A case of membranous nephropathy secondary to asymptomatic Graves' disease.

Although cases of secondary membranous nephropathy associated with autoimmune thyroid disease (AITD) have been reported, most of them, if not all, present with symptomatic thyroid disease. Here we report an asymptomatic case of AITD complicated with secondary membranous nephropathy. A 16-year-old girl was referred to our institute because of proteinuria found by an annual medical checkup. Urinalysis showed a urinary protein creatinine ratio (UPCR) of 3.0 g/gCre. Blood examination revealed that she had Graves' disease, although she did not have any symptoms of hyperthyroidism such as weight loss, anxiety, tremor, tachycardia, or eye symptoms. In a kidney biopsy, periodic acid silver-methenamine staining showed spike formation in the basement membrane. Electron microscopy showed electron-dense deposits on the epithelial side of the glomerular basement membrane. Immunofluorescent staining showed co-localization of thyroid peroxidase and IgG deposition along the glomerular capillary walls. A diagnosis of membranous nephropathy secondary to asymptomatic Graves' disease was made on the basis of results of the examinations. Treatment with thiamazole added to enalapril improved proteinuria (reduction of UPCR to 0.83 g/gCr) and hypoalbuminemia. Consideration should be given to the possibility of AITD in differential diagnosis of etiologies of membranous nephropathy even when typical symptoms of AITD are lacking.