Pathogenesis of Cerebral Atrophy in Uraemia

Abstract

This paper discusses the possible pathogenesis of the cerebral atrophy (CA) observed in a large percentage of uraemic patients, taking the form of prevalently cortical damage (cortical atrophy) and/or subcortical enlargement of ventricular cavities (subcortical atrophy). This central nervous system pathology seems to share very little either with the better known ‘dialysis encephalopathy’ or with the ‘acute encephalopathy syndrome’, even though sporadic cases of both these forms have shown concomitant CA. Histopathologically it offers the picture of loss of neurons and nerve fibres and can thus be compared with uraemic peripheral nervous system damage. CA is unquestionably important because of its implications in terms of impairment of superior cortical functions, just as in CA of non-uraemic aetiology. A first aetiopathogenic hypothesis might include endogenous uraemic intoxication to the nerve tissue, believed responsible for peripheral uraemic neuropathy, but other possibilities merit consideration: vascular calcification secondary to hyperparathyroidism, blood lipid disorders, and systemic hypertension – factors that contribute to impairing the brain vasculature, with cascade effects on brain tissue oxygenation, neuronal metabolism, and energy exchanges. Tissue oxygenation is already jeopardized in the uraemic patient by the concomitant chronic anaemia and by cardiac insufficiency in cases with hypertensive heart disease. In dialysis patients with volume-dependent hypertension the brain may be further damaged by abrupt pressure changes produced by dialytic ultrafiltration; these constitute a severe challenge to cerebral blood flow autoregulation. Cyclic variations of brain tissue hydration connected with regular dialysis treatment may have adverse effects on neurotransmitter functions, particularly those mediated by neuropeptidergic systems. Chronic intoxication may result from oral A1(OH)₃ of phosphorus-chelating agents: in animal studies and clinical observations in non-uraemic populations the neurotoxic potential of A1 is indicated by a significant correlation between histological neuronal damage, impaired function, and A1 concentration in brain tissues. In addition, a concausal role of malnutrition in central nervous system damage in the uraemic patient cannot be overlooked, since malnutrition is known to give rise to functional and structural alterations in non-uraemic human pathology. In the light of these clinical observations and experimental findings, it would appear that the prevention of CA in uraemia is today feasible.