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The patient was a 27-year-old HIV-positive Kenyan woman (current CD4+ T-cell count of 80/mm3) admitted to the hospital with fever, hypotension, and acute abdominal pain. She was diagnosed with gastroenteritis and, upon further evaluation, was found to be pancytopenic. Her CBC results were as follows: RBC: 2.6 × 1012/L; hemoglobin: 6.9 g/dL; hematocrit: 20%; mean corpuscular volume: 78 fL; platelets: 35 × 109/L; WBC: 2.6 × 109/mm3 with the following differential: neutrophils: 77%, lymphocytes: 14%, monocytes: 7%, eosinophils: 0%, basophils: 2% 1.

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Image 1. Examination of the bone marrow aspirate smear revealed numerous negatively-stained bacilli located both within the cytoplasm of macrophages (pseudo-Gaucher cells) and outside of cells (A and B, Leishman stain, 10003). Bacillli were positive with Ziehl-Neelsen stain (B inset, 10003), consistent with mycobacteria. The bone marrow trephine biopsy showed replacement of the normal marrow by aggregates of foamy macrophages (C, hematoxylin & eosin, 4003) containing numerous PAS-positive bacilli (D, 10003), consistent with atypical mycobacteria.

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She was diagnosed with HIV infection 1 year prior, at which time her CD4+ T-cell count was 167/mm3 (reference range: 380–1080/mm3). At that time, she was started on antiretroviral therapy with lamivudine, tenofovir and nevirapine, and was also empirically started on anti-mycobacterial therapy with rifampin, isoniazid, ethambutol, and pyrazinamide. The patient self-discontinued the anti-mycobacterial therapy several months before admission.

During the current admission, bone marrow trephine biopsy and aspiration were performed to evaluate her pancytopenia. Leishman stain showed decreased hematopoietic elements and scattered admixed macrophages with abundant striated cytoplasm (Pseudo-Gaucher cells) containing numerous negatively-stained bacilli (A). Bacilli were also present extracellularly (B) and were positive with Ziehl-Neelsen stain (B, inset), confirming the presence of mycobacteria. The bone marrow trephine biopsy demonstrated similar findings with aggregates of foamy macrophages replacing much of the hemopoietic marrow (C). Staining of paraffin sections showed intracellular bacilli positive for both Ziehl-Neelsen (not shown) and Periodic acid-Schiff (PAS) stains (D), consistent with atypical mycobacteria. No material was submitted for culture. The patient was restarted on anti-mycobacterial quadruple therapy, but expired on the 15th hospital day.

Pancytopenia in this case was likely due to disseminated mycobacterial infection leading to extensive marrow replacement by histiocytes filled with acid-fast bacilli. The finding of pseudo-Gaucher histiocytes containing negatively-stained bacilli on air-dried Romanowsky-stained smears should lead to the suspicion of possible mycobacterial infection and further diagnostic work-up with special stains [1, 2]. The large number of intracellular bacilli and their simultaneous positivity with both Ziehl-Neelsen and PAS stains on paraffin sections is characteristic of atypical mycobacteria [3].

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