Update on the diagnosis and management of SIADH and Diabetes insipidus

Dysnatremia is a common occurrence in patients with COVID-19 and is associated with higher mortality and risk for septic conditions. The pathomechanisms are probably multifaceted, but severe hyponatremia may also occur as a result of underlying SIADH or hypocortisolism. Patients with preexisting AVP dysfunction, like SIADH or diabetes insipidus, are at high risk for severe electrolyte imbalances in the event of a COVID-19 infection. The recently growing use of immune checkpoint inhibitors in oncology is associated with a spectrum of endocrine immune-related adverse events (endocrine irAEs). These AEs usually occur unpredictably and may even manifest after discontinuation of the anticancer therapy. Hyponatremia is a common factor of several endocrine irAEs and may serve as a red flag biomarker for possibly underlying endocrine irAEs such as hypophysitis or adrenalitis. New-onset hyponatremia should always prompt a comprehensive diagnostic workup and exclusion of endocrine irAEs before the diagnosis of SIADH is made. Hyponatremia with severe symptoms should be treated with hypertonic (3 %) saline solution to resolve the cerebral edema and prevent from detrimental neurological sequelae. Both rapid intermittent bolus (RIB) therapy and continuous infusion therapy have now been reported to be safe and equally effective. The RIB therapy limits the risk of overcorrection and requires less often re-lowering treatment than continuous infusion therapy. Fluid restriction has long been considered as first-line treatment of chronic hyponatremia due to SIADH. Additional treatment with Furosemid and/or oral NaCl tablets does not improve efficacy but reduces tolerance to therapy. Copeptin-based dynamic tests show higher diagnostic accuracy in the differential diagnosis of patients with hypotonic polyuria polydipsia syndrome than the indirect water deprivation test.