Proximal renal tubular acidosis

Proximal RTA (pRTA) is caused by a failure of the proximal tubular cells to reabsorb filtered bicarbonate from the urine, leading to urinary bicarbonate wasting and subsequent acidemia. The distal intercalated cells function normally, so the acidemia is less severe than dRTA and the urine can acidify to a pH of less than 5.3.^[1] pRTA also has several causes, and may occasionally be present as a solitary defect, but is usually associated with a more generalised dysfunction of the proximal tubular cells called Fanconi's syndrome where there is also phosphaturia, glycosuria, aminoaciduria, uricosuria and tubular proteinuria. The principal feature of Fanconi's syndrome is bone demineralization (osteomalacia or rickets) due to phosphate wasting.

Causes

Familial disorders

• Cystinosis^[2]
• Galactosemia^[3]
• Glycogen storage disease (type I)^[4]
• Hereditary fructose intolerance^[5]
• Lowe syndrome^[6]
• Tyrosinemia
• Wilson's disease^[7]

Acquired disorders

• Amyloidosis^[8]
• Multiple myeloma^[9]
• Paroxysmal nocturnal hemoglobinuria^[10]
• Toxins, such as HAART, ifosfamide,^[11] lead, and cadmium

Treatment

Again this depends on oral bicarbonate supplementation. However, this will increase urinary bicarbonate wasting and may well promote a bicarbonate diuresis. The amount of bicarbonate given may have to be very large, to stay ahead of the urinary losses. Correction with oral bicarbonate may exacerbate urinary potassium losses and precipitate hypokalemia.^[12] As with dRTA, reversal of the chronic acidosis should reverse bone demineralization.^[13]

thiazide diuretics can also be used as treatment by making use of contraction alkalosis caused by them.

References