A 62-year-old man comes to the physician because of recent weight loss, cough, and occasional hemoptysis. His past medical history is significant for poorly controlled diabetes mellitus and chronic obstructive pulmonary disease treated with bronchodilators and oral corticosteroids. Chest x-ray shows pulmonary infiltrates and an area of cavitation in the right upper lobe. Sputum microscopy shows acid-fast bacilli. Which of the following is the most accurate statement concerning this patient's pulmonary infection?

Question

A 62-year-old man comes to the physician because of recent weight loss, cough, and occasional hemoptysis.  His past medical history is significant for poorly controlled diabetes mellitus and chronic obstructive pulmonary disease treated with bronchodilators and oral corticosteroids.  Chest x-ray shows pulmonary infiltrates and an area of cavitation in the right upper lobe.  Sputum microscopy shows acid-fast bacilli.  Which of the following is the most accurate statement concerning this patient's pulmonary infection?

Quizplus · Accepted Answer

11ec160b_3a21_882c_9249_f523a08c09e0_MD0001_00 This patient's symptoms (cough, hemoptysis, weight loss), acid-fast bacilli on sputum culture, and upper lobe cavitary lesion are suggestive of secondary (reactivation) tuberculosis. His advanced age, multiple comorbidities, and partial immune suppression secondary to chronic oral corticosteroid use also place him at risk for reactivation disease. Primary tuberculosis infection occurs following inhalation of aerosolized Mycobacterium tuberculosis. The organisms are deposited in the lower lungs and phagocytosed by alveolar macrophages, where they proliferate until the macrophages are activated by T_H1 lymphocytes. The infection can be subsequently eliminated if the area of involvement is small enough. However, larger regions of caseating necrosis become walled off, allowing M tuberculosis to survive in a dormant state without causing disease or symptoms. Later in life (usually following immunosuppression by drugs or HIV) the bacteria can reactivate and establish infection in the upper lungs (particularly the apex). The predilection for upper lung regions may be related to decreased lymphatic flow or increased oxygen tension. The organisms multiply in the apices, causing caseous and liquefactive necrosis and extensive cavitary disease. Erosion into the pulmonary vessels can result in severe hemoptysis. Hematogenous dissemination may also occur, causing miliary or extrapulmonary (eg, Potts disease, tuberculous meningitis) tuberculosis. (Choice A) Primary tuberculosis infection often begins as a focal lesion in the mid-to-lower lungs (Ghon focus). M tuberculosis then spreads lymphatically to the hilar lymph nodes, forming a Ghon complex. The organisms can remain dormant in a walled-off Ghon complex for many years before reactivating. Alternatively, the lesion may heal, forming a benign, calcified Ranke complex that is not associated with reactivation tuberculosis. (Choice B) A Ghon complex forms during primary tuberculosis infection and consists of a Ghon focus and hilar lymphadenopathy. This patient's upper lung involvement and cavitary lesion are more characteristic of secondary (reactivation) tuberculosis. Healing of this lesion would result in a persistent cavity that may become secondarily infected with Aspergillus flavus and form fungus balls. (Choice D) M tuberculosis is a facultative intracellular bacterium that can survive and multiply within macrophages; as a result, circulating antibodies cannot bind it to promote phagocytosis or complement-mediated killing. Therefore, humoral immunity plays no role in the control of M tuberculosis. (Choice E) A negative skin tuberculin test after M tuberculosis exposure suggests anergy against tuberculosis antigens and a weak cell-mediated immune response. This can occur in the setting of HIV, sarcoidosis, and other illnesses. Educational objective: Primary tuberculosis causes the formation of Ghon foci in the lower lungs. Secondary (reactivation) tuberculosis occurs in patients with prior tuberculosis infection that never cleared completely. Reactivation tuberculosis occurs most often in immunosuppressed patients and is characterized by apical cavitary lesions and hemoptysis.

A 62-Year-Old Man Comes to the Physician Because of Recent