Unmasking of Partial Diabetes Insipidus during Stress but Not Maintenance Dosing of Glucocorticoids in an Infant with Septo-Optic Dysplasia

Septo-optic dysplasia (SOD) is a malformation syndrome in which at least 50% of children have associated hypopituitarism [1, 2]. This condition includes agenesis of the septum pellucidum, hypoplasia, or aplasia of the optic nerves and chiasm that results in various degrees of visual impairment and abnormality of the hypothalamus causing secondary hypopituitarism [3]. Diabetes insipidus (DI) is a condition characterized by excretion of large volumes of dilute urine secondary to either a deficiency in the production/release of the hormone arginine vasopressin (AVP) that is synthesized in the hypothalamus and transported and stored in the posterior pituitary for release in response to a rise in plasma concentrations of osmotically active substances or an impaired response or resistance to AVP at the level of the kidney (nephrogenic DI, 4). The most common form of DI is due to a primary deficiency of AVP. Central DI due to midline brain abnormalities may also be accompanied by a defective thirst mechanism [4].Here we present an infant in whom DI was not present during maintenance GC replacement but was unveiled during two episodes in which "triple stress GC dosing" was accompanied by temporary DI.Patient is a 2-month-old female with SOD diagnosed in the newborn period secondary to hypoglycemia and hypotonia. SOD was confirmed by both MRI and ophthalmologic exam. Hypopituitarism manifested with central hypothyroidism and hypoadrenalism such that her medications at presentation included thyroid supplementation (37.5？mcg or 10？mcg/kg/day) and hydrocortisone (8？mg/m2/day).On day of life no. 70, she presented to the ED at the OSH with apnea and lethargy (which responded to stimulation), dehydration, and hypothermia (temperature 33.78). She underwent a septic workup, including urine and blood cultures, that were negative. Of note, her initial serum sodium (Na) was 153？mmol/L (range 135–145？mmol/L). She received a dose of ceftriaxone and an initial stress dose GC of 25？mg (100