A 60-year-old diabetic patient presents with easy fatigability, weakness, and numbness of hands. The renal biopsy shows an amorphous substance that stained red with congo-red. What is the diagnosis?

The presentation of the patient, including easy fatigability, weakness, and numbness of the hands, combined with the renal biopsy findings, points clearly to the diagnosis of amyloidosis. The key factor in this scenario is the identification of the amorphous substance that stained red with congo-red dye during the biopsy. In the context of amyloidosis, the congo-red stain is significant because it binds to amyloid fibrils, which appear as apple-green birefringent deposits under polarized light.

This staining characteristic is a hallmark of amyloid deposits found in various tissues, leading to the systemic effects seen in patients, such as neuropathy and organ dysfunction, including renal impairment. The presence of these symptoms in a diabetic patient also aligns with the common association between diabetes and secondary amyloidosis, particularly from the accumulation of amyloid A protein resulting from chronic inflammation or conditions such as rheumatoid arthritis or chronic infections.

Other potential diagnoses presented do not fit this clinical picture. For instance, diabetic retinopathy primarily affects the eyes and would not typically present with the described renal findings. Sarcoidosis can cause granulomatous inflammation but does not typically exhibit congo-red staining. Glycogen storage diseases are related to enzymatic defects in glycogen