Hyponatremia is the most frequently observed electrolyte abnormality in clinical practice, and its frequency is almost double in hospitalized cancer patients. As a subset of cancer, hyponatremia is quite common in lung cancer patients, and it is often coupled with the diagnosis of syndrome of inappropriate antidiuretic hormone secretion. The presence of hyponatremia is consequential in that its presence adversely affects cancer patients' prognosis and outcomes. Limited data suggest that correcting hyponatremia in lung cancer patients can increase response to anticancer treatment, may help reduce length of hospital stay and cost, and reduce morbidity and mortality. The type of treatment for hyponatremia depends on several factors; the key factors are the duration and severity of neurological symptoms of hyponatremia and the status of extracellular volume. When hyponatremia is caused by syndrome of inappropriate antidiuretic hormone, hypertonic saline is indicated for acute symptomatic cases, whereas fluid restriction is recommended in chronic asymptomatic hyponatremia. The latter allows a slower rate of correction, thus avoiding the dreaded complication of osmotic demyelination syndrome. Fluid restriction is, however, insufficient or impractical, and often the use of pharmacological therapy such as antidiuretic hormone receptor antagonists becomes necessary. Availability of these antagonists as an effective treatment in the management of hyponatremia has been a major breakthrough, and furthermore, its clinical or investigational use in cancer-related hyponatremia may offer a potential opportunity to gain further insights into the prognostic impact of hyponatremia correction on cancer patients' outcomes. Tolvaptan is a prototype of ADH receptor antagonists that acts at renal tubular levels to increase free water excretion without inducing major systemic electrolyte abnormalities such as hypokalemia or alkalosis. The aim of this paper is to provide a brief review while focusing on cancer hyponatremia; (1) of the epidemiology of hyponatremia and its pathophysiology and diagnostic approaches and (2) of the pharmacokinetics of tolvaptan and its clinical efficacy, safety, and compliance.

Gemcitabine is a potent and widely used anticancer drug. We report a case of gemcitabine-induced thrombotic microangiopathy (GCI-TMA), a known but not widely recognized complication of gemcitabine use, and our experience of treating GCI-TMA with rituximab. A 74-year-old woman was referred to our clinic for an evaluation of worsening renal function. She has recently been treated for ovarian cancer (diagnosed in 2011) with surgery (tumor debulking and bilateral salpingo-oophorectomy) along with cisplatin chemotherapy in 2012, followed by carboplatin/doxorubicin in 2013 and recent therapy for resistant disease with gemcitabine. Laboratory tests showed anemia, normal platelets and elevated lactate dehydrogenase. A peripheral smear revealed numerous schistocytes, and a kidney biopsy showed acute as well as chronic TMA. The patient continued on gemcitabine therapy, and treatment with plasma exchange was started. Since there was no response to treatment even after 5 sessions of plasma exchange, one dose of rituximab was given, which was associated with a drop in the creatinine level to 2 mg/dl. The pathogenesis of renal injury could be the effect of direct injury to the endothelium mediated by cytokines. Usual treatment includes withdrawing the drug and initiation of treatment with plasmapheresis with or without steroids. In cases resistant to plasmapheresis, treatment with rituximab can be tried. The mechanism of action of rituximab might be due to the reduced production of B-cell-dependent cytokines that drive endothelial dysfunction by depleting B cells. Patients receiving gemcitabine chemotherapy should be monitored for the development of TMA, and early treatment with plasma exchange along with rituximab might benefit these patients who already have a bad prognosis.

RATIONALE & OBJECTIVE: Kidney biopsy data inform us about pathologic processes associated with infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We conducted a multicenter evaluation of kidney biopsy findings in living patients to identify various kidney disease pathology findings in patients with coronavirus disease 2019 (COVID-19) and their association with SARS-CoV-2 infection. STUDY DESIGN: Case series. SETTING & PARTICIPANTS: We identified 14 native and 3 transplant kidney biopsies performed for cause in patients with documented recent or concurrent SARS-CoV-2 infection treated at 7 large hospital systems in the United States. OBSERVATIONS: Men and women were equally represented in this case series, with a higher proportion of Black (n=8) and Hispanic (n=5) patients. All 17 patients had SARS-CoV-2 infection confirmed by reverse transcriptase-polymerase chain reaction, but only 3 presented with severe COVID-19 symptoms. Acute kidney injury (n=15) and proteinuria (n=11) were the most common indications for biopsy and these symptoms developed concurrently or within 1 week of COVID-19 symptoms in all patients. Acute tubular injury (n=14), collapsing glomerulopathy (n=7), and endothelial injury/thrombotic microangiopathy (n=6) were the most common histologic findings. 2 of the 3 transplant recipients developed active antibody-mediated rejection weeks after COVID-19. 8 patients required dialysis, but others improved with conservative management. LIMITATIONS: Small study size and short clinical follow-up. CONCLUSIONS: Cases of even symptomatically mild COVID-19 were accompanied by acute kidney injury and/or heavy proteinuria that prompted a diagnostic kidney biopsy. Although acute tubular injury was seen among most of them, uncommon pathology such as collapsing glomerulopathy and acute endothelial injury were detected, and most of these patients progressed to irreversible kidney injury and dialysis.