Distal renal tubular acidosis

Distal renal tubular acidosis (dRTA) is the classical form of RTA, being the first described. Distal RTA is characterized by a failure of acid secretion by the

• Normal anion gap metabolic acidosis/acidemia
• Hypokalemia
• Urinary stone formation (related to alkaline urine, hypercalciuria, and low urinary citrate).^[3]
• Nephrocalcinosis (deposition of calcium in the substance of the kidney)
• Bone demineralisation (causing rickets in children and osteomalacia in adults)

The symptoms and sequelae of dRTA are variable and range from being completely

dRTA commonly leads to sodium loss and volume contraction, which causes a compensatory increase in blood levels of aldosterone.^[4] Aldosterone causes increased resorption of sodium and loss of potassium in the collecting duct of the kidney, so these increased aldosterone levels cause the hypokalemia which is a common symptom of dRTA.^[4]

Causes

• systemic lupus erythematosus, rheumatoid arthritis and even hypergammaglobulinemia. Hypokalaemia is often severe in these cases.^[5]
• Hereditary causes include mutations of
  apical proton pump vH⁺-ATPase,^[8] which are transmitted in an autosomal recessive fashion, and may be associated with sensorineural deafness.^[9]
• Liver cirrhosis.
• cortical collecting duct
  .
• Renal transplantation
  .
• Sickle cell anemia
  .
• Toxins, including ifosfamide (more commonly causing pRTA than dRTA),^[10] lithium carbonate^[11] and amphotericin B.^[12]
• Chronic urinary tract obstruction.
• Toluene causes a non-anion gap metabolic acidosis with hypokalemia and a positive urinary anion gap that looks a lot like distal RTA but there is no hydrogen secretion defect and the acidosis is due to acid production during the metabolism of toluene.^[13]

Diagnosis

The pH of patient's blood is highly variable, and acidemia is not necessarily characteristic of people with dRTA at any given time. One may have dRTA caused by

dRTA has been proposed as a possible diagnosis for the unknown malady plaguing Tiny Tim in Charles Dickens' A Christmas Carol.^[17][18]

Treatment

This is relatively straightforward. It involves correction of the acidemia with oral sodium bicarbonate, sodium citrate or potassium citrate. This will correct the acidemia and reverse bone demineralisation. Hypokalemia and urinary stone formation and nephrocalcinosis can be treated with potassium citrate tablets which not only replace potassium but also inhibit calcium excretion and thus do not exacerbate stone disease as sodium bicarbonate or citrate may do.^[19]

See also

• Renal tubular acidosis
• Proximal renal tubular acidosis
• Ifosfamide

References