Case Report: Atypical cat-scratch disease presenting as referred shoulder pain and deep lymphadenopathy in a pediatric patient.

BACKGROUND: Cat-scratch disease (CSD) is a zoonotic infection attributable to Bartonella henselae. Typical clinical manifestations include regional lymphadenopathy accompanied by primary cutaneous lesions that develop following exposure to cats. Although most patients present with typical regional lymphadenopathy, a subset of patients may develop atypical manifestations, which can complicate diagnosis. Owing to the nonspecific clinical features, CSD is prone to misdiagnosis or diagnostic omission. This report describes a pediatric case of atypical cat-scratch disease characterized by initial symptoms of fever and shoulder arthralgia, absence of superficial lymphadenopathy, and involvement of deep lymph nodes. This report aims to broaden clinicians' recognition of the diverse and atypical clinical manifestations of this disease.

CASE SUMMARY: An 11-year-old female patient presented to the hospital with persistent fever accompanied by left shoulder joint pain and restricted movement of the left upper extremity. Physical examination upon admission revealed no superficial lymphadenopathy or characteristic cutaneous lesions. Following empirical broad-spectrum antibiotic therapy, the patient continued to experience recurrent febrile episodes, with persistently elevated inflammatory markers. Subsequent magnetic resonance imaging (MRI) of the shoulder joint and contrast-enhanced computed tomography (CT) of the chest demonstrated multiple enlarged lymph nodes in the left axillary, supraclavicular, and deep cervical regions. Further history-taking disclosed recent exposure to cats. Histopathological examination of an axillary lymph node biopsy (hematoxylin-eosin staining) revealed suppurative granulomatous lymphadenitis. These H&E histopathological findings are merely supportive rather than confirmatory evidence for CSD, as we failed to perform Bartonella henselae-specific serology, PCR, Warthin-Starry silver staining or immunohistochemistry to identify the pathogen directly. The diagnosis was considered highly suggestive of atypical CSD based on integrated clinical, radiological, epidemiological, and histopathological findings. Upon diagnosis, the patient was administered doxycycline in combination with rifampicin for antimicrobial treatment. The patient's body temperature normalized, shoulder pain progressively resolved, and inflammatory markers returned to reference ranges. During a 3-month follow-up period, no disease recurrence was noted. Shoulder joint mobility was restored to normal, and no significant adverse drug reactions were observed.

CONCLUSION: In pediatric patients presenting with fever of unknown origin accompanied by musculoskeletal symptoms, suboptimal response to conventional anti-infective therapy, and absence of superficial lymphadenopathy, the possibility of atypical cat scratch disease should be considered. A detailed assessment of contact history with domestic animals, along with prompt deep lymph node imaging evaluation and histopathological biopsy, facilitates early and appropriate clinical diagnosis. Implementation of targeted antimicrobial therapy may improve clinical outcomes in affected children.