The late complications of diabetes mellitus.

Late complications of diabetes mellitus include a variety of clinical pictures, mainly related to the involvement of the arterial wall both of large vessels (macroangiopathy) and small vessels (microangiopathy), and of the peripheral nervous system (neuropathy). Their presence in almost all types of diabetes indicates that there is a common pathogenetic mechanism, which can be substantially identified in high blood glucose levels and related alterations. Hyperglycemia, in fact, leads to some metabolic abnormalities, i.e. non-enzymatic glycosylation of proteins and polyol pathway activity; moreover it can negatively affect the pattern of some hormones, especially GH and sex steroids, and normal rheological and clotting properties of blood. These abnormalities, confirmed by experimental models, play a key role in the development of late diabetic complications. However some evidence indicates that a genetic background may predispose to their development or protect from their onset. The two main forms of diabetic retinopathy, non-proliferative and proliferative, show an incidence which increases with age and duration of diabetes, reaching 100% when diabetes lasts for more than 20 years. The risk of blindness, which is very high for the proliferative form, has been dramatically reduced by laser-photocoagulation. Diabetic nephropathy affects a lesser number of diabetics but, after a silent or preclinical stage, leads to renal failure and subsequent replacement therapy. Strict metabolic control in the silent stage and later rigid anti-hypertensive treatment can prevent or retard the evolution of this complication. A close association has been observed between diabetes and hypertension, which can directly affect the onset and evolution of diabetic nephropathy, probably through a common genetic mechanism. Diabetic neuropathy has a wide variety of clinical manifestations, at somatic, autonomic and central levels and can greatly modify the quality and expectancy of life. However, the major cause of death in diabetic subjects is large vessel disease or macroangiopathy, which is similar to non-diabetic atherosclerosis regarding the main histopathological and clinical manifestations but has a much higher prevalence and severity. Finally, a specific cardiomyopathy has also been described in diabetes mellitus and can account for the high rate of heart failure observed in these patients.