Clinical Presentation



Dysfunction of the renal tubules can have myr­iad clinical manifestations, reflecting the many regulatory functions of the different nephron seg­ments. Tubular disorders may present as altera­tions in osmotic balance (nephrogenic diabetes in­sipidus), in acid-base regulation (renal tubular acidosis), in extracellular fluid volume homeo­stasis (salt-losing nephropathy), and in mineral metabolism (primary phosphaturia). In each case, the function of the segment of the nephron most affected determines the clinical manifestations of the syndrome. Some tubular disorders are purely functional and do not directly affect glomerular filtration. Renal failure, expressed as a reduction in the GFR, occurs only as an indirect effect of altered body homeostasis (see Chapter 29) in these disorders.

Other diseases, however, originate in the tub-ulointerstitial compartment of the kidney and, be­cause of the destructive nature of the lesion, do lead to reductions in GFR. Such disorders include the hereditary cystic diseases of the kidney (po­lycystic kidney disease) and the chronic intersti­tial nephritides (lead nephropathy, analgesic ne­phropathy). The initial presentation of these disorders also reflects the loss of specific tubular functions, and only when far-advanced do they display characteristics of a reduction in GFR. Table 34-4 outlines the diseases discussed in this section.