Although SIAD appears in principle as the main determinant of hyponatremia in COVID-19 infection, other etiologies may be present. However, natremia was significantly lower in patients with pulmonary involvement ( 14).
#Serum 2 series
Analyses from series of patients in China reported a median serum of 138 mEq/L ( 13). The prevalence of hyponatremia in COVID-19 patients has not been clearly defined, so far ( 11, 12). Hyponatremia occurs in about 30% of patients with pneumonia ( 7) and it has been previously reported in 30–60% of SARS CoV-1 patients ( 8, 9, 10). More than 1 400 000 patients died because of COVID-19 infection by the end of November 2020. In its severe form, COVID-19 infection can cause interstitial pneumonia, multiple organ failure and death. It originated in Wuhan (China) and it spread throughout the world with more than 62 000 000 affected patients by the end of November 2020 (COVID-19 Dashboard by the Center for System Science and Engineering (CSSE) at John Hopkins University ( 6). The COVID-19 infection is caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS CoV-2).
Therefore, IL-6 appears to play an important role in the pathogenesis of hyponatremia secondary to SIAD. In addition, IL-6 can directly induce vasopressin secretion by binding to IL-6 receptors expressed by the cells of the SON and the PVN ( 5).
This, in turn, induces vasopressin release by the supraoptic (SON) and the paraventricular nuclei (PVN) ( 4). IL-6 can cross the blood-brain barrier and activates the circumventricular organs by binding to IL-6 receptors. In these situations, vasopressin secretion is mainly due to interleukin-6 (IL-6), which is released by monocytes and macrophages. Noteworthy, infectious diseases and inflammatory conditions are effective triggers for non-osmotic induction of vasopressin secretion. However, the prevalence may be even higher in some pathological conditions, including, for instance, pneumonia, subarachnoid hemorrhage and traumatic brain injury ( 3). The syndrome of inappropriate antidiuresis (SIAD) is the cause of hyponatremia in 40–50% of cases. Hyponatremia, defineed as a serum sodium concentration <135 mEq/L, is the most common electrolyte disorder in hospitalized patients (up to 30%) ( 1, 2). | 14 Geriatric-UTIG Unit, Careggi University Hospital, Florence, Italy.| 13 Department of Internal and Emergency Medicine, Careggi Hospital, Florence, Italy.| 12 High Intensity Internal Medicine Unit, Careggi University Hospital, Florence, Italy.| 11 Intensive Care Unit and Regional ECMO Referral Center, Careggi University Hospital, Florence, Italy.
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