B72-14 Acute Pulmonary Histoplasmosis Mimicking Malignancy in an Immunocompetent Woman

Abstract Introduction Histoplasmosis, caused by Histoplasma capsulatum, can range from asymptomatic infection to severe pulmonary or disseminated disease. We describe an immunocompetent woman who presented with persistent fevers and pulmonary findings initially concerning for malignancy. Case Presentation A 40-year-old woman with no significant past medical history presented with a two-week history of fever, chills, chest tightness, weakness, and fatigue. Her illness began with diffuse myalgias and low-grade fevers, later progressing to nightly fevers up to 102 °F, chills, and exertional dyspnea. She denied cough, sputum, or wheezing. Two home COVID-19 tests were negative, and a short course of oral steroids provided no relief.She reported frequent camping near Grand Rapids, Michigan, including a late August trip to Wilderness State Park near farmland. On admission, she was febrile to 102.5 °F and tachycardic at 116 bpm. A CT angiogram of the chest was negative for pulmonary embolism but showed a 9-mm pleural-based left upper lobe nodule and mildly enlarged left hilar lymph nodes up to 2 cm; lungs were otherwise clear (Figure 1A). Laboratory studies revealed mild transaminitis, anemia, and thrombocytopenia. Viral testing, autoimmune workup, and blood cultures were negative. She was started on ceftriaxone and azithromycin for presumed community-acquired pneumonia.By hospital day four, she required 10 L of supplemental oxygen. Repeat CT demonstrated new diffuse bilateral ground-glass opacities and small pleural effusions with persistent hilar lymphadenopathy (Figure 1B). Differential diagnoses included histoplasmosis, blastomycosis, tuberculosis, sarcoidosis, and lymphoma. Bronchoscopy with BAL and EBUS-guided lymph node aspiration showed 19% eosinophils without malignant cells; cultures for bacteria, fungi, and mycobacteria were negative. Histoplasma antibody testing revealed a weakly positive mycelial titer (1:4).Given worsening respiratory status and suspected fungal infection, empiric liposomal amphotericin B was initiated, followed by oral itraconazole after clinical improvement. She was discharged on 2 L of oxygen. Follow-up CT two weeks later showed resolution of opacities and reduction of the left upper lobe nodule to 7 × 6 mm (Figure 1C). Repeat serology confirmed Histoplasma infection with positive mycelial and yeast antibodies. Discussion This case illustrates that acute pulmonary histoplasmosis can mimic malignancy in immunocompetent hosts. Early serologic tests may be negative, and empiric antifungal therapy should be considered when clinical suspicion is high, especially in patients from endemic areas who fail antibiotic therapy. Conclusion Acute pulmonary histoplasmosis should remain in the differential diagnosis for patients from endemic regions presenting with fever, lymphadenopathy, and pulmonary nodules. Early recognition and antifungal treatment can lead to full recovery and prevent disease progression. This abstract is funded by: None