Hyperuricaemic (gouty) nephropathy
Disorders of uric acid metabolism may cause renal disease due to a chronic nephropathy, an acute nephropathy or through the formation of uric acid stones.
There is still a debate as to whether patients who have hyperuricaemia, gouty tophi, and chronic renal failure have gouty nephropathy as the cause for their renal impairment. Renal failure leads to raised uric acid levels and in some cases there may have been another cause for their renal failure. It is thought that urate crystals deposit in the renal interstitium, causing chronic inflammation, interstitial fibrosis and hence the development of chronic renal failure.
There is a distinct autosomal dominant disorder of uric acid metabolism which is associated with early onset renal failure and hypertension. This is called familial juvenile gouty nephropathy, although it is still unclear whether uric acid deposition is the primary cause. Allopurinol may improve renal function, but rarely completely prevents deterioration.
This occurs when there is an acute rise in uric acid as in patients who have haematological malignancies or polycythaemia rubra vera. Prior to treatments such as chemotherapy or radiation which cause acute cell lysis, prophylactic treatment may be required. Acute hyper-uricaemia may also occur in conjunction with tumour lysis syndrome (i.e. with hyperkalaemia, hyperphos-phataemia and hypocalcaemia). Uric acid crystals precipitate in the collecting ducts, renal pelvis and ureters, causing obstruction.
Patients present with acute oligoanuric renal failure, sometimes with loin pain or colic. There are very high uric acid levels and uric acid crystals may be seen on urine microscopy unless there is little or no urine production.
This complication is prevented by pretreatment with high doses of allopurinol or rasburicase prior to chemotherapy or radiation, and giving intravenous fluids to lower the concentration of uric acid in the urine. Despite this, some patients still develop ARF in which case fluid and diuretics are given to try to flush out the crystals. Haemodialysis may be used to remove circulating uric acid.