A 30-year-old man undergoes a lung biopsy, which shows multiple nodular lesions consisting of large epithelioid cells surrounded by lymphocytes and fibroblasts. There is an area of necrosis in the center of some nodules. Numerous acid-fast bacilli are demonstrated by Ziehl-Neelsen staining within the cytoplasm of epithelioid cells. Silver stains for fungi are negative. Which of the following is the MOST likely condition that predisposed the patient to this pulmonary disease?
Correct Answer: Acquired immunodeficiency syndrome (AIDS)
Description: The lesion shown is a necrotizing granuloma developing as a result of infection by acid-fast bacilli (most likely mycobacteria). Granulomatous inflammation is a specialized form of chronic inflammation, which begins with the uptake of foreign antigens by macrophages. These cells process and present the antigen to helper T lymphocytes, which in turn activate macrophages by interferon-g secretion. Granulomas may be due to infectious and noninfectious causes. Usually, infectious granulomas are necrotizing and non-infectious granulomas are non-necrotizing, but there are many exceptions to this rule. Among the infectious causes, mycobacterial infections are of the utmost impoance, especially in patients with AIDS. Fungi may also cause granulomas, which may be of the necrotizing or non-necrotizing type. By definition, however, caseating necrosis is pathognomonic of mycobacterial infection.Also know:Common variable immunodeficiency is one of the most common forms of congenital immune deficiency syndrome. It is due to inability of lymphocytes to mature into plasma cells. Consequently, levels of immunoglobulins are depressed, and patients suffer from depressed humoral immunity. Cell-mediated immunity (on which granuloma formation is largely dependent) is intact. Cystic fibrosis predisposes to recurrent bronchopneumonia and development of bronchiectasis. Depressed level of consciousness predisposes to aspiration of gastric contents and development of aspiration pneumonia. Sheets of macrophages are often observed, but not necrotizing granulomas (unless there are additional predisposing conditions, such as AIDS). Ref: Chandrasoma P., Taylor C.R. (1998). Chapter 7. Deficiencies of the Host Response. In P. Chandrasoma, C.R. Taylor (Eds), Concise Pathology, 3e.
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