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A 75-year-old man with diabetes mellitus, chronic obstructive pulmonary disease, and congestive heart failure presents with malaise, fever, and a productive cough. A chest radiograph shows well-circumscribed radiopacity of the entire left lower lobe. Gram stain of sputum is most likely to show which of the following?
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b. Gram-negative coccobacilli
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c. Gram-positive cocci in pairs
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d. Gram-positive cocci in grapelike clusters
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The most correct answer is c, gram-positive cocci in pairs.
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The patient has lobar pneumonia. Streptococcus pneumoniae (Pneumococcus) is the cause of more than 90% of cases of lobar pneumonia, the patient has several risk factors for pneumococcal pneumonia, and the morphology of S. pneumoniae is gram-positive cocci in pairs (answer c). Klebsiella pneumoniae can cause lobar pneumonia less commonly, and its morphology is gram-negative bacilli (answer a). Haemophilus influenzae and Moraxella catarrhalis are both gram-negative coccobacilli (answer b) but typically cause bronchopneumonia. Staphylococcus aureus generally causes bronchopneumonia, although it can cause lobar pneumonia less commonly than Pneumococcus; its morphology is gram-positive cocci in clusters (answer d). Acid-fast bacilli (answer e) cause granulomatous inflammation (eg, tuberculosis) and would not be visible on a gram stain.
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A 40-year-old man presents to the emergency room, having fallen down some steps and sustained traumatic injury to his back. A chest radiograph is obtained and is negative for bone fractures; however, there is a focus of calcification in what appears to be the lower portion of the left upper lobe and a second focus of calcification in the left hilum. Which of the following is most likely the correct diagnosis?
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a. Primary tuberculosis at present
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b. Primary tuberculosis in the past
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c. Secondary (reactivation) tuberculosis
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The most correct answer is b, primary tuberculosis in the past.
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The locations of the calcifications are characteristic of a Ghon complex, typical of primary tuberculosis. Calcification occurs with healing and would not be present if the patient currently had primary tuberculosis (answer a). The lesions of secondary (reactivation) tuberculosis (answer c) are typically within 2 cm of the pleura of the lung apex. The lesions of miliary tuberculosis (answer d) are widely disseminated throughout the lungs and small enough not likely to be visible on a chest radiograph. While the patient may have miliary TB (answer d), statistically speaking, it is more likely that he does not.
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A child being treated for leukemia develops a pulmonary infarct and subsequently dies of a stroke. At autopsy, the infarct is seen to be associated with a thrombus. Histologically, the infarct is infiltrated by neutrophils, and the thrombus contains hyphae that are 5-10 μm wide and have easily identified septa. Which of the following is the best diagnosis?
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The most correct answer is a, aspergillosis.
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Aspergillus species are angioinvasive and typically cause thrombosis and infarction with subsequent suppuration. Mucormycosis (answer b) clinically mimics aspergillosis; however, the Zygomycetes hyphae are only sparsely septate. The patient is at risk for candidiasis (answer c), but Candida morphology is budding yeast with pseudohyphae. The causative organisms of blastomycosis (answer d) and histoplasmosis (answer e) are yeasts at body temperature; hyphal forms of these microorganisms would only be expected at temperatures lower than body temperature as usually found in soils.