Subclinical acute tubular necrosis potentially associated with red yeast rice consumption unexpectedly detected in a patient with membranous nephropathy

In March 2024, a significant public health issue involving red yeast rice supplements emerged in Japan, which may have been associated with several health problems, including kidney dysfunction. A 74-year-old man without a history of urinary abnormalities developed nephrotic syndrome 10 weeks after starting “Beni-Koji Choleste Help^®,” a red yeast rice supplement. Electron microscopy showed subepithelial and intramembranous dense deposits with abnormality of the glomerular basement membrane, which led to the diagnosis of long-standing membranous nephropathy. The diagnosis of phospholipase A2 receptor (PLA2R)-positive primary membranous nephropathy was confirmed via PLA2R-positive immunostaining. Furthermore, there were findings of focal tubular necrosis without unexplained cellular infiltration. Based on previous reports, it was suggested that red yeast rice-related products have triggered the acute tubular necrosis in the patient. His nephrotic syndrome reached partial remission with oral administration of prednisolone at an initial dose of 40 mg/day. This case indicates that membranous nephropathy was coincidentally accompanied by acute tubular necrosis that was potentially associated with red yeast rice-related health foods. It may be reasonable to state that individuals consuming red yeast rice-related health products may develop subclinical focal tubular necrosis even in the absence of overt clinical symptoms or laboratory abnormalities. The currently recognized health issues associated with red yeast rice-related health foods may only represent a small portion of the overall risks.