Kannan Lakshmi
Nephrology, Pikeville Medical Center, Pikeville, USA.
Cureus. 2022 Sep 12;14(9):e29083. doi: 10.7759/cureus.29083. eCollection 2022 Sep.
Membranous nephropathy (MN) is a common etiology of nephrotic syndrome (NS) in Caucasian adults. With treatment strategies heavily dependent on differentiating between primary versus secondary MN, tissue diagnosis remains paramount in the setting of indeterminant serological studies and remains the gold standard. Direct immunofluorescence on frozen sections remains standard practice, though with inadequate kidney tissue, antigen retrieval with proteases on formalin-fixed paraffin-embedded tissue can be a viable alternative for direct immunofluorescence. We report a patient who presented with nephrotic syndrome, indeterminant serological workup including primary antigen phospholipase-2 receptor antibody (PLAR). Histology revealed a membranous pattern of injury with a negative standard panel of immunocomplex deposits on direct immunofluorescence. Upon re-examination of paraffin-embedded tissue via protease processing, Immunofluorescence unmasked membranous lupus nephritis. This case highlights the possibility of negative direct immunofluorescence on viable frozen tissue which is unmasked after protease treatment on formalin-fixed paraffin-embedded tissue sample revealing immunocomplex deposits.
膜性肾病（MN）是白种人成年人肾病综合征（NS）的常见病因。由于治疗策略严重依赖于区分原发性与继发性MN，在血清学研究不确定的情况下，组织诊断仍然至关重要，并且仍然是金标准。对冰冻切片进行直接免疫荧光检查仍然是标准做法，不过在肾组织不足的情况下，对福尔马林固定石蜡包埋组织用蛋白酶进行抗原修复可作为直接免疫荧光检查的可行替代方法。我们报告了一名表现为肾病综合征的患者，其血清学检查结果不确定，包括原发性抗原磷脂酶-2受体抗体（PLAR）。组织学显示为膜性损伤模式，直接免疫荧光检查免疫复合物沉积标准组结果为阴性。在通过蛋白酶处理对石蜡包埋组织进行重新检查时，免疫荧光检查揭示了膜性狼疮性肾炎。该病例突出了在可行的冰冻组织上直接免疫荧光检查结果为阴性的可能性，而在福尔马林固定石蜡包埋组织样本上进行蛋白酶处理后可揭示免疫复合物沉积。
