Recurrent exercise-induced acute renal failure in renal hypouricemia

Hypouricemia: what the practicing rheumatologist should know about this condition

We presented an update in the field of hypouricemia, which is defined as a serum urate concentration of < 2 mg/dL (119 μmol/L), for the practicing rheumatologist, who usually is the consulting physician in cases of disorders of urate metabolism. We performed a narrative review through a literature search for original and review articles in the field of human hypouricemia published between January 1950 and July 2018. We divided the etiology of hypouricemia into two main categories: those associated with a decrease in urate production and those promoting the elimination of urate via the kidneys. The most common conditions associated with these categories are discussed. Furthermore, the etiology of hypouricemia may be associated with certain medications prescribed by the practicing rheumatologists, such as the following: urate-lowering drugs (allopurinol and febuxostat); recombinant uricase (pegloticase); uricosuric agents (probenecid, benzbromarone); urate transporter URAT1 inhibitor (lesinurad); angiotensin II receptor blocker (losartan); fenofibrate; high-dose trimethoprim-sulfamethoxazole; some NSAID; and high-dose salicylate therapy. The rheumatologist is considered an expert in the metabolism of urate and its associated pathological conditions. Therefore, specialists must recognize hypouricemia as a biomarker of various pathological and potentially harmful conditions, highlighting the importance of conducting a deeper clinical investigation to reach a more accurate diagnosis and treatment.

Lesinurad: what the nephrologist should know

Lesinurad is an oral inhibitor of the monocarboxylic/urate transporter URAT1 encoded by the SLC22A12 gene. Market authorization was granted in February 2016 in Europe and December 2015 in the USA. As a potentially nephrotoxic uricosuric drug acting on the kidney, nephrologists should become familiar with its indications and safety profile. The approved indication is treatment of gout in combination with a xanthine oxidase (XO) inhibitor in adult patients who have not achieved target serum uric acid levels with an XO inhibitor alone. It is not indicated for asymptomatic hyperuricaemia or for patients with estimated creatinine clearance <45 mL/min. The only authorized daily dose is 200 mg and cannot be exceeded because of the nephrotoxicity risk. Nephrotoxicity is thought to be related to uricosuria. At the 200 mg/day dose, serum creatinine more than doubled in 1.8% of lesinurad patients (versus 0% in placebo) and in 11% of these it was not reversible. In addition, it is subject to a risk management plan given the potential association with cardiovascular events. In randomized clinical trials, the association of lesinurad with either allopurinol or febuxostat achieved a greater reduction in serum uric acid (∼1 mg/dL lower) than the XO inhibitors alone, and this allowed the serum uric acid target to be met in a higher proportion of patients, which was the primary endpoint. However, no clinical differences were observed in gout flares or tophi, although these were not the primary endpoints.

Evaluation of exercise-induced acute renal failure in renal hypouricemia using Tc-99m DTPA renography

We present a case of a thirty-eight-year-old man who had exercise-induced acute renal failure (exercise-induced ARF). He experienced oliguria, general fatigue, and vague discomfort in the lower abdomen after he exercised. As he had suffered from hypouricemia before, he was diagnosed as having exercise-induced ARF associated with hypouricemia. Enhanced computed tomography (CT) images showed patchy wedge-shaped contrast enhancement on his bilateral kidneys, consistent with characteristic observations for exercise-induced ARF. Tc-99m diethylene triamine pentaacetic acid (DPTA) renography revealed decreases in both the renal blood flow (RBF) and glomerular filtration rate (GFR), and revealed parenchymal dysfunction of the bilateral kidneys. Renogram revealed a hypofunctional pattern on the bilateral kidneys. CT images and Tc-99m DTPA renography also had improved when the symptoms of exercised-induced ARF indicated improvement. It has been hypothesized that one cause of exercise-induced ARF may be renal vasocontraction. Although CT images are useful in evaluating exercise-induced ARF, Tc-99m DTPA renography can more easily and safely evaluate renal function. We also show that Tc-99m DTPA renography is useful in precisely evaluating the degree of improvement of exercise-induced ARF.

Exercise-induced acute renal failure associated with renal hypouricaemia: results of a questionnaire-based survey in Japan

BACKGROUND

A retrospective investigation was conducted to define the clinical features of exercise-induced acute renal failure (ARF) associated with renal hypouricaemia with the aim of clarifying further the clinical features of the disease entity.

METHODS

A questionnaire was mailed to 43 institutions in Japan that had experienced case(s) of exercise-induced ARF associated with renal hypouricaemia. Fifty-four patients (48 males and six females) were identified from 38 institutions.

RESULTS

Median age at the first episode of ARF was 17 years (range 11-46). The maximal serum uric acid and creatinine levels were 4.40+/-2.49 (range 0.4-13.3) and 5.45+/-3.33 mg/dl (range 1.10-17.7), respectively. The serum uric acid level after recovery was 0.70+/-0.25 mg/dl (range 0.1-1.4). The short-term prognosis seemed to be good and histological findings in 28 patients showed minimal change or acute tubular necrosis except for one patient with chronic lesions. ARF episodes occurred predominantly in September, October and May, mostly after strenuous exercise such as a short-distance race. The first symptoms were nausea/vomiting in 51 episodes, loin pain in 35, abdominal pain in 22, general fatigue in 16 and low-grade fever in seven. Thirteen patients (24.1%) experienced recurrent ARF at various intervals. Univariate and multivariate analyses failed to demonstrate any risk factor of ARF recurrence, although no female patients experienced ARF recurrence.

CONCLUSIONS

The reason for the heterogeneity in ARF associated with renal hypouricaemia remains unknown. Further studies, especially on molecular mechanisms, are required to establish the best guidance against ARF recurrence.

Two male siblings with hereditary renal hypouricemia and exercise-induced ARF

Familial renal hypouricemia with exercise-induced acute renal failure (ARF) is rare. A 45-year-old man presented with abdominal pain, vomiting, and oliguria after severe exercise. The diagnosis was ARF based on high serum creatinine (SCr) level (5.1 mg/dL [451 micromol/L]). Renal function recovered completely within 2 weeks of conservative treatment (creatinine clearance [Ccr], 100.4 mL/min [1.67 mL/s]). After remission, laboratory results showed serum urate (SUA) of 0.8 mg/dL (48 micromol/L), and fractional excretion of uric acid (FE(UA)) of 46%. The final diagnosis was ARF associated with idiopathic renal hypouricemia. Other diseases that could increase the excretion of urate were excluded. Because only mild responses were observed both in pyradinamide and benzbromarone loading tests, he was considered to be a presecretory reabsorption disorder type. The younger brother (42 years old) also had episodes of low and middle back pain after severe exercise and experienced similar attacks at least 5 times since the age of 29. SCr level was elevated in every attack. Hypouricemia (SUA, 1.0 mg/dL [59 micromol/L]) and high urinary urate excretion (FE(UA), 65.7%) also were detected. Renal function recovered almost completely without any specific treatment. Radiologic examination of the 2 cases showed bilateral urolithiasis probably caused by the high urinary urate excretion. Sequence analysis of a urate anion exchanger known to regulate blood urate level (URAT1 gene) in both brothers showed homozygous mutation in exon 4 (W258Stop), resulting in a premature truncated URAT1 protein. Both their parents and their children showed heterozygous mutation of the URAT1 gene. This is the first report of the 2 male siblings of familial renal hypouricemia complicated with exercise-induced ARF, with definite demonstration of genetic abnormality in the responsible gene (URAT1).

Exercise-induced acute renal failure in a girl with renal hypouricemia

A 10-year-old Japanese girl developed acute renal failure following a 100-meter dash during physical training at school. After the run, she experienced intense pain in the loins with nausea and vomiting lasting more than 12 h. On the following morning, she was found to have mild proteinuria and acute renal failure (ARF). Serum creatinine and blood urea nitrogen were elevated, but the serum uric acid level was normal (3.1 mg/dL). With recovery of renal function over the ensuing days, hypouricemia (0.6 mg/dL) became evident in the patient. Although the pathophysiological association between renal hypouricemia and ARF is not known, oxygen free radicals have been implicated in the pathogenesis for ischemic-reperfusion ARF. Superoxide production by neutrophils stimulated by N-formyl methionine leucyl-phenylalanine was normal in the patient both before and following exercise. Pyrazinamide and probenecid tests were undertaken on both the patient and her parents, who had borderline hypouricemia, to determine their renal tubular handling of uric acid. Results showed that the patient and her mother had a subtotal reabsorption defect, while the father had defective postsecretory uric acid reabsorption.