Coexistence of cat scratch disease lymphadenitis and active pulmonary tuberculosis in an immunocompetent host – a case report with metagenomic diagnosis and literature review

Cat scratch disease (CSD), caused by <i>Bartonella henselae (B. henselae)</i>, typically presents as localized swelling of lymph nodes following a scratch or bite from a cat. It is crucial to differentiate CSD from tuberculosis (TB), particularly in regions where TB is prevalent. This report describes a 56-year-old man who exhibited bilateral swelling of the cervical lymph nodes. Initially, he was suspected to have tuberculous lymphadenitis due to the granulomatous changes observed in a biopsy of the lymph nodes, typical signs of TB on a chest CT scan, and a positive result from an interferon-gamma release assay (IGRA). He was subsequently referred to our hospital for TB treatment. Testing of bronchoalveolar lavage fluid confirmed the presence of TB-DNA, indicating active pulmonary tuberculosis (PTB). However, further investigation revealed recent cat contact. This led to the identification of a <i>B. henselae</i> infection using metagenomic pathogen detection workflow (MetaPath™) on formalin-fixed paraffin-embedded (FFPE) histopathological sections from a cervical lymph node specimen obtained at an external hospital, which confirmed the diagnosis of CSD and ruled out TB. Through a review of the literature, we found that this represents the first documented case of concurrent active PTB and CSD-related lymphadenitis in an immunocompetent individual. It highlights the diagnostic challenges in distinguishing CSD from TB in cases of granulomatous lymphadenitis and emphasizes the need to consider CSD in patients with a history of cat exposure, showcasing the pivotal role of advanced metagenomic diagnostics in accurately diagnosing CSD.