Histologic changes: Scattered throughout the infiltrate are these collections. What are they, and what type of cell is marked with the asterisk? Answer

Given the history, CT findings, and histology, what is the best diagnosis? Answer

A

B. For comparison, these granulomas are from a patient with sarcoidosis. They, too, are non-necrotizing and composed of epithelioid histiocytes, multinucleated giant cells, and lymphocytes, but in this case the lymphocytes are predominantly of the T-helper type, rather than the T-suppressor/cytotoxic type of hypersensitivity pneumonia (HP). The granuloma of sarcoidosis is usually more well-defined and not surrounded by as many lymphocytes as the granuloma of HP. Usually, but not always, the granulomas of sarcoidosis are larger than those of HP. In this example, the granulomas are undergoing fibrosis, which does not happen in HP.

B

Clinical summaryImage 4

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Answer: This is a non-necrotizing granuloma that is composed of epithelioid cells, multinucleated giant cells, and lymphocytes. The asterisk marks a Langhans' giant cell with peripherally-oriented nuclei. The epithelioid cells are activated macrophages that have a secretory function rather than a phagocytic one. Metabolic products include calcium salts that can crystallize to form birefringent crystals, which must not be mistaken for foreign bodies.

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Answer: The respiratory problems that developed while the patient was keeping pets, the patchy ground-glass opacities and micronodules on HRCT, the evidence of air trapping on expiratory CT, the bronchiolar and patchy, alveolar lymphoid infiltrates and non-necrotizing granulomas are consistent with the diagnosis of hypersensitivity pneumonia. In this case no precipitating antibodies to common antigens, including pigeon antigens, were identified. After the animals were removed, her symptoms diminished without steroid treatment, and she has continued treatment with combination antiretroviral agents.

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