Acute pyelonephritis often is associated with predisposing conditions, as described earlier in the discussion of pathogenetic mechanisms. After the first year of life (an age by which congenital anomalies in males commonly become evident) and up to approximately 40 years of age, infections are much more frequent in females. Up to 6% of pregnant women develop bacteriuria some time during pregnancy, and 20% to 40% of these eventually develop symptomatic urinary infection if not treated. With increasing age, the incidence in males rises as a result of the development of prostatic hyperplasia, which causes urinary outflow obstruction.
The onset of uncomplicated acute pyelonephritis usually is sudden, with pain at the costovertebral angle and systemic evidence of infection, such as chills, fever, nausea, malaise, and localizing urinary tract signs of dysuria, frequency, and urgency. The urine appears turbid due to the contained pus (pyuria). The disease usually is unilateral, and affected individuals thus do not develop renal failure. In cases in which predisposing factors are present, the disease may become recurrent or chronic and is more likely to be bilateral. The development of papillary necrosis is associated with a much poorer prognosis.
Chronic pyelonephritis is a clinicopathologic entity in which interstitial inflammation and scarring of the renal parenchyma are associated with grossly visible scarring and deformity of the pelvicalyceal system in patients with a history of UTI. Chronic pyelonephritis is an important cause of chronic kidney disease. It can be divided into two forms: chronic obstructive pyelonephritis and chronic reflux–associated pyelonephritis.
As noted, obstruction predisposes the kidney to infection. Recurrent infections superimposed on diffuse or localized obstructive lesions lead to recurrent bouts of renal inflammation and scarring, which eventually cause chronic pyelonephritis. The disease can be bilateral, as with congenital anomalies of the urethra (e.g., posterior urethral valves), or unilateral, such as occurs with calculi and unilateral obstructive lesions of the ureter.
Chronic reflux–associated pyelonephritis is the most common cause of chronic pyelonephritis. It results from superimposition of a UTI on congenital vesicoureteral reflux and intrarenal reflux. Both the reflux and the attendant renal damage may be unilateral or bilateral, the latter potentially leading to chronic renal insufficiency.
MORPHOLOGYOneorbothkidneysmaybeinvolved,eitherdiffuselyorinpatches.Evenwheninvolvementisbilateral,thekidneysarenotequallydamagedandthereforearenotequallycontracted.Thisuneven scarring isusefulindifferentiatingchronicpyelonephritisfromthemoresymmetricallycontractedkidneysassociatedwithvascularsclerosis(oftenreferredtoasbenign nephrosclerosis)andchronicGN.Thehallmarkofchronicpyelonephritisisscarring involving the pelvis or calyces, orboth,leadingtopapillarybluntingandmarkedcalyceal deformities (
Fig.14.14
Themicroscopicchangesarelargelynonspecific,andsimilaralterationsmaybeseenwithotherchronictubulointerstitialdisorderssuchasanalgesicnephropathy.Theparenchymashowsthefollowingfeatures:
Uneveninterstitialfibrosisandaninflammatoryinfiltrateoflymphocytes,plasmacells,andoccasionallyneutrophils