16 Jun Histoplasmosis
Aspiratefrom a lymph node from a6.5-year-old, neutered, male cat.The lymph node had been mildly enlargedfor months and had recently started growing.The image consists a few macrophages, three small lymphocytesand twoneutrophils. Several of the macrophages contain 2-4 μm, oval yeast (Histoplasma capsulatum) with a thin, clear, cellwall,and an eccentric, occasionally crescent-shaped purple nucleus,that exhibits narrow-based budding.
H. capsulatumis a dimorphic fungus that tends to grow in soil or material rich in bird or batexcrement, such as chickencoops and caves, although exposure to this environment may not be present in the history. Disseminated disease is notuncommon in cats, including lymphadenopathy (present in this case). The organism may also be observed in circulatingneutrophils and monocytes,albeit in rare cases.
When preparing slides from lymph nodes, it is important to use a gentle blood smear technique to spread the aspiratedmaterial on the slide. Lymphocytes are fragile cells and easily disruptedif too much pressure is applied during samplepreparation, resulting in a non-diagnostic sample.