Rheumatoid factor positivity in ANCA-negative eosinophilic granulomatosis with polyangiitis: cardiac mimicry, mononeuritis multiplex, and long-term outcome in a case-based systematic review

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare small- to medium-vessel vasculitis characterized by asthma, eosinophilia, and multisystem involvement. Diagnosis is challenging in ANCA-negative disease, particularly when misleading serology is present. We describe a 42-year-old woman with long-standing asthma and a rheumatoid factor (RF) of 322 IU/mL, who initially presented with myocardial infarction–like cardiac involvement with non-obstructive coronary arteries. Over the subsequent seven months, progressive eosinophilia, chronic rhinosinusitis with nasal polyposis, and mononeuritis multiplex emerged. ANCA-negative EGPA was diagnosed after connective tissue disease, infection, malignancy, and other causes of hypereosinophilia were excluded. She was treated with prednisolone and azathioprine and subsequently remained off immunosuppressive therapy for more than nine years without reported relapse. On later clinical reassessment, she remained stable apart from mild residual neuropathic symptoms. We also conducted a case-based review following the CABARET standards, searching PubMed/MEDLINE, Scopus, Embase, and Web of Science up to 15 August 2026. We identified 38 published cases of ANCA-negative, RF-positive EGPA, 36 of them without pre-existing rheumatoid arthritis. In these 36, the median age was 53 years and 69% were female. Peripheral neuropathy was reported in 72% and cardiac involvement in 47%; with both occurring in 25%; two patients died of cardiac causes. Among 12 cases with sufficient data to standardize RF relative to the assay upper limit of normal, 75% had RF levels > 3 × ULN. Reporting was often incomplete: both MPO- and PR3-ANCA were documented in only 42% of cases and anti-CCP in 11%. No included published case reported prolonged treatment-free remission, although follow-up and treatment status were incompletely reported in several cases. Based on these gaps, the authors propose a reporting checklist for future EGPA case reports. RF positivity, even at high titer, should not dissuade clinicians from considering EGPA when asthma, eosinophilia, ENT disease, neuropathy, or other compatible manifestations are present.