Prophylaxis and methods for early recognition of aluminium intoxication

Dementia in patients undergoing long-term dialysis: aetiology, differential diagnoses, epidemiology and management

Dementia in patients undergoing long-term dialysis has not been clearly defined; however, four different entities have been described. Uraemic encephalopathy is a complication of uraemia and responds well to dialysis. Dialysis encephalopathy syndrome, the result of acute intoxication of aluminium caused by the use of an aluminium-containing dialysate, was a common occurrence prior to 1980. However, using modern techniques of water purification, such acute intoxication can now be avoided. Dialysis-associated encephalopathy/dementia (DAE) is always associated with elevated serum aluminium levels. Pathognomonic morphological changes in the brain have been described, but the mechanism for the entry of aluminium into the CNS is incompletely understood. The mechanisms involved in the pathogenesis of the neurotoxicity associated with aluminium are numerous. Although only a very small fraction of ingested aluminium is absorbed, the continuous oral aluminium intake from aluminium-based phosphate binders, and also of dietary or environmental origin, is responsible for aluminium overload in dialysis patients. Age-related dementia, especially vascular dementia, occurs in patients undergoing long-term dialysis as frequently as it does in the general population. The differential diagnoses of dialysis-associated dementias should include investigation for metabolic encephalopathies, heavy metal or trace element intoxications, and distinct structural neurological lesions such as subdural haematoma, normal pressure hydrocephalus, stroke and, particularly, hypertensive encephalopathy and multi-infarct dementia. To prevent DAE, dietary training programmes should aim to achieve the lowest phosphate intake and pharmacological tools should be used to keep serum phosphate levels below 2 mmol/L. To prevent vascular dementia, lifestyle modification should be undertaken, including optimal physical activity and fat intake, nicotine abstinence, and targeting optimal blood glucose, cholesterol and triglyceride levels, and blood pressure, to those outlined in current recommendations.

Recent developments in aluminum toxicology

Aluminum is now recognised as an important toxin causing considerable morbidity and mortality, particularly in patients with chronic renal failure. Diseases that have been associated with aluminium include dialysis dementia, renal osteodystrophy and Alzheimer's disease. Aluminum also has an effect on red blood cells, parathyroid glands and chromosomes. Accumulation of aluminium in the body tends to occur when the gastrointestinal barrier is circumvented. This has been identified as a problem during dialysis or intravenous fluid administration. Renal functional impairment results in decreased aluminum excretion and promotes accumulation of the element in the body. Many sources have been shown to be contaminated with aluminium. These include the water used for dialysis; medicines containing aluminium, such as aluminium-containing phosphate binding gels; total parenteral nutrition solutions; processed human serum albumin; intravenous fluids in infants; and other environmental and industrial sources. The management of aluminium toxicity involves the identification of these contaminated sources and subsequent removal of the element. This includes regular monitoring of water used in dialysis. The use of aluminium-containing phosphate binding gels in patients with compromised renal function should be reviewed and alternatives sought. The development of effective aluminium-free phosphate binders is desirable. Once a patient has aluminium toxicity, desferrioxamine (deferoxamine) has been shown to be an effective agent in its chelation and removal.

Renal osteodystrophy

Over the past decade important advances in our understanding of the pathophysiology and treatment of renal osteodystrophy have been made. In particular, the role of calcitriol deficiency in the genesis of hyperparathyroidism in early renal failure is now better understood. So too are the effects of aluminium on bone, and whereas the more florid aluminium related disease is now unusual the more subtle effects of aluminium are now being appreciated. There is still a major problem in the long-term treatment of hyperparathyroid bone disease. The reasons why parathyroid gland proliferation continues to occur on dialysis therapy require a better understanding of cellular events regulating hormone production and parathyroid cell replication. The case for early intervention with vitamin D is now strong but whether such an approach materially influences the long-term outcome is not yet established. Changes in the approach to treatment and in the modalities used for renal replacement therapy will continue to modify the nature of the bone disease.

Renal effects of aluminium in uraemic rats and in rats with intact kidney function

The effect on renal function following administration of aluminium (i.p., five times weekly (0.05 or 0.5 mg kg-1 body weight) for 12 weeks) to partially nephrectomized (5/6 NX) or intact female rats was examined. The observed loss of concentrating ability, characterized by increased urine volume and an increased sodium excretion, as well as increased renal excretion of p-aminohippurate (demonstrable after low-dose treatment with nephrotoxins) can be interpreted as an initiation of kidney function injury. No distinct differences in response were observed between partially nephrectomized and intact animals.