Renal underexcretion of uric acid is present in patients with apparent high urinary uric acid output.

OBJECTIVE: To compare renal handling of uric acid in patients with primary gout with that of a control group. METHODS: A case-control study of 100 patients with primary gout and 72 healthy controls was undertaken. Creatinine clearance, uric acid clearance, 24-hour uric acid urinary excretion, fractional excretion of uric acid, excretion of uric acid per volume of glomerular filtration, urinary uric acid to creatinine ratio, and glomerular uric acid filtered load were calculated using 24-hour urine samples. After treatment with allopurinol to achieve similar glomerular filtered load of uric acid, patients were again compared with controls. RESULTS: Patients with gout showed lower uric acid clearance, fractional excretion of uric acid, excretion of uric acid per volume of glomerular filtration, and urinary uric acid to creatinine ratio than controls at baseline, when patients showed hyperuricemia. Although the glomerular uric acid filtered load was much higher in patients with gout than controls, 24-hour uric acid excretion was not statistically different. After treatment with allopurinol, and achieving similar uric acid filtered loads, patients still showed lower figures than controls. When patients with 24-hour urinary uric acids levels >700 mg/day were compared with controls, they had lower uric acid clearance and fractional excretion of uric acid than controls, both at baseline and after achieving similar filtered loads with allopurinol therapy. CONCLUSIONS: Renal underexcretion is the main mechanism for the development of primary hyperuricemia in gout, but even patients showing apparent high 24-hour uric acid output show lower uric acid clearance than controls, indicating that relative, low-grade underexcretion of uric acid is at work.

"Pseudoseptic" pseudogout associated with hypomagnesemia in liver transplant patients.

Hypomagnesemia has been associated with deposition of calcium pyrophosphate dihydrate crystals in articular structures, causing pseudogout, also known as calcic gout. Occasionally, pseudogout may mimic septic arthritis; this "pseudoseptic" attack may be of especial concern in the immunocompromised host, such as transplant recipient patients, who may be indeed at risk of developing septic arthritis. We report the cases of two patients in whom pseudogout developed after liver transplantation. Synovial fluid appearance and leukocyte counting in synovial fluid mimicked septic arthritis, but calcium pyrophosphate dihydrate crystals were observed. Magnesium depletion before transplantation and further tacrolimus-induced renal magnesium leakage were probably working in these patients.

Improvement of renal function in patients with chronic gout after proper control of hyperuricemia and gouty bouts.

AIM: To evaluate the effect of nonsteroidal anti-inflammatory drug (NSAID) withdrawal on renal function in patients with chronic gout after proper control of hyperuricemia and gouty symptoms. METHODS: Patients with chronic gout, who regularly used NSAIDs to control gouty symptoms prior to urate-lowering therapy, were prospectively followed up in an observational study. Risk factors for renal function impairment were recorded, and the clearance of creatinine (Ccr) was initially measured while on colchinine therapy to prevent gouty bouts. Therapy with urate-lowering drugs was started in order to keep serum urate levels under 6.0 mg/dl (275 micromol/l), and the Ccr was monitored during the follow-up period. Final assessment of the renal function was made after 1 year free from gouty bouts and without NSAID therapy during this period. RESULTS: 87 patients completed a 1-year period of NSAID withdrawal. Low initial Ccr was related to age, hypertension, hypertriglyceridemia and the presence of previous renal diseases. After proper control of gout and NSAID withdrawal during 1 year, the mean Ccr significantly raised from 94 to 104 ml/min. The improvement was especially significant in patients whose initial Ccr was under 80 ml/min. Their mean Ccr rose from 60 to 78 ml/min, and 12 of 29 patients achieved normal Ccr at the end of the study. No risk factor correlated with improvement of the renal function. CONCLUSIONS: Renal function impairment in patients with chronic gout is mainly related to vascular risk factors, but improvement of the renal function was observed after proper control of hyperuricemia and NSAID withdrawal. Optimal control of hyperuricemia and, therefore, of symptoms of gout should be especially considered in patients with vascular risk factors in order to avoid renal function loss due to NSAID use.