Fig.20.32 ).Themicroaneurysmsarediscretesacculardilationsofretinalchoroidalcapillariesthatappearthroughtheophthalmoscopeassmallreddots.Dilationstendtooccuratfocalpointsofweakening,resultingfromlossofpericytes.Retinaledemapresumablyresultsfromexcessivecapillarypermeability.Underlyingallofthesechangesisthemicroangiopathy,whichisthoughttoleadtolossofcapillarypericytesandhencetofocalweakeningofcapillarystructure.
Theso-calledproliferativeretinopathyisaprocessofneovascularizationandfibrosis.Thislesionleadstoseriousconsequences,includingblindness,especiallyifitinvolvesthemacula.Vitreoushemorrhagesmayresultfromtheruptureofnewlyformedcapillaries;thesubsequentorganizationofthehemorrhagecanpulltheretinaoffitssubstratum(retinaldetachment).
Diabeticneuropathy.Thecentralandperipheralnervoussystemsarenotsparedbydiabetes.Themostfrequentpatternofinvolvementisthatofaperipheral,symmetricneuropathyofthelowerextremitiesaffectingbothmotorandsensoryfunction,particularlythelatter.Otherformsincludeautonomicneuropathy,whichproducesdisturbancesinbowelandbladderfunctionandsometimessexualimpotence,anddiabeticmononeuropathy,whichmaymanifestassuddenfootdroporwristdroporisolatedcranialnervepalsies.Theneurologicchangesmaybetheresultofmicroangiopathyandincreasedpermeabilityofthecapillariesthatsupplythenerves,aswellasdirectaxonaldamage.
Clinical Features of Chronic Diabetes
As the previous discussion has emphasized, type 1 and type 2 diabetes are distinct pathophysiologic entities with the common manifestation of hyperglycemia.
Table 20.6 summarizes some of the clinical, genetic and histopathologic features that distinguish the two diseases. Nonetheless, as previously stated, the long-term sequela of both types 1 and 2 diabetes, arising as a result of uncontrolled
Table20.6Type1VersusType2DiabetesMellitus
Betacelldepletion,isletMildbetacelldepletionatrophy
HLA, Humanleukocyteantigen;MHC, majorhistocompatibilitycomplex.
http://ebooksmedicine.net or poorly controlled hyperglycemia, are similar, and are responsible for much of the morbidity and mortality in diabetics. In most instances these complications appear approximately 15 to 20 years after the onset of hyperglycemia. The major chronic complications of the disease are described next.
Macrovascular complications, such as myocardial infarction, renal vascular insufficiency, and cerebrovascular accidents, are the most common causes of mortality in long-standing diabetes. Diabetics have a two to four times greater incidence of coronary artery disease, and a fourfold higher risk of death from cardiovascular complications, than nondiabetics. Diabetes is often accompanied by underlying conditions that favor the development of adverse cardiovascular events, including hypertension and dyslipidemia (see earlier discussion on metabolic syndrome). The hallmark of cardiovascular disease is accelerated atherosclerosis of the large-and medium-sized arteries (i.e., macrovascular disease). The importance of obesity in the pathogenesis of insulin resistance has already been discussed, but it also is an independent risk factor for development of atherosclerosis.