Images in Haematology: A Rare Visualisation of Histoplasma Capsulatum in Peripheral Blood Smear and Bone Marrow Aspirate

A 70-year-old Indian female with a history of Chronic Obstructive Pulmonary Disease (COPD), using an Asthalin inhaler (Salbutamol, 100 mcg/puff) (2 puffs as needed), presented with a low-grade fever, dry cough and mild hepatosplenomegaly. For fever, she was prescribed paracetamol 650 mg as needed, and for cough, benzydamine hydrochloride syrup 10 mL orally. Importantly, the patient had not received any corticosteroids. General examination revealed weight loss. On respiratory system examination, mild wheeze was noted bilaterally. Abdominal examination also demonstrated mild hepatosplenomegaly. Cardiovascular and central nervous system examinations were normal and revealed no significant abnormalities. Initial laboratory investigations showed haemoglobin 10 g/dL, total leukocyte count 7800/cu mm, platelet count 46000/ cu mm, C-Reactive Protein (CRP) 36.4 mg/L, serum creatinine 1.1 mg/dL, total bilirubin 1.50 mg/dL (direct bilirubin 0.96 mg/dL), total protein 5.6 g/dL, and serum albumin 2.4 g/dL. Liver enzymes were also normal {Serum Glutamate Pyruvate Transaminase (SGPT 31 IU/L)}. The patient thus demonstrated isolated thrombocytopenia with mild anaemia and normal leukocyte count. Biochemistry showed hypoproteinaemia and hypoalbuminaemia, a slight rise in bilirubin, and increased C-Reactive Protein (CRP). Peripheral blood and buffy coat smears demonstrated intracellular and extracellular forms of Histoplasma capsulatum as shown in [Table/ Fig-1]. On the peripheral smear, small (2-5 μm) oval yeast forms with narrow-based budding and a surrounding clear halo were observed, which indicated a possible capsule-like structure. The presence of intracellular organisms within neutrophils was noted, which was thus consistent with disseminated infection, whereas the extracellular clusters among erythrocytes showed uniform budding yeasts with eccentric acorn-like nuclei. Bone marrow aspirate and special stains {Periodic Acid–Schiff (PAS), Gomori Methenamine Silver (GMS)} confirmed the presence of H. capsulatum as shown in [Table/Fig-2]. The bone marrow aspirate showed small (2-5 μm) oval yeast forms with narrow-based budding, present as both intracellular and extracellular clusters, with a clear halo, which indicated the presence of a capsule. The PAS stain showed thick, magenta-stained capsules surrounding the yeasts, thus confirming the polysaccharide-rich cell wall. As a confirmation regarding the presence of fungal elements, GMS staining revealed fungal cell walls as black structures against a pale green background.