AVP and hypothyroidism: Commonly reported causes of delayed hyponatremia following an operation include syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and syndrome of inappropriate anti-diuresis (SID), an SIADH like-phenotype with suppressed arginine vasopressin (AVP) (constitutive activation of V2 receptor), cerebral salt-wasting syndrome, exogenous desmopressin administration, hypocortisolemia, and hypothyroidism [10, 14–20].