Disseminated Bartonella henselae Infection in a Patient With Relapsed/Refractory Multiple Myeloma Following Autologous Stem Cell Transplantation

<i>Bartonella henselae</i> is the causative agent of cat scratch disease (CSD), a zoonotic illness primarily transmitted to humans through scratches or bites from cats and, less commonly, by cat fleas or lice. While the most common presentation is self-limited regional lymphadenopathy in immunocompetent individuals, in immunocompromised patients, such as organ transplant recipients, it can cause systemic infections. This report describes a case of disseminated <i>B. henselae</i> infection in a 66-year-old man with relapsed/refractory multiple myeloma following conditioning chemotherapy and autologous stem cell transplantation (ASCT). <i>B. henselae</i> infection has not been well characterized in patients after ASCT. The patient presented with persistent fever and involvement of the liver and right inguinal lymph nodes after transplantation. Diagnosis was challenging due to nonspecific symptoms and initially negative routine tests; however, detection of <i>B. henselae</i> DNA through polymerase chain reaction (PCR) in liver and lymph node biopsy specimens confirmed the infection. Following initiation of antibiotic therapy, the patient showed both symptomatic and radiological improvement. <i>Bartonella</i> infections remain poorly characterized in post-transplant patients. This case highlights the diagnostic challenges of atypical infections in immunocompromised individuals, particularly ASCT recipients, and underscores the importance of specialized diagnostic testing, including tissue PCR, for early diagnosis and targeted antimicrobial therapy.