**2. Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)**

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is characterized by impaired water excretion secondary to the inability to inhibit antidiuretic hormone (ADH) secretion for multiple reasons, which lead eventually to different clinical presentations including hyponatremia [13, 14].

*Coronavirus 19 (COVID-19) and Syndrome of Inappropriate Anti-Diuretic Hormone Secretion… DOI: http://dx.doi.org/10.5772/intechopen.110717*

SIADH-induced hyponatremia in COVID-19 patients is not fully understood. One of the speculated hypotheses is related to burst release of inflammatory cytokines, including interleukin IL-1 and IL-6. IL-6 triggers hypothalamic arginine vasopressin production with consequent hyponatremia [15, 16].

SIADH should be considered in the differential diagnosis of any patient presented with hyponatremia (serum sodium levels <135 mmol/L) particularly when it associated with plasma hypo-osmolality, diluted urine and high urinary sodium (>40 mEq/L). Notably and unlike other causes of euvolemic hyponatremia like adrenal insufficiency, in SIADH, the serum potassium level is normal, no acid-base disturbance is observed and the serum uric acid level is frequently low [17].
