Renal failure is relatively common, but except in association with
spina bifida or
paraplegia it is unlikely to occur as a result of disease of the CNS.
Renal failure, however, commonly affects the nervous system. The effects of
kidney failure on the nervous system are more pronounced when failure is acute. In addition to the important problems related to
renal failure there are both acquired and genetically determined diseases which may affect the kidney and the brain. Those acquired diseases include the
vasculitides, the paraproteinaemias, and various granulomatous conditions (considered in other chapters of Neurology and Medicine). In two of the most commonly encountered genetically determined diseases,
Von Hippel-Lindau disease and
polycystic kidney disease, location of pathogenic mutations will provide improved screening programmes and, possibly, allow therapeutic intervention. Uraemia may affect both the central and peripheral nervous systems. Whereas the clinical features of uraemia are well documented, the pathophysiology is less well understood and probably multifactorial. Uraemic
encephalopathy, which classically fluctuates, is associated with problems in cognition and memory and may progress to
delirium, convulsions, and
coma. The
encephalopathy may initially worsen with periods of dialysis and almost certainly relates to altered metabolic states in association with ionic changes and possibly impaired synaptic function.
Renal failure may affect the peripheral nervous system, resulting in a neuropathy which shows a predilection for large diameter axons. This may be reversed by dialysis and
transplantation. The
myopathy seen in
renal failure, often associated with bone
pain and tenderness, is similar to that encountered in
primary hyperparathyroidism and
osteomalacia. Dialysis itself is associated with neurological syndromes including the
dysequilibrium syndrome, subdural haematoma, and
Wernicke's encephalopathy. Dialysis
dementia, which was prevalent during the 1970s, has reduced in frequency with the use of
aluminium free
dialysate. With the introduction of
transplantation and the concomitant use of powerful immunosuppressive drugs, the pattern of neurological problems encountered in
renal replacement therapy has shifted. Five per cent of patients develop nerve
injuries during
renal transplantation, and up to 40% of patients experience neurological side effects from
cyclosporine. Furthermore,
CNS infections, often fungal in type, have been reported in up to 45% of transplant patients coming to postmortem. The nature of the involvement of neurologists with their nephrology colleagues is therefore evolving.