P3C248: Distal, Multifocal Osteomyelitis as a Complication of Disseminated Cat Scratch Disease

Introduction:

Introduction: Cat scratch disease (CSD) commonly presents in children with regional lymphadenopathy. In immunocompetent children, atypical manifestations are rare, and osteomyelitis is particularly infrequent. We present an unusual case of Bartonella henselae-associated multifocal osteomyelitis in an immunocompetent child.

Case Description: A previously healthy 11-year-old boy presented to the emergency department with fevers for two weeks, progressive, right-sided preauricular swelling, and acute onset of left hip pain and limp. He reported close exposure to kittens at home with previous scratches. His exam revealed right-sided 2 cm x 1 cm preauricular tender lymphadenopathy without overlying skin changes. Passive and active range of motion of the contralateral hip produced pain and his gait was antalgic, but there was no tenderness to palpation, edema, or erythema. Initial labs demonstrated elevated inflammatory markers (Table 1). Ultrasound demonstrated nonspecific preauricular lymphadenitis without abscess. Facial computerized tomography (CT) showed a necrotic lymph node conglomerate. Magnetic resonance imaging (MRI) identified multifocal bone marrow signal abnormalities of the left proximal femur, bilateral distal femurs, and bilateral proximal tibiae (Image 1). Biopsy was deferred while awaiting initial serologic testing. Empiric treatment with ceftriaxone and clindamycin was started, and the patient was discharged home on hospital day three with oral doxycycline and rifampin. His Bartonella IgG serology resulted positive two weeks after discharge, and he completed a four-week course of doxycycline and rifampin with improvement of his CRP, hip pain and lymphadenopathy.

Discussion: CSD is caused by Bartonella henselae, a gram-negative aerobic bacterium. In immunocompetent children, it typically presents with self-limiting, regional lymphadenopathy. Atypical infections, due to hematogenous spread distal to the inoculation site, are uncommon and most often involve extra-nodal sites, e.g., eyes, nervous system, viscera, and musculoskeletal system. Musculoskeletal manifestations include arthropathy, myalgia, and rarely osteomyelitis (0.27-3% of CSD cases).
The largest case series reports a predilection for the axial skeleton, including pelvis, vertebrae, and skull. The preferred diagnostic approach includes clinical and serologic correlation, with titers ≥1:512 considered abnormal. Other approaches include bone or soft tissue biopsy (invasive with often non-specific findings); culture (low diagnostic yield); and molecular testing (not widely available)5.
The differential diagnosis for multifocal osteomyelitis includes chronic infectious osteomyelitis, malignancy, histiocytosis, chronic recurrent multifocal osteomyelitis, and vitamin deficiencies. Given the highly suggestive clinical presentation and elevated inflammatory markers, we started presumptive treatment for Bartonella osteomyelitis. Since uncomplicated Bartonella is typically self-limited, antibiotics are only indicated for disseminated cases. Common regimens include doxycycline with either rifampin or azithromycin1, for four to six weeks.

Conclusion: Osteomyelitis due to disseminated CSD remains a rare but important diagnostic consideration in children presenting with lymphadenopathy, prolonged fevers, musculoskeletal complaints, and close contact with cats.