Differential Diagnosis for Nephrotic Syndrome in a 67-Year-Old Man
Single Most Likely Diagnosis
- D. Renal AL amyloidosis: The kidney biopsy showing expansion of the mesangial areas by deposits of homogenous, pale eosinophilic material that are positive with Congo red staining and demonstrate apple-green birefringence when viewed under polarized light is characteristic of amyloidosis. The presence of nephrotic syndrome with significant proteinuria (12,000 mg/24 h) and the specific biopsy findings point towards renal AL amyloidosis as the most likely diagnosis.
Other Likely Diagnoses
- A. Diabetic kidney disease: Although the patient has a 7-year history of well-controlled type 2 diabetes mellitus, the absence of retinopathy, neuropathy, or clinically evident vascular disease, along with the specific kidney biopsy findings, makes diabetic kidney disease less likely. However, the recent increase in creatinine levels could suggest some degree of diabetic kidney involvement.
- C. Membranous nephropathy: This is a common cause of nephrotic syndrome in adults, but the biopsy findings described do not support this diagnosis. Membranous nephropathy typically shows thickening of the glomerular basement membrane with subepithelial deposits.
Do Not Miss Diagnoses
- B. IgA nephropathy: Although less likely given the biopsy findings, IgA nephropathy can sometimes present with nephrotic syndrome. It is crucial to consider this diagnosis due to its potential for rapid progression and the importance of early treatment. However, the specific findings of Congo red positivity and apple-green birefringence under polarized light are not characteristic of IgA nephropathy.
Rare Diagnoses
- Fibrillary glomerulonephritis: This rare condition could present with nephrotic syndrome and has distinctive fibrillary deposits on electron microscopy. However, the biopsy findings described are more consistent with amyloidosis.
- Light-chain deposition disease: This condition involves the deposition of light chains in the kidney and can cause nephrotic syndrome. While it is a consideration in patients with monoclonal gammopathies, the specific biopsy findings and the absence of other suggestive features make it less likely in this case.