Eosinophilic granulomatosis with polyangiitis coexisting with multiple myeloma: independent entities or coexistence? A case report.

Eosinophilic granulomatosis with polyangiitis (EGPA) represents a systemic necrotizing vasculitis characterized by prominent peripheral eosinophilia. Concomitant plasma cell dyscrasias in the context of EGPA remain exceedingly rare in clinical literature. This paper presents a case of a 49-year-old female patient with recurrent diarrhea, rash, fever, and wheezing. The patient was initially diagnosed with multiple myeloma (MM) due to significant elevation of M protein and immature plasma cells in the bone marrow. However, chemotherapy failed to alleviate her condition, while standardized EGPA treatment achieved disease control. This case of EGPA with clinical manifestations of MM prompts us to consider whether the clinical presentation should follow Occam's razor or Hickam's dictum. Ultimately, we hypothesize that EGPA-induced eosinophil (EOS) perturbs the bone marrow hematopoietic niche. Through the Th2-mediated cytokine milieu, this microenvironment may trigger a reactive, "pseudo-malignant" expansion of plasma cells.