Kikuchi Disease After SARS-CoV-2 Vaccination: A Case Report With Immunohistochemical Analyses.

SARS-CoV-2 vaccines have been administered in many countries after the COVID-19 pandemic. Lymphadenopathy is a side effect of SARS-CoV-2 vaccine. We report a rare example of Kikuchi disease in the cervical lymph nodes after SARS-CoV-2 vaccination. A 41-year-old man complained of a swollen neck and fever 9 days after the first dose of SARS-CoV-2 mRNA-1273 vaccine. Computed tomography revealed enlarged cervical lymph nodes. Fine needle aspiration and resection were performed, and the clinicopathological diagnosis was consistent with Kikuchi disease. Histologically, the resected lymph nodes lost their polarity, and many histiocytes were aggregated with karyorrhectic nuclear debris and apoptosis. SARS-CoV-2 positive cells were small lymphocytes detected by immunohistochemistry. This is the first report that demonstrated SARS-CoV-2 expression in Kikuchi disease post-SARS-CoV-2 vaccination.