[Classification and diagnosis of proximal renal tubular acidosis].
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Our aim in this article is to propose a new hypothesis concerning the etiology of renal tubular acidosis (RTA) in that subgroup of patients who have the isolated, primary type of proximal RTA. We suggest that their underlying disorder is a more alkaline intracellular pH of the proximal convoluted tubule. Increased alkalinity of proximal tubular cells would explain the low rate of bicarbonate reabsorption per liter glomerular filtration and the decreased rate of ammonium excretion despite a low urine pH and the presence of chronic metabolic acidosis. Additional diagnostic tests to evaluate this hypothesis in this specific subgroup of patients with proximal RTA are also outlined.
While distrubances of the acid-base balance are frequently seen in infancy, renal tubular acidosis is a rather rare disease but should be considered as differential diagnosis if metabolic acidosis persists after adequate treatment. Proximal and distal tubular acidosis with primary and secondary forms can be differentiated. Proximal RTA is characterized by the loss of bicarbonate, distal RTA by a defect to establish a hydrogen ion gradient and thus to accomplish acidification of urine. In addition to these two basic forms a bicarbonate wasting state in distal RTA has been described. A patient with these clinical features is presented. He was admitted to our hospital at the age of 1 month with meningitis, enteritis and marked dystrophy. A persistant hyperchloraemic acidosis with concomitant hypokalaemia was present. The ammonium chloride loading test confirmed the diagnosis of primary distal RTA. Renal biopsy performed with 1 year of age revealed nephrocalcinosis of the inner medullary region of the kidney while the cortex was not affected. The patient first needed alkali doses of 12 mEq/kg/day which could be gradually reduced to 3.5 mEq/kg/day. Under additional potassium substitution of 5 mEq/kg/day he was thriving well. Differential diagnosis and the particular clinical features of this case are discussed.
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An infant girl presented with recurrent episodes of Reye-like syndrome associated with hypoketosis and plasma carnitine levels in the high-normal range. A liver biopsy revealed massive macrovesicular steatosis. Ketogenesis was absent after a long-chain triglyceride loading test; in contrast, the medium-chain triglyceride loading test resulted in a brisk rise in plasma ketone concentration. Carnitine palmitoyltransferase I deficiency was demonstrated in cultured skin fibroblasts. Hypoglycemia was only found once in the neonatal period. Renal carnitine handling was normal except for a higher renal threshold for free carnitine. Mild, persistent metabolic acidosis was a constant feature, even during periods between metabolic decompensation. Evaluation of the renal acidification capacity showed a failure to acidify the urine during spontaneous acidosis but increased acid excretion and a normal decrease of urinary pH after acid loading. Also, a small difference between urine and blood PCO2 was found after bicarbonate administration. This acidification defect can best be explained as an abnormality in distal tubular H+ secretion: a rate-dependent distal tubular acidosis.off is speculated that long-chain acylcarnitines, substances that cannot be formed by carnitine palmitoyltransferase I-deficient patients, play an essential role in renal acid-base homeostasis.
Spironolactone therapy is a well-known cause of hyperkalaemia, but in susceptible patient, it may also be associated with metabolic acidosis. We report a case of severe renal tubular acidosis (Type IV) with life-threatening hyperkalaemia caused by spironolactone, and discuss the mechanisms by which this may occur.
We report a patient with metastatic non-small cell lung cancer who developed renal toxicities manifest as acute renal failure associated with nephrogenic diabetes insipidus and distal renal tubular acidosis following sequential therapy with pemetrexed. The nephrotoxicity occurred concomitantly with severe myelosuppression. We postulate renal tubular toxicity may account for distinct patterns of injury including acute renal failure and tubular cell dysfunction of the distal nephron.
A four-year-old castrated male domestic shorthair cat with recent onset of lethargy and depression was found to have hypokalaemia, low plasma bicarbonate concentration and a urine pH of 7. Subsequent findings of hyperchloraemic metabolic acidosis with failure to produce acid urine led to a diagnosis of distal renal tubular acidosis. Pyelonephritis associated with Escherichia coli infection of the urinary tract was also diagnosed. The urinary tract infection was eliminated by antibiotic treatment. For two years subsequently, the clinical effects of distal renal tubular acidosis have been controlled by oral administration of potassium bicarbonate, although some biochemical abnormalities have persisted.