Chapter 34: Pathology of Lung Infections

Chapter 34. Pathology of Lung Infections

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?

a. Gram-negative bacilli

b. Gram-negative coccobacilli

c. Gram-positive cocci in pairs

d. Gram-positive cocci in grapelike clusters

e. Acid-fast bacilli

The most correct answer is c, gram-positive cocci in pairs.

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.

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?

a. Primary tuberculosis at present

b. Primary tuberculosis in the past

c. Secondary (reactivation) tuberculosis

d. Miliary tuberculosis

The most correct answer is b, primary tuberculosis in the past.

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 ...