Fever with Eosinophilia and Bone Marrow Granulomas in an Elderly Female: A Rare Case Report and Literature Review

Background Diagnosing fever of unknown origin (FUO) in elderly patients remains particularly challenging. When FUO is accompanied by marked eosinophilia and progressive cytopenia, the differential diagnosis expands considerably and becomes more complex. Bone marrow granulomas represent an uncommon pathological finding and may arise from a wide range of etiologies, including infectious diseases, malignancies, and autoimmune disorders. Case presentation We report the case of a 79-year-old woman who was admitted with a six-day history of high-grade fever. Laboratory evaluation revealed peripheral blood eosinophilia, thrombocytopenia, and markedly elevated inflammatory markers. Comprehensive microbiological investigations, including blood cultures and respiratory pathogen screening, failed to identify a causative organism. Empirical anti-infective therapy was initially ineffective, and the patient’s condition progressed to pancytopenia, with neutropenia as the predominant feature. Bone marrow aspiration and biopsy demonstrated a hypocellular marrow with grade 3 fibrosis and non-caseating granuloma formation, accompanied by CD3⁺ T-cell infiltration. Based on the clinical course and pathological findings, a diagnosis of infection-related myelosuppression associated with granulomatous bone marrow involvement was established. Treatment with mezlocillin in combination with dexamethasone resulted in rapid defervescence and gradual recovery of peripheral blood counts. The patient was subsequently discharged in clinical remission. At one-month follow-up, there was no evidence of disease recurrence, and complete blood count parameters had returned to normal. Conclusions This case underscores the importance of considering bone marrow granulomas in elderly patients presenting with FUO accompanied by eosinophilia and hematologic abnormalities. Bone marrow biopsy plays a pivotal role in establishing a definitive diagnosis in such complex clinical scenarios. Furthermore, even in the absence of an identifiable pathogen, empirical treatment with broad-spectrum antibiotics in combination with corticosteroids may represent an effective therapeutic approach for mitigating excessive inflammatory responses and reversing infection-associated myelosuppression.