Purpura as the initial manifestation of IgG4-related disease with concomitant systemic lupus erythematosus: a case report

This case report describes the case of a 61-year-old man who initially presented with purpura. He was subsequently diagnosed with coexisting immunoglobulin G4 (IgG4)-related tubulointerstitial nephritis (TIN) and class II lupus nephritis. The patient was treated with a combination of prednisone, hydroxychloroquine, and mycophenolate mofetil. Within one month of treatment, the purpura resolved, and qualitative urine protein testing turned negative. During an eight-month follow-up period, sustained clinical improvement was observed. This study, for the first time, highlights purpura as the initial presentation of concurrent IgG4-related disease and systemic lupus erythematosus (SLE). It also describes a novel renal pathological overlap characterized by IgG4-related tubulointerstitial injury alongside lupus-induced mesangioproliferative glomerulonephritis. These findings provide new insights into the diagnosis, management, and prognosis of this rare condition.