Bucillamine-induced membranous nephropathy with crescent formation in a patient with rheumatoid arthritis: case report and literature review

Membranous Nephropathy and Anti-Podocytes Antibodies: Implications for the Diagnostic Workup and Disease Management

The discovery of circulating antibodies specific for native podocyte antigens has transformed the diagnostic workup and greatly improved management of idiopathic membranous nephropathy (iMN). In addition, their identification has clearly characterized iMN as a largely autoimmune disorder. Anti-PLA2R1 antibodies are detected in approximately 70% to 80% and anti-THSD7A antibodies in only 2% of adult patients with iMN. The presence of anti-THSD7A antibodies is associated with increased risk of malignancy. The assessment of PLA2R1 and THSD7A antigen expression in glomerular immune deposits has a better sensitivity than measurement of the corresponding autoantibodies. Therefore, in the presence of circulating anti-podocytes autoantibodies and/or enhanced expression of PLA2R1 and THSD7A antigens MN should be considered as primary MN (pMN). Anti-PLA2R1 or anti-THSD7A autoantibodies have been proposed as biomarkers of autoimmune disease activity and their blood levels should be regularly monitored in pMN to evaluate disease activity and predict outcomes. We propose a revised clinical workup flow for patients with MN that recommends assessment of kidney biopsy for PLA2R1 and THSD7A antigen expression, screening for circulating anti-podocytes antibodies, and assessment for secondary causes, especially cancer, in patients with THSD7A antibodies. Persistence of anti-podocyte antibodies for 6 months or their increase in association with nephrotic proteinuria should lead to the introduction of immunosuppressive therapies. Recent data have reported the efficacy and safety of new specific therapies targeting B cells (anti-CD20 antibodies, inhibitors of proteasome) in pMN which should lead to an update of currently outdated treatment guidelines.

Acute interstitial nephritis with membranous nephropathy in bucillamine-treated rheumatoid arthritis

In bucillamine-treated patients, persistent proteinuria caused by membranous nephropathy (MN) is a major adverse effect affecting the kidneys. We experienced a case of acute interstitial nephritis (AIN) with MN caused by bucillamine. An 81-year-old Japanese woman with a past medical history of rheumatoid arthritis and hypertension presented with a fever, epigastric pain, and nausea of 1 week's duration. She had commenced bucillamine 4 months earlier. At the time of admission, her baseline creatinine (0.8 mg/dl) had risen to 6.8 mg/dl. A renal biopsy revealed AIN with concomitant MN. Renal function gradually improved after bucillamine administration was stopped. In addition to MN, bucillamine can cause AIN, which requires a renal biopsy for definitive diagnosis. Given the host of pathological findings that tend to develop in patients using bucillamine, patients receiving the drug who present with symptoms of acute kidney injury should undergo a renal biopsy to determine the presence of AIN.