Snapshot A 32-year-old man with HIV presents to the clinic for increasing shortness of breath and a nonproductive cough for the past few days. He denies having any hemoptysis. On physical exam, he is found to be tachypneic and tachycardic, with diffuse crackles and rhonchi bilaterally. Laboratory exam reveals a lactic dehydrogenase of 300 U/L. A chest radiograph shows diffuse patchy infiltrates bilaterally. Empiric antibiotics are started immediately while a bronchoalveolar lavage is scheduled. Introduction Classification Pneumocystis jirovecii pneumonia (previously Pneumocysis carinii pneumonia) a yeast-like fungus airborne transmission Epidemiology incidence decreased since the use of prophylaxis in vulnerable populations more common in developing countries risk factors immunodeficiency HIV malignancy smoking Pathogenesis when both humoral and cellular immunity are suppressed, Pneumocystis attaches to the alveoli activated alveolar macrophages without CD4+ cells are not able to fight the organisms this causes hypoxemia with ↑ alveolar-arterial oxygen gradient and respiratory alkalosis Associated conditions HIV Prevention smoking cessation prophylaxis with medication trimethoprim-sulfamethoxazole (TMP-SMX) dapsone and pyrimethamine Prognosis mortality is 10-20% Presentation Symptoms most are asymptomatic in patients with normal immune systems causes interstitial pneumonia in patients with immunosuppression progressive exertional shortness of breath chest pain nonproductive cough fever and chills hemoptysis is rare Physical exam tachypnea, tachycardia, and fever mild crackles and rhonchi in the bilateral lung fields Imaging Chest radiography indication all patients findings bilateral and diffuse infiltrates Computed tomography (CT) of the chest indication if chest radiograph is unclear findings bilateral and diffuse patchy ground-glass opacities pneumatoceles Studies Labs ↑ lactic dehydrogenase Pulmonary function tests ↓ diffusion capacity of carbon monoxide < 75% predicted high sensitivity Histology methenamine silver, Diff-Quik, or Wright stain of lung tissue disc-shaped yeast Making the diagnosis based on lung biopsy or lavage and histology lung tissue histology is needed for a definitive diagnosis Differential Cytomegalovirus (CMV) pneumonia distinguishing factors patients also present with pharyngitis as well as lymphadenopathy and splenomegaly in HIV patients, CMV also involves the gastrointestinal tract Tuberculosis distinguishing factor often presents with hemoptysis Treatment Management approach treatment may be initiated prior to definitive diagnosis Medical trimethoprim-sulfamethoxazole (TMP-SMX) indications first-line therapy prophylaxis when CD4+ count < 200 cells/mm3 corticosteroids indications in HIV patients with severe cases (arterial-alveolar oxygen gradient > 35 mmHg or PaO2 < 70 mmHg) always given alongside antibiotics pentamidine indication second-line therapy if resistant to TMP-SMX atovaquone indication second-line therapy if resistant to TMP-SMX dapsone and pyrimethamine indication prophylaxis when CD4+ count < 200 cells/mm3 Complications Acute respiratory distress syndrome