•Acute postinfectious glomerulonephritis typicallyoccursafterstreptococcalinfectioninchildrenandyoungadultsbutmayoccurfollowinginfectionwithmanyotherorganisms.Itiscausedbydepositionofimmunecomplexes,mainlyinthesubepithelialspaces,withabundantneutrophilsandproliferationofglomerularcells.
IgA nephropathy, characterizedbymesangialdepositsofIgAcontainingimmunecomplexes,isthemostcommonformofglomerulonephritisworldwide.Recurrentasymptomatichematuriaisthemostcommonclinicalpresentation.Itcommonlyaffectschildrenandyoungadultsandhasavariablecourse.
Hereditary nephritis (Alport syndrome) iscausedbymutationsingenesencodingGBMcollagen.Itmanifestsashematuriaandslowlyprogressingproteinuriaanddecliningrenalfunction.ThinbasementmembranediseaseisalsocausedbymutationsencodingtheGBMcollagen,however,unlikeAlportsyndrome,thisisusuallyabenignnonprogressivedisorder.
RPGNisaclinicalentitywithfeaturesofthenephriticsyndromeandrapidlossofrenalfunction.
ItiscommonlyassociatedwithsevereglomerularinjurywithnecrosisandGBMbreaksandsubsequentproliferationofparietalepithelium(crescents).
RPGNmaybemediatedbyautoantibodiestotheGBM(anti-GBMantibodydisease),byimmunecomplexdeposition,oritcanbepauci-immuneoftenassociatedwithanti-neutrophilcytoplasmicantibodies(pauci-immuneGN).
Most forms of tubular injury also involve the interstitium, so the two are discussed together. Presented under this heading are diseases characterized by (1) inflammatory involvement of the tubules and interstitium (tubulointerstitial nephritis) and (2) ischemic or toxic tubular injury, leading to acute tubular injury and the clinical syndrome of acute kidney injury.
Tubulointerstitial nephritis (TIN) refers to a group of inflammatory kidney diseases that primarily involve the interstitium and tubules. The glomeruli may be spared altogether or affected only late in the course. In cases of TIN caused by bacterial infection, the renal pelvis is prominently involved—hence the more descriptive term pyelonephritis (from pyelo, “pelvis”). The term interstitial nephritis generally is reserved for cases of TIN that are nonbacterial in origin. These include tubular injury resulting from drugs, metabolic disorders such as hypokalemia, irradiation, viral infections, and immune reactions. On the basis of clinical features and the character of the inflammatory exudate, TIN can be divided into acute and chronic categories. Discussed next is acute pyelonephritis followed by consideration of other forms of interstitial nephritis.
Acute pyelonephritis, a common suppurative inflammation of the kidney and the renal pelvis, is caused by bacterial infection. It is an important manifestation of urinary tract infection (UTI), which can involve the lower (cystitis, prostatitis, urethritis) or upper (pyelonephritis) urinary tract, or both. As we will see, the great majority of cases of pyelonephritis are associated with infections of the lower urinary tract, which are very common. Fortunately, most infections of the lower urinary tract remain localized and do not spread to the kidney.