Introduction: Multifocal osteomyelitis secondary to Bartonella henselae (B. henselae) is a rare clinical manifestation in children that can mimic chronic recurrent multifocal osteomyelitis (CRMO), with its indolent clinical course as well as similar findings on a Whole Body Magnetic Resonance Imaging (WB-MRI). Clinicians should be aware that disseminated B. henselae infection can be distinguished from CRMO, with epidemiologic link, serologic evidence, and visceral involvement (from hematologic spread). Case Presentation: A previously healthy 11-year-old African American male presented to emergency department (ED) for 12 days of fever (Tmax 104 F) at home, with associated headache and generalized weakness. He was diagnosed with viral illness by his pediatrician a few days prior, but his fevers were unrelenting despite antipyretic use. In the ED, his vital signs were normal, and physical examination was unremarkable. He had 2 cats at home, but had no other significant exposure or travel history. Laboratory tests showed elevated Erythrocyte Sedimentation Rate (85mm/hr) and C-Reactive Protein (6.6mg/dL). Transthoracic echocardiography (TEE) showed no vegetation, and peripheral blood culture showed no growth. On hospital day (HD) 3, a Whole-Body Magnetic Resonance Imaging (WB MRI) was performed for concerns of CRMO, which revealed multiple bony lesions with abnormal marrow edema. Though oral naproxen was started immediately, given that CRMO is a diagnosis of exclusion, extensive work-up for other etiologies were also explored. On HD4, right tibial bone marrow biopsy, as well as serologic tests for B. henselae were done. A few days later, the serologic tests came back positive for B. henselae with IgM >1:20, IgG > 1:1,024. Abdominal ultrasound showed small multiple hypoechoic lesions within liver and spleen, which were consistent with visceral involvement of disseminated B. henselae infection. He was started on azithromycin and rifampin, to which he responded with some clinical improvement. However, his fevers recurred 5 days into therapy, and treatment regimen was modified to ciprofloxacin and rifampin. Immunologic work-up showed normal dihydrorhodamine (DHR) flow cytometry assay, appropriate immunoglobulin IgG, IgA, IgM levels, and negative result for human immunodeficiency virus. With marked clinical improvement with no recurrent fevers for 3 days, he was discharged home with a total of 4-6 weeks of therapy (ciprofloxacin and rifampin). Discussion: CRMO is a diagnosis of exclusion, thus, clinicians should look for other explainable causes, especially for B. henselae infection, in patients with cat exposures. Currently, there is no consensus on antimicrobial choice and duration of therapy for disseminated B. henselae infection in immunocompetent children. Further studies need to be performed to better delineate optimal treatment course and prognosis.

Multiple areas of abnormal marrow edema, scattered throughout the appendicular skeleton in the metaphyseal regions, with suggestion of multiple sub-centimeter T2 hyperintense rounded-lesions scattered throughout the liver.

Multiple areas of abnormal marrow edema, scattered throughout the appendicular skeleton in the metaphyseal regions, with suggestion of multiple sub-centimeter T2 hyperintense rounded-lesions scattered throughout the liver.

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Liver: Several small, approximately 5 mm, hypoechoic lesions. Multiple small hypoechoic lesions are identified, measuring approximately 5 mm, similar to the liver lesions. The spleen measures 10 cm.

Liver: Several small, approximately 5 mm, hypoechoic lesions. Multiple small hypoechoic lesions are identified, measuring approximately 5 mm, similar to the liver lesions. The spleen measures 10 cm.

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