Sjögren's Syndrome Overlap With Lupus Nephritis: A Case Report and Literature Review of a Rare Entity

Overlap syndrome is a connective tissue disorder that satisfies the diagnostic criteria for at least two well-known autoimmune diseases. In this report, we describe a rare case of lupus overlap in an elderly woman with primary Sjögren's syndrome who presented with features of nephritic-nephrotic syndrome and renal biopsy results typical of lupus nephritis combined with multiple positive autoantibodies. The kidney biopsy results were assigned the highest weightage based on the revised 2019 systemic lupus erythematosus (SLE) classification criteria developed by the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR). The patient's condition significantly improved after appropriate immunosuppressive therapy was initiated. With the revised ACR/EULAR-2019 criteria, we anticipate that more SLE patients with typical lupus nephritis biopsy findings will be diagnosed accurately.