True polyuria and polydipsia are symptoms frequently encountered in clinical medicine. Generally they indicate a serious organic disorder which must be systematically investigated for prompt and adequate diagnosis. Table 1 represents a schematic presentation of the major polyuric syn- dromes. In all instances the symptom arises whenever there is a decrease in the per cent of the water normally reabsorbed from the glomerular filtrate. As can be seen, this results from (1) a decrease in the reabsorption of water per se, (2) a decrease in the reabsorption of solutes, with, therefore, an obligatory excretion of water (absolute or relative osmotic diuresis*), or (3) a combination of one and two.
Recently a case was observed which, while classifiable, presented features which to our knowledge had not been previously described. This patient, an example of long-standing psychogenic polydipsia, was initially unable to concentrate his urine above the osmolality of his extracellular fluid,
KLEEMAN CR, MAXWELL MH, WITLIN S. Functional Isosthenuria: An Isolated Reversible Renal Tubular Defect. AMA Arch Intern Med. 1958;101(6):1023–1028. doi:10.1001/archinte.1958.00260180013002
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