Abstract
Rheumatoid arthritis is an autoimmune disease primarily characterized by chronic symmetric arthritis. While rheumatoid arthritis with elevated eosinophils exhibits distinct clinical features, the potential coexistence of immunoglobulin (Ig)G4-related disease warrants clinical vigilance. This article reports a case of a patient presenting with polyarticular swelling and pain accompanied by morning stiffness. Positive tests for anti-keratin antibody, anti-cyclic citrullinated peptide antibody, anti-perinuclear factor, and rheumatoid factor were observed with a significantly elevated erythrocyte sedimentation rate, leading to a definitive diagnosis of rheumatoid arthritis. The patient also exhibited elevated peripheral blood eosinophils and showed poor response to treatments, such as leflunomide and tripterygium glycosides. After switching to methotrexate and tocilizumab, the patient's joint symptoms improved significantly, but peripheral blood eosinophilia showed no notable improvement. During the course of the disease, the patient developed lymphadenopathy and parotid gland enlargement. Lymph node ultrasound revealed a hypoechoic nodule in the left supraclavicular area, abnormal lymph nodes in both axillae and the right inguinal region, and visible lymph nodes in the bilateral cervical and left inguinal areas. Parotid ultrasound indicated hypoechoic nodules within both parotid glands and widening of the parotid ducts. Further bone marrow aspiration biopsy showed no significant abnormalities, while lymph node pathological biopsy suggested infiltration of IgG4-positive cells. Subsequent serum IgG4 testing revealed elevated level of IgG4. The patient was ultimately considered likely to have rheumatoid arthritis complicated with IgG4-related disease. Treatment was adjusted to regular infusions of rituximab (500 mg every six months), resulting in significant improvement of joint swelling and pain, as well as marked reductions in C-reactive protein and eosinophil levels, achieving disease remission. Through case analysis and literature review, this article discusses the diagnosis and treatment of rheumatoid arthritis patients with elevated eosinophils. For patients with rheumatoid arthritis with elevated eosinophils, it is necessary to be vigilant of the possibility of concurrent IgG4-related diseases. The use of rituximab provides novel perspectives for clinical treatment strategies.