Tubulointerstitial Disorders



Tubulointerstitial Disorders







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Renal disorders that affect the proximal and distal tubules and sometimes the tissue surrounding the tubules are termed tubulointerstitial disorders. These disorders, which include renal tubular acidosis, pyelonephritis, and drug-related nephropathies, may be acute or chronic in nature. Acute disease produces an abrupt onset of signs and symptoms, whereas chronic disorders result in fibrosis and atrophy of nephrons. Early signs of tubulointerstitial disorders include signs and symptoms of fluid and electrolyte imbalance such as nocturia, polyuria, and metabolic acidosis.






RENAL TUBULAR ACIDOSIS


Pathophysiology

Proximal tubular defects hinder bicarbonate reabsorption, whereas distal tubular defects result in a reduction of the secretion of metabolic acids. Both lead to metabolic acidosis, bone disease, renal calculi, and growth retardation in children.



image Early signs of tubulointerstitial disorders include signs and symptoms of fluid and electrolyte imbalance such as nocturia, polyuria, and metabolic acidosis.

Because the proximal tubules are where 90% to 95% of filtered bicarbonate is reabsorbed, defects affecting this area result in a loss of bicarbonate and sodium into the urine. Associated with the loss of bicarbonate and sodium is a reduction of serum bicarbonate levels, hypovolemia, increased aldosterone secretion, and hypokalemia. The distal tubules
continue to function and excrete metabolic acids. Eventually, the proximal tubules regain enough function to reabsorb a small amount of bicarbonate.








Table 64-1 Types of Renal Tubular Acidosis





















Type

Characteristics

Etiology


Type I (classic distal renal tubular acidosis)



  • Selective deficiency in hydrogen ion secretion of cells in the collecting tubules



  • Autoimmune disease



  • Drugs/toxins, i.e., amphotericin B


Type II (proximal renal tubular acidosis)


  • Hypokalemic hyperchloremic metabolic acidosis



  • Bicarbonate is not reabsorbed by the proximal tubule



  • Distal nephron tries to reabsorb some bicarbonate but becomes overwhelmed by the bicarbonate load and does not function adequately



  • As bicarbonate is lost in the urine, the serum bicarbonate level falls and the distal nephron can again reabsorb some bicarbonate


  • Selective defects in the proximal tubule inhibit reabsorption of bicarbonate



  • May be caused by carbonic anhydrase inhibitors



  • Multiple myeloma



  • Nephrotoxic drugs


Type IV* (hyporeninemic [low levels of renin in plasma] hypoaldosteronemic renal tubular acidosis)



  • Aldosterone deficiency— impairs distal nephron sodium reabsorption and potassium and hydrogen ion excretion



  • Diabetic nephropathy



  • Hypertensive nephrosclerosis



  • Acquired immunodeficiency syndrome


* A type III does not exist.

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Oct 21, 2016 | Posted by in NURSING | Comments Off on Tubulointerstitial Disorders

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