Kidney. Amyloidosisofthekidneyisthemostcommonandpotentiallythemostseriousformoforganinvolvement.Grossly,thekidneysmaybeofnormalsizeandcolor,orinadvancedcasestheymaybeshrunkenbecauseofischemiacausedbyvascularnarrowinginducedbythedepositionofamyloidwithinarterialandarteriolarwalls.Histologically,theamyloidisdepositedprimarilyintheglomeruli,buttheinterstitialperitubulartissue,arteries,andarteriolesarealsoaffected.Theglomerulardepositsfirstappearassubtlethickeningsofthemesangialmatrix,accompaniedusuallybyunevenwideningofthebasementmembranesoftheglomerularcapillaries.Intime,depositsinthemesangiumandalongthebasementmembranescausecapillarynarrowinganddistortionoftheglomerularvasculartuft.Withprogressionoftheglomerularamyloidosis,thecapillarylumensareobliteratedandtheobsolescentglomerulusisreplacedbyconfluentmassesorinterlacingbroadribbonsofamyloid.
Spleen. Amyloidosisofthespleenmaybeinapparentgrosslyormaycausemoderatetomarkedsplenomegaly(upto800g).Formysteriousreasons,twodistinctpatternsofdepositionareseen.Inone,thedepositsarelargelylimitedtothesplenicfollicles,producingtapioca-likegranulesongrossinspection,designatedsago spleen. Intheotherpattern,theamyloidinvolvesthewallsofthesplenicsinusesandconnectivetissueframeworkintheredpulp.Fusionoftheearlydepositsgivesrisetolarge,maplikeareasofamyloidosis,creatingwhathasbeendesignatedlardaceous spleen.
Liver. Thedepositsmaybeinapparentgrosslyormaycausemoderatetomarkedhepatomegaly.AmyloidappearsfirstinthespaceofDisseandthenprogressivelyencroachesonadjacenthepaticparenchymalcellsandsinusoids.Intime,deformity,pressureatrophy,anddisappearanceofhepatocytesoccur,causingtotalreplacementoflargeareasofliverparenchyma.VascularinvolvementanddepositsinKupffercellsarefrequent.Liverfunctionisusuallypreserveddespitesometimesquiteextensiveinvolvement.
Heart. Amyloidosisoftheheart(Chapter11)mayoccurinanyformofsystemicamyloidosis.Italsoisthemajororganinvolvedinsenilesystemicamyloidosis.Theheartmaybeenlargedandfirm,butmoreoftenitshowsnoappreciablechangeongrossinspection.Histologicallythedepositsbeginasfocalsubendocardialaccumulationsandwithinthemyocardiumbetweenthemusclefibers.Expansionofthesemyocardialdepositseventuallycausespressureatrophyofmyocardialfibers.Whentheamyloiddepositsaresubendocardial,theconductionsystemmaybedamaged,accountingfortheelectrocardiographicabnormalitiesnotedinsomepatients.
Other Organs. Nodulardepositionsinthetongue maycausemacroglossia,givingrisetothedesignationtumor-formingamyloidofthetongue.Therespiratory tract maybeinvolvedfocallyordiffuselyfromthelarynxdowntothesmallestbronchioles.Adistinctformofamyloidisfoundinthebrains ofpatientswithAlzheimerdisease.Itmaybepresentinso-called“plaques”aswellasbloodvessels(Chapter23).Amyloidosisofperipheralandautonomicnerves isafeatureofseveralfamilialamyloidoticneuropathies.