of cellulitis on the right arm. The patient's last CD4+ cell count 2 months ago was 350/mm³, and PPD at that time showed 2 mm of induration. She has a 15-pack-year smoking history. Temperature is 38.1 C (100.6 F), blood pressure is 110/70 mm Hg, and pulse is 112/min. Mucous membranes are dry. Breath sounds are diminished at the right lung base. Chest CT scan is shown below. Which of the following is the most likely diagnosis?

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11ec25c8_d200_fde8_bc81_534ed2dc2a70_MD0003_00 This patient's acute-onset pleuritic chest pain, hemoptysis, and tachycardia are suggestive of pulmonary embolism (PE). Hemoptysis is a result of pulmonary infarction. Low-grade fever and mild leukocytosis may also occur with PE. This patient's risk factors for venous thromboembolism include HIV and hemoconcentration due to dehydration in the setting of a recent gastrointestinal illness. Chest CT scan shows the characteristic wedge-shaped, pleural-based opacification that is likely to occur distal to a completely occluded pulmonary artery. Pulmonary infarct areas may also occasionally be seen on chest x-ray as a Hampton hump. An associated pleural effusion is often present on the same side as the infarct (ie, exudative effusion resulting from infarction-induced inflammation). On contrast-enhanced CT scan, the PE itself will appear as a pulmonary artery filling defect. filling defect (Choice A) Bacterial pneumonia presents with rapidly progressing chest pain, fevers, chills, cough, and dyspnea. Alveolar infiltrates may be seen on chest x-ray and CT scan but are not typically wedge-shaped as they follow bronchial rather than vascular distribution. Symptom onset is less likely to be as dramatic, and hemoptysis can occur but is uncommon. Bacterial pneumonia (Choice B) Lung cancer can cause cough, chest pain, dyspnea, and hemoptysis. However, symptoms are generally gradually progressive and imaging is more likely to show a discrete, spiculated mass rather than a peripheral, wedge-shaped lesion. Lung cancer (Choice C) Pneumocystis pneumonia is a common cause of dyspnea in patients with HIV/AIDS. However, it typically occurs in patients with CD4+ counts <200/mm³ and tends to be subacute in presentation. Imaging commonly shows a diffuse interstitial pattern. Pneumocystis pneumonia (Choice E) Although patients with HIV are at increased risk for pulmonary tuberculosis, this woman has a recent negative PPD, and the classic cavitary lesions are not seen (a false-negative PPD is unlikely in a patient with a CD4+ count of 350/mm³). In addition, pulmonary tuberculosis does not typically cause wedge-shaped lesions. pulmonary tuberculosis Educational objective: Pulmonary emboli classically present with sudden-onset pleuritic chest pain, cough, and dyspnea. Hemoptysis can occur as a result of pulmonary infarction. Chest CT scan showing a peripheral, wedge-shaped infarction is virtually pathognomonic for pulmonary embolism. References: Hematocrit and risk of venous thromboembolism in a general population. The Tromso study. (http://www.ncbi.nlm.nih.gov/pubmed/19833630) HIV-associated venous thromboembolism. (http://www.ncbi.nlm.nih.gov/pubmed/21869916)

A 34-Year-Old Woman Comes to the Emergency Department After Noticing