Nephrosis: Any degenerative disease of the kidney tubules, the tiny canals that make up much of the substance of the kidney. Nephrosis can be caused by kidney disease, or it may be a complication of another disorder, particularly diabetes. Diagnosis is made via urine testing for the presence of protein, blood testing for lower-than-normal levels of protein, and observation of edema. Treatment usually involves use of cortisone-like drugs. Also known as nephrotic syndrome.