Pulmonary histoplasmosis presenting with a halo sign on CT in an immunocompetent patient

Histoplasmosis is a common endemic mycosis. Although most infections in immunocompetent individuals are self-limiting, some patients develop severe pneumonitis or other types of chronic pulmonary infection. Specific imaging findings depend on the organisms involved, the underlying condition of the patient, and his condition after immune depleting procedures. The disease process in immunocompetent patients is usually limited to a solitary nodule on chest X-rays or CT scans, but enlarged hilar or mediastinal lymph nodes can also be observed.(1) We report here the case of an immunocompetent patient with histoplasmosis who presented with a halo sign on CT. A 47-year-old man presented with dry cough, chest pain, fatigue, and fever, having started 15 days prior. He reported neither comorbidities nor a contact with environments with mold. The patient was negative for HIV by ELISA. Laboratory tests revealed leukocytosis, elevated C-reactive protein levels (33 mg/L), and hypertransaminasemia (three-fold higher than the upper limit of normal). CT scanning revealed a pulmonary nodule with a halo sign in his left lower lobe (Figure 1) and left para-hilar lymph nodes. Histological examination of a pulmonary biopsy sample obtained during bronchoscopy showed nonspecific inflammatory alterations. Cultures for mycobacteria and fungi were negative. Serology by counterimmunoelectrophoresis was positive for histoplasmosis. Treatment was initiated with itraconazole (400 mg/day). After 30 days, a CT scan showed that the size of the nodule was reduced by half.