Acute toxoplasmosis mimicking metastatic lymphadenopathy of sarcoma

Abstract

Abstract Introduction: Clear cell sarcoma is a rare malignant neoplasm with the potential to metastasize to lymph nodes. We report herein a case of acute toxoplasmosis that mimicked metastatic lymphadenopathy from treated clear cell sarcoma on 18F-fluorodeoxyglucose positron emission tomography/computed tomography. Toxoplasmosis is usually asymptomatic in immunocompetent hosts. Acute acquired toxoplasmosis clinically manifests as lymphadenopathy predominantly involving the cervical nodes. Patient concerns: A 45-year-old woman underwent resection of subcutaneous clear cell sarcoma of the right knee. PET/CT performed four years after surgery revealed multiple sites of lymphadenopathy with avid FDG uptake in the right neck, left axilla, left pulmonary hilum, and right inguinal regions. The patient was afebrile and asymptomatic. Metastases were suspected and excisional biopsy of a left axillary node was performed. Diagnoses: Histopathological examination revealed reactive lymphadenitis, suggesting toxoplasmic infection without evidence of malignancy. Serum levels of toxoplasmic immunoglobulin (Ig)M antibodies were high. Serum IgG antibodies were significantly elevated in six weeks from the PET/CT examination. The patient had a cat at home, which could have represented the source of infection. Interventions: The patient was carefully monitored using regular imaging examinations. Outcomes: FDG accumulations resolved spontaneously on follow-up examination one year later. Conclusion: We report a case in which toxoplasmic lymphadenitis mimicked malignant lymphadenopathy. Lymphadenopathy at a distant site from the primary malignancy with FDG avidity may be due to infectious or inflammatory conditions, creating false-positive results.