Background/Purpose: In patients with septic arthritis, the white blood cell count in the synovial fluid is classically >50,000 cells/μL. While a microorganism must be identified in the synovial fluid to make a definitive diagnosis, the clinician often relies on the synovial white cell count to guide management prior to the culture results. There are few studies detailing the synovial fluid profile of patients with acquired neutropenia and septic arthritis. We performed a retrospective study to investigate synovial fluid white cell counts in neutropenic patients with culture positive septic arthritis.

Methods: Using ICD-9 and ICD-10 codes, we identified patients who carried both “septic arthritis” and “neutropenia” diagnoses at the University of Virginia Medical Center between January 2000 – January 2018. Twenty-six patients fulfilled these initial criteria. Charts were then reviewed individually to identify patients with an absolute neutrophil count (ANC) of less than 1000 cells/μL and synovial fluid cultures that confirmed septic arthritis.

Results: Three patients met the above criteria. The first patient was a 62 year old male with acute myelogenous leukemia. After induction chemotherapy, he presented with neutropenic fever secondary to Candida tropicalis candidemia. His course was complicated by septic arthritis of the right shoulder with synovial fluid cultures growing the same species of Candida. Aspiration of the joint revealed a synovial fluid count of 2 WBCs/μL. His total peripheral WBC count at the time of the arthrocentesis was 122 cells/μL (ANC undetectable). The second case was an 80 year old female with acute myelogenous leukemia. She presented after induction chemotherapy with neutropenic fever secondary to coagulase-negative Staphylococcus bacteremia. She developed septic arthritis of the right knee that grew this bacteria as well. Aspiration of the synovial fluid yielded a cell count of 9 total WBCs/μL. Her ANC was 110 cells/μL. The final patient was a 64 year old male with multiple myeloma and ESRD. He presented with neutropenic fever secondary to Vancomycin-resistant Enterococcus faecium (VRE). He developed septic arthritis of the right knee with synovial fluid cultures also growing VRE. His synovial fluid cell count was 22,125 WBCs/μL. His ANC was 730 cells/μL at that time of his septic arthritis diagnosis.

Conclusion: In patients with acquired neutropenia and septic arthritis, the degree of peripheral neutropenia correlates with the synovial fluid white blood cell count. Neutropenic patients with a total ANC above 500 cells/μL appear to be able to mount a modest inflammatory response in the infected joint, whereas patients with an ANC below 500 cells/μL may have normal synovial fluid white cell counts. Clinicians should maintain a high level of suspicion for septic arthritis in neutropenic patients with joint pain and swelling even in the face of a normal synovial fluid white cell count. Synovial fluid cultures are essential in establishing the diagnosis of septic arthritis.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/synovial-fluid-profile-in-neutropenic-patients-with-septic-arthritis/