Kikuchi-Fujimoto-Like Renal Involvement in Autoimmune Disease.

Introduction: Kikuchi-Fujimoto Disease (KFD) is a rare, self-limiting disorder primarily involving lymph nodes and characterized by necrotizing lymphohistiocytic inflammation with prominent apoptotic debris. Extranodal involvement has been described, but KF-like necroinflammation has only rarely been documented in kidney biopsies. Methods: We retrospectively reviewed data from 3 institutions over 20 years and identified 9 patients with native kidney biopsies showing KF-like interstitial necroinflammation and compared the clinical and pathologic features with 8 patients with systemic KFD and kidney biopsies. Results: A total of 8 of 9 patients with KF-like necroinflammation had previously diagnosed or suspected evolving systemic lupus erythematosus (SLE); none had systemic KFD. The most prominent finding in kidney biopsies was an atypical necroinflammatory interstitial infiltrate composed of histiocytes and lymphocytes with areas of brisk apoptosis, karyorrhectic debris, mitotic activity, and occasional large, atypical nuclei. The majority had limited or no glomerular involvement, and when present, this usually consisted of focal, mild active or chronic lesions with modest immune complex deposition. In comparison, in the 8 patients with systemic KFD, kidney biopsy findings were attributable to lupus nephritis (LN) in 4 of 5 patients with SLE, including 3 with membranous LN. No patient with systemic KFD had KF-like renal interstitial necroinflammation. Conclusions: Although lymphohistiocytic inflammation with prominent karyorrhexis most commonly manifests as a necrotizing lymphadenitis or dermatitis in both KFD and SLE, our study reveals that this distinctive pattern may also be recognized as an unusual interstitial nephritis, most commonly associated with SLE and seen in biopsies with limited glomerular involvement.