CT-296 Isolated Bone Marrow Infiltration by Streptococcus Pneumoniae: An Unusual Etiology of Fever of Unknown Origin

Fever of unknown origin (FUO) in adults is defined as a temperature >38.3°C lasting for more than 3 weeks with no obvious source despite appropriate investigation. The differential diagnoses are infections, malignancies, autoimmune conditions, and miscellaneous. To our knowledge, isolated bone marrow infiltration by Streptococcus pneumoniae without bacteremia has not been reported yet in the literature. We report the case of a 48-year-old female patient, previously healthy, who presented for persistent fever of one-week duration. Initially, she complained of a 39°C fever without other associated symptoms except for daily night sweats. A complete infectious workup, including a full-body CT scan and screening for fungal or bacterial etiologies, was negative. Additionally, both transthoracic and transesophageal echocardiograms eliminated any signs of endocarditis. Subsequently, over the next two weeks, a complete autoimmune workup to test for a possible underlying rheumatologic disease was done but was all negative. To complete the endless FUO workup and in view of high suspicion of a malignancy, the patient performed an (FDG) PET CT scan along with a bone marrow biopsy that were both negative for any signs of malignancy, thus excluding any lymphoproliferative disease. One month after persistent fever, pan-cultures were serially repeated and remained negative. After developing a grade I thrombocytopenia, bone marrow aspirate with bone marrow culture were performed: no signs of malignancy or infiltration were found on the medullogram, but surprisingly, and after 48 hours of incubation, the bone marrow cultures turned positive for multi-sensitive Streptococcus pneumonia. We treated the patient with intramuscular ceftriaxone for an empirical period of 2 weeks. After only 3 doses of ceftriaxone, the fever subsided and the night sweats started to decrease gradually. After receiving a total of 14 days of antibiotics, we only monitored the patient clinically, without repeating the bone marrow cultures. Clinicians must be aware of this rare and unusual etiology of FUO. Bone marrow studies are routinely performed to exclude any lymphoproliferative disorder. In this perspective, we could draw a bone marrow culture while performing the regular aspiration studies to exclude possible isolated bone marrow infiltration by bacterial microorganisms.