Mercury-Induced Membranous Nephropathy in a Young Emirati Woman: A Hidden Threat in Cosmetic Creams

Introduction: Membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults. While many cases are idiopathic and associated with autoantibodies such as anti-PLA2R, others are secondary to drugs, infections, malignancy, or toxins. Mercury exposure, especially via unregulated skin-lightening creams, represents a rare but reversible trigger of secondary MN. Case Description: A 19-year-old previously healthy Emirati woman initially presented with fever and a generalized erythematous rash. Months later, she developed progressive lower limb edema and periorbital puffiness. Laboratory workup revealed nephrotic-range proteinuria (urine PCR 9 g/g), hypoalbuminemia (1.8 g/dL), and preserved renal function. Comprehensive autoimmune and infectious serologies, including ANA, ANCA, anti-dsDNA, ENA, and serum PLA2R antibodies, were negative. Renal biopsy showed features consistent with MN: granular capillary wall staining for IgG, C3, kappa, and lambda by immunofluorescence, and negative glomerular PLA2R staining—raising suspicion for a secondary cause Discussion: A detailed environmental history revealed daily use of unlabeled skin-lightening creams for 3–6 months prior to symptom onset. Toxicology confirmed mercury exposure with blood mercury level of 12 μg/L (ref ≤2.0) and urine mercury level of 93 μg/L (ref ≤1.0), supporting the diagnosis of mercury-induced MN. Treatment and Outcome: The patient discontinued the creams and received corticosteroids, rituximab (2 doses), cyclosporine, and ACE inhibitor therapy. Over four months, her proteinuria declined to 1.5 g/day, with improved serum albumin and reduction in blood mercury levels. Conclusion: This case highlights the importance of environmental exposure history in young patients with PLA2R-negative MN. Mercury-induced MN is an under-recognized but treatable condition. Early identification and removal of the offending agent can result in clinical remission. Greater awareness and regulation of mercury-containing cosmetic products are urgently needed to prevent similar cases