Proximal renal tubular acidosis

Proximal renal tubular acidosis
SpecialtyNephrology

Proximal renal tubular acidosis (pRTA) or type 2 renal tubular acidosis (RTA) is a type of RTA 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 syndrome where there is also phosphaturia, glycosuria, aminoaciduria, uricosuria and tubular proteinuria.

Patients with type 2 RTA are also typically hypokalemic due to a combination of secondary hyperaldosteronism, and potassium urinary losses - though serum potassium levels may be falsely elevated because of acidosis. Administration of bicarbonate prior to potassium supplementation might lead to worsened hypokalemia, as potassium shifts intracellularly with alkalinization.

The principal feature of Fanconi syndrome is bone demineralization (osteomalacia or rickets) due to phosphate and vitamin D wasting.

Signs and symptoms

In terms of the clinical presentation of proximal RTA we find the following:[2]

Causes

Etiologies of proximal RTA may be divided into primary, isolated causes and secondary causes, or those related to another disease.[3] Primary causes are frequently single gene hereditary disorders. Secondary disorders can be divided into familial disorders, acquired disorders, and those related to other clinical entities.

Primary Disorders

  • Autosomal dominant
  • Autosomal Recessive with Ocular Abnormalities (caused by SLC4A4 mutation)
  • Sporadic of Infancy (possibly related to immaturity of NHE-3)

Secondary Disorders

Familial disorders

Acquired disorders

Diagnosis

Differences in urinary pH and plasma bicarbonate in proximal and distal RTA

Diagnosis of proximal renal tubular acidosis is done by measuring the level of fractional excretion of bicarbonate in the urine. Since in proximal renal tubular acidosis patients the nephron is unable to reabsorb bicarbonate, the level of bicarbonate is going to be high in the urine.

Treatment

Treatment consists of 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.[14] As with dRTA, reversal of the chronic acidosis should reverse bone demineralization.[15]

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

See also

References

  1. ↑ Rodriguez Soriano J, Boichis H, Stark H, Edelmann CM (1967). "Proximal renal tubular acidosis. A defect in bicarbonate reabsorption with normal urinary acidification". Pediatr. Res. 1 (2): 81–98. doi:10.1203/00006450-196703000-00001. PMID 6029811.
  2. ↑ "Proximal renal tubular acidosis: MedlinePlus Medical Encyclopedia". medlineplus.gov. Archived from the original on 7 October 2021. Retrieved 20 May 2022.
  3. ↑ Soriano, Juan Rodríguez (2002-08-01). "Renal Tubular Acidosis: The Clinical Entity". Journal of the American Society of Nephrology. 13 (8): 2160–2170. doi:10.1097/01.ASN.0000023430.92674.E5. ISSN 1046-6673. PMID 12138150. Archived from the original on 2022-04-07. Retrieved 2022-04-19.
  4. ↑ Gahl WA, Thoene JG, Schneider JA (2002). "Cystinosis". N. Engl. J. Med. 347 (2): 111–21. doi:10.1056/NEJMra020552. PMID 12110740.
  5. ↑ Golberg L, Holzel A, Komrower GM, Schwarz V (1956). "A clinical and biochemical study of galactosaemia; a possible explanation of the nature of the biochemical lesion". Arch. Dis. Child. 31 (158): 254–64. doi:10.1136/adc.31.158.254. PMC 2011923. PMID 13363463.
  6. ↑ Matsuo N, Tsuchiya Y, Cho H, Nagai T, Tsuji A (1986). "Proximal renal tubular acidosis in a child with type 1 glycogen storage disease". Acta Paediatr Scand. 75 (2): 332–5. doi:10.1111/j.1651-2227.1986.tb10210.x. PMID 3457521.
  7. ↑ Morris RC (1968). "An experimental renal acidification defect in patients with hereditary fructose intolerance. I. Its resemblance to renal tubular acidosis". J. Clin. Invest. 47 (6): 1389–98. doi:10.1172/JCI105830. PMC 297294. PMID 5653216.
  8. ↑ Hodgson SV, Heckmatt JZ, Hughes E, Crolla JA, Dubowitz V, Bobrow M (1986). "A balanced de novo X/autosome translocation in a girl with manifestations of Lowe syndrome". Am. J. Med. Genet. 23 (3): 837–47. doi:10.1002/ajmg.1320230311. PMID 3953680.
  9. ↑ Weibers, DO; Wilson, DM; McLeod, RA; Goldstein, NP (August 1979). "Renal stones in Wilson's disease". Am J Med. 67 (2): 249–54. doi:10.1016/0002-9343(79)90399-1. PMID 463930. Archived from the original on 2012-09-04.
  10. ↑ Rochman, J; Lichtig, C; Osterweill, D; Tatarsky, I; Eidelman, S (October 1980). "Adult Fanconi's syndrome with renal tubular acidosis in association with renal amyloidosis: occurrence in a patient with chronic lymphocytic leukemia". Arch Intern Med. 140 (10): 1361–3. doi:10.1001/archinte.140.10.1361. PMID 6775610. Archived from the original on 2012-04-05. Retrieved 2022-04-19.
  11. ↑ Messiaen T, Deret S, Mougenot B, et al. (2000). "Adult Fanconi syndrome secondary to light chain gammopathy. Clinicopathologic heterogeneity and unusual features in 11 patients". Medicine (Baltimore). 79 (3): 135–54. doi:10.1097/00005792-200005000-00002. PMID 10844934.
  12. ↑ Riley AL, Ryan LM, Roth DA (1977). "Renal proximal tubular dysfunction and paroxysmal nocturnal hemoglobinuria". Am. J. Med. 62 (1): 125–9. doi:10.1016/0002-9343(77)90357-6. PMID 13653.
  13. ↑ Skinner R (2003). "Chronic ifosfamide nephrotoxicity in children". Med. Pediatr. Oncol. 41 (3): 190–7. doi:10.1002/mpo.10336. PMID 12868118.
  14. ↑ Rodríguez Soriano J (2002). "Renal tubular acidosis: the clinical entity". J. Am. Soc. Nephrol. 13 (8): 2160–70. doi:10.1097/01.ASN.0000023430.92674.E5. PMID 12138150. Archived from the original on 2021-08-29. Retrieved 2022-04-19.
  15. ↑ McSherry E (1981). "Renal tubular acidosis in childhood". Kidney Int. 20 (6): 799–809. doi:10.1038/ki.1981.213. PMID 7038264.
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