Renal Necrotizing Histiocytic Lesions in a Patient with Systemic Lupus Erythematosus (SLE)

Introduction: Patients with SLE can develop lupus lymphadenitis (LL) with necrotizing lesions in lymph nodes and is difficult to distinguish from Kikuchi-Fujimoto Disease (KFD). There have been no cases depicting histological evidence of necrotizing lymphadenitis in the kidney Case Description: A 35 year old female with SLE presented with fevers & cervical lymphadenopathy. Extensive workup for infections was negative. A lymph node and native kidney biopsy were performed (figures 1 & 2). These showed a necrotizing inflammatory process with CD8 + T cells, plasma cells and macrophages Discussion: KFD & LL have both distinct and overlapping features. On histology, KFD is characterized by patchy areas of necrosis with abundant karyorrhectic nuclear debris. Neutrophils & eosinophils are typically absent. Immunohistochemical testing often shows CD3 & CD8 T cells. Presence of neutrophils, hematoxylin bodies, & abundant plasma cells is more consistent with LL. C4d staining (more common in LL) may be useful in distinguishing the two. There are reports of AKI in patients with KFD, however, direct involvement of renal parenchyma by necrotizing inflammation recapitulating lymphadenitis is not documented. One explanation is an over-active immune response that leads to localized inflammation in nearby tissues. KFD is typically limited to lymph nodes, so how it spreads to distant organs is less clear. Possible explanations include migration of inflammatory cells from elsewhere, or de novo inflammatory process that initiated in the kidney. It is unclear why this necrosis predominantly involves histiocytes and not neutrophils. Our case highlights another entity that can be encountered in a patient with SLE & the need for renal biopsies when a diagnosis is not clear. Obtaining an adequate sample is important to not miss other pathological processes