Atypical lymphoproliferative disorder and acquired angioedema in systemic lupus erythematosus and Sjögren's syndrome: A diagnostic challenge.

We report a case of a 33-year-old woman presenting with facial erythema, pharyngitis, and progressive cervical lymphadenopathy with tongue, pharyngeal, and laryngeal edema. Laboratory evaluations revealed an elevated soluble interleukin-2 receptor level, positive antinuclear, double-stranded DNA, Sjögren's syndrome-related antigen A antibodies, and decreased complement levels. Salivary gland studies confirmed Sjögren's syndrome, and together with serological findings, the patient fulfilled criteria for systemic lupus erythematosus. Although Positron emission tomography-computed tomography findings raised suspicion for malignant lymphoma, a cervical lymph node biopsy demonstrated interfollicular expansion, proliferation of small blood vessels with prominent endothelial cells, and large immunoblasts, consistent with atypical lymphoplasmacytic and immunoblastic proliferation. Despite clinical evidence of angioedema on endoscopic examination, complement levels and C1-inhibitor activity were normal, suggesting a non-complement-mediated mechanism. The patient was initially treated with hydroxychloroquine for systemic lupus erythematosus; however, worsening symptoms required prednisolone therapy, leading to significant clinical improvement. Recurrence during steroid tapering was managed by adjusting the steroid dose and adding mycophenolate mofetil. This case emphasises the importance of comprehensive evaluation to differentiate atypical lymphoplasmacytic and immunoblastic proliferation from malignant lymphoma and to recognise atypical acquired angioedema in autoimmune disease.