Functional aspects of the differential diagnosis of renal disease.

IF we read through both the basic papers which William Bright wrote some 136 and 127 years ago, and which laid the foundations of clinical nephrology, we can recognize in the detailed clinical description the nephrotic syndrome, the effects of severe hypertension and the signs of chronic renal or cardiac insufficiency. These are the endstages which follow almost all types of chronic renal disease, and these late phenomena cannot be used to differentiate between the various morphological entities which the pathologists later constructed from the original tissue of ' Bright's disease '. Such a differentiation was, of course, to no purpose at the period when therapeutic medicine knew little else than venesection, calomel, diaphoretics, suction-cups and a few other drugs which Bright prescribed with both enthusiasm and conviction for his patients. Even in the century following Bright we had little else in our therapeutic armamentarium than a lowprotein, low-salt diet and fluid restriction, so that, again, the differential diagnosis of renal disease was to little avail. The situation in therapy today is quite different, and attempts at differential diagnosis have thereby taken on considerable practical importance. Since morphology of the kidney itself has been the classical criterion of diagnosis, kidney biopsy can be of great assistance, particularly when combined with histochemistry and electron microscopy of the biopsy material. These latter techniques have taught us a great deal of the early stages of kidney disease, since such cases do not come to the postmortem table. It must be stressed, however, that biopsy is not without risk, that it requires the services of a pathologist experienced in interpreting such material, that even in the best of hands about one-quarter of all biopsies ends up with no kidney tissue in the needle, that the biopsy piece may contain so few glomeruli that any interpretation at all is risky, and that one has no guarantee at all that the region of kidney punctured by the needle actually contains the disease