Background/Purpose: ANCA associated vasculitis (AAV) is a severe autoimmune disorder with substantial morbidity and mortality. Establishing the diagnosis might be challenging due to the existence of noteworthy mimickers, most notably infective endocarditis (IE) and drug-induced AAV. We aimed to identify differences in initial labs, serologies, clinical manifestations, and histopathology findings with the goal recognizing diagnostic clues that can raise suspicion for a secondary process.

Methods: A retrospective chart review was conducted on patients with glomerulonephritis (GN) secondary to IE, drug-induced AAV and primary AAV, from January 1, 2008, to January 1, 2024. Patients were filtered using SNOMED clinical terms of vasculitis and GN and any positive ANCA test. GN diagnosis was established either histologically or clinically by elevated creatinine and new onset hematuria with active urinary sediment. IE diagnosis was established by modified Duke Criteria or positive PCR on removed valve. Primary and drug induced AAV diagnosis were established by vasculitis specialist. Blood counts, and serologies were collected prior to any treatment including glucocorticoids. Statistical analysis included the use of Kruskal-Wallis test for continuous variables and Chi-square test for categorical variables.

Results: Baseline characteristics are outlined in Table 1. There were 42 patients with IE related GN, 35 with drug-induced AAV, and 50 with primary AAV. Median age at diagnosis was 58.4, 70.7, and 59.1 years, respectively. Bartonella was the most common microorganism (52.4%) in the IE-related GN group, and almost all drug-induced AAV cases (97%) were linked to hydralazine.Baseline labs and serologies are detailed in Table 2. Initial blood counts showed that IE-related GN and drug-induced AAV patients commonly presented with leukopenia (42.8% and 48.5%, respectively) and thrombocytopenia (90.4% and 37.1%, respectively) and seldomly presented with thrombocytosis (0% and 2.8%, respectively). Primary AAV patients frequently presented with leukocytosis (80%) and thrombocytosis (68%), and rarely with leukopenia (2%) and thrombocytopenia (2%). Median initial leukocyte, neutrophil, lymphocyte, and platelet counts were higher in primary AAV compared to other groups (p< 0.001). Hypocomplementemia was found in 76.2% of IE-related GN and 80% of drug-induced AAV cases, compared to 22% in primary AAV (p< 0.001). Majority of patients underwent renal biopsy (Table 3). C3 was the most common immunofluorescence staining in IE-related GN and drug-induced AAV. Dialysis cessation at 6 months occurred in 75% of primary AAV patients, whereas 30.7% of IE related GN patients, and 18.7% of drug-induced AAV patients (p< 0.001). Six-month mortality was significantly higher in IE related GN and drug induced AAV compared to primary AAV (p< 0.001).

Conclusion: The presence of cytopenia including leukopenia and thrombocytopenia, along with low complement levels upon presentation of IE related GN and drug-induced AAV can help clinicians to discern from primary AAV. Early recognition of these mimickers is critical, as they are associated with lower rates of renal recovery and higher six-month mortality.

Table 1. Summary of study population characteristics and clinical presentation.

Table 2. Laboratory values and serologies..

Table 3. Renal biopsy findings and outcomes.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/differentiating-primary-anti-neutrophil-cytoplasmic-antibody-anca-associated-vasculitis-from-secondary-forms-2/