What common infections cause chronic tubulointerstitial nephritis?
• Chronic pyelonephritis
• Chronic bacterial infections of the urinary tract are among the most common causes of chronic tubulointerstitial nephritis. The majority of these cases are associated with vesicoureteral reflux (VUR)—hence the term “reflux nephropathy . ” For those not associated with VUR, however, the disease is termed “chronic pyelonephritis.”
• Clinically, patients with chronic pyelonephritis present with symptoms consisting of fever and chills, dysuria, vague flank or back pain, and hypertension. Some patients may present with tubular abnormalities, such as impaired urinary concentrating ability, hyperkalemia, and salt wasting, all of which reflect distal tubular dysfunction. Chronic or repeated urinary tract infections are predisposing risk factors.
• Examination of the urine often reveals an active urinary sediment consisting of WBCs and WBC casts.
• Grossly, the kidneys may appear contracted.
• Histopathologically, findings are similar to other forms of chronic tubulointerstitial nephritis, with tubular atrophy and interstitial fibrosis. Lymphocytes and mononuclear cells predominate the chronic inflammatory infiltrative population.
• Xanthogranulomatous pyelonephritis
• Persistent chronic pyelonephritis can progress to a localized infection called “xanthogranulomatous pyelonephritis.” Typically, this is associated with urinary tract obstruction. There is ischemia and destruction of kidney parenchymal tissue, granuloma formation, and subsequent accumulation of lipid deposits. These lipid deposits are actually lipid-laden macrophages called foam cells.
• Symptoms are similar to those of chronic pyelonephritis. Characteristically, a distinct mass may be palpable over the affected “nonfunctioning” kidney.
• Urine cultures are usually positive for E. coli , other gram-negative bacilli or Staphylococcus aureus .
• Computed tomography, the imaging modality of choice, may show the source of obstruction (stone), an enlarged kidney, and dilated calyces. Neoplasm must be excluded.
• On intravenous pyelography, the involved kidney may contain a localized abscess-like area, which may look like a complex cyst or tumor.
• Current treatment recommendations consist of antibiotic therapy combined with total or partial nephrectomy.
