Inflammatory tubulointerstitial renal diseases - acute and chronic pyelonephritis
Tubulointerstitial nephritis is a group of inflammatory diseases that affect the interstitium and tubules, while the glomeruli may be spared or affected late in the show. Most cases TIN is as a result of bacterial infection and the renal pelvis predominantly involved, as such we call it pyelonephritis, while the term interstitial nephritis usually reserved for conditions that are of non-bacterial origin (including drugs, hypokalemia, radiation, viral infection and immune reactions).
Acute pyelonephritis
A common suppurative inflammation of the kidney and renal pelvis of bacterial etiology, commonly a complication of UTIs. Main etiology are E.coli, Proteus, Klebsiella, Enterobacter and Pseudomonas. Often the result of recurrent UTIs where bacteria ascend up the ureters or travel via the bloodstream (ascending infection the most common). Females are more susceptible due to their shorter urethras, and risk factors are things that decrease bladder voiding (e.g. prostatic hyperplasia). Incompetence of the vesicoureteral orifice can cause vesicoureteral reflux (VUR) which increases risks, this is found in 20-40% of children who get UTIs.
Once the infection reaches the kidneys, we have a problem. The infection can be bi or unilateral, and often makes the kidneys enlarged with yellowish raised abscesses that appear on the renal surface. Histologically we see liquefactive necrosis with formation of
abscesses in the renal parenchyma. Large masses of neutrophils (pus) enter the collecting ducts and can even spread to the renal pelvis, calyces and ureter. A rare complication is that of papillary necrosis of the renal papillae.
Clinical symptoms present with pain of the costovertebral angle and systemic evidence of infection (chills, fever, malaise etc), often with turbid urine.
Remember: white-cell (leukocyte) casts in the urine show that the infection involves the kidney itself and not only the bladder – they form when the neutrophils filling the tubules are moulded into casts. A patient with cystitis alone has pyuria but no white-cell casts.
Chronic pyelonephritis
Chronic pyelonephritis is really a morphologic classification, where we see interstitial inflammation and scarring in the renal parenchyma associated with scarring of the pelvicalyceal system, it is a common form of chronic renal failure. It has two types:
- Chronic obstructive pyelonephritis
- Leads to recurrent bouts of inflammation and scarring
- Chronic reflux-associated pyelonephritis
- More common form, resulting renal damage may cause scarring and atrophy of one or both of the kidneys