BACKGROUND: Histoplasmosis results from the inhalation of spores from the fungus, Histoplasma capsulatum. A case is presented of pulmonary histoplasmosis associated with altered mental state and hypercalcemia following allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia (AML).

CASE REPORT: A 75-year-old man with a five-day history of AML treated with allogeneic hematopoietic stem cell transplantation, presented with weakness, fatigue, and slow mentation. Computed tomography (CT) of the brain was unremarkable. Laboratory investigations showed serum albumin of 2.9 g/dL, calcium of 11.6 mg/dL, ionized calcium of 1.55 mmol/L, parathyroid hormone (PTH) <6.3 pg/mL, and 25-hydroxy vitamin D of 14.4 ng/mL. Treatment began with intravenous cefepime 1 gm bid, normal saline, and the bisphosphonate, pamidronate, administered as a single dose. Three days later, his clinical status declined. He developed a dry productive cough, his oxygen saturation (O₂ Sat) was 90%, and his mental status worsened. Chest CT showed diffuse bilateral lung infiltrates with ground glass opacities. Bronchioalveolar lavage and transbronchial biopsy were negative for Pneumocystis jiroveci pneumonia (PJP). The CMV rival load was 195 IU/mL. Urinalysis for Histoplasma antigen and the Fungitell® assay were positive. Treatment commenced with intravenous voriconazole (250 mg, bid) and ganciclovir (5 mg/kg, bid). A left lower lobe transbronchial lung biopsy was positive for Histoplasma capsulatum and negative for CMV.

CONCLUSIONS: This case report has highlighted the need for awareness of the diagnosis of histoplasmosis in patients with allogeneic hematopoietic stem cell transplantation who present with an altered mental state in the setting of hypercalcemia.

Keywords: Histoplasmosis, Hypercalcemia, Stem Cell Transplantation, Histoplasma, Immunocompromised Host, Leukemia, Myeloid, Acute, Lung Diseases, Fungal, Mental Disorders