Case Report: Angioimmunoblastic T-cell lymphoma initially diagnosed as eosinophilic granulomatosis with polyangiitis.

Background: Eosinophilic granulomatosis with polyangiitis (EGPA) and angioimmunoblastic T-cell lymphoma (AITL) are distinct entities that can present with overlapping clinical features, posing a significant diagnostic challenge. This case highlights a critical diagnostic pitfall where AITL was initially misdiagnosed as EGPA. Case presentation: A 55-year-old man presented in 2021 with recurrent wheezing, dyspnea, chronic sinusitis, peripheral eosinophilia (7.35 × 10⁹/L), and skin rash, leading to an initial diagnosis of asthma and later EGPA. Despite treatment with systemic corticosteroids, omalizumab, and mepolizumab, his respiratory symptoms persisted, and lymphadenopathy progressed. A fine-needle lymph node biopsy initially suggested Kimura disease. In 2024, the appearance of a parotid mass prompted further investigation. A subsequent surgical lymph node biopsy in 2025 revealed an effaced nodal architecture with a proliferation of atypical T-cell positive for CD3, CD5, ICOS, and PD-1. T-cell receptor gene rearrangement demonstrated clonality, and Epstein-Barr virus-encoded RNA was detected in situ. These findings confirmed the diagnosis of AITL. Treatment was switched to the CHOP chemotherapy regimen, leading to symptomatic improvement and normalization of eosinophil counts. Conclusion: This case underscores that AITL can closely mimic EGPA, presenting with severe asthma, hypereosinophilia, sinusitis, and systemic symptoms. It emphasizes the necessity of considering underlying lymphoma in patients with suspected EGPA who show an atypical or refractory course to conventional therapy. A definitive diagnosis often requires an adequate tissue sample, preferably from a surgical lymph node biopsy, to avoid misdiagnosis and ensure appropriate management. Respiratory physicians should maintain a high index of suspicion for lymphoid malignancies in such complex presentations.