The present knowledge of the state of the microvasculature in diabetic subjects early during the course of the disease and prior to any clinical signs of retinopathy and nephropathy is reviewed. Functional changes in the peripheral vascular bed have been demonstrated by various methods in the retina, the skin and the conjunctiva. The common features of these functional changes appear to be a loss of normal vascular tone and increased permeability. There is also evidence of a functional disorder of the glomerular capillaries in young diabetics early during their disease, as indicated by increased glomerular filtration rates.
Based on the presence of a functional microangiopathy, a dynamic concept of the development of clinical microangiopathy is presented. It is suggested that the functional changes may occur very early and might in some instances come before the degenerative vascular changes. Thus they might participate in the mechanism of the development of the long-term diabetic syndrome.