Proliferation of CD10+ mature plasmacytoid dendritic cells in lymph nodes of patients with chronic non-tuberculous mycobacterial infection: a case report.

BACKGROUND: Plasmacytoid dendritic cells are essential immune system components, critical in antiviral and antibacterial defense. Although plasmacytoid dendritic cells are typically present in small numbers in the peripheral blood, bone marrow, and lymph nodes, their expansion within the lymph nodes accompanied by CD10 expression is a relatively uncommon phenomenon. CASE PRESENTATION: A 54-year-old Chinese female had experienced recurrent lymphadenopathy for over 2 years. She was diagnosed with Mycobacterium chimaera infection more than 1 year before presentation, and her condition was assessed as being in remission 4 months prior. She was readmitted to the hospital because of lymphadenopathy and underwent a lymph node biopsy. Flow cytometry demonstrated a population of plasmacytoid dendritic cells with the phenotype CD3-CD4+CD10+CD123+CD303+, accounting for 2.95% of all nucleated cells. Histopathological examination confirmed plasmacytoid dendritic cell proliferation, with a proliferation index Ki-67 < 10%, partially positive CD10 expression, and negative TCL1 expression. Next-generation sequencing identified Mycobacterium intracellulare, ultimately confirming that the lymphadenopathy of the patient was caused by chronic nontuberculous mycobacterial infection. CONCLUSION: This is the first reported case of significant CD10+ mature plasmacytoid dendritic cell proliferation in the lymph nodes of a patient with chronic nontuberculous mycobacterial infection. Clinicians and pathologists should consider the possibility of plasmacytoid dendritic cell proliferation in patients with chronic or refractory nontuberculous mycobacterial infections, particularly in those with lymphadenopathy. Ultimately, this case report may contribute to the development of diagnostic strategies for related diseases.