Diabetes insipidus (DI) occurs in 1/30,000 pregnancies and can be difficult to recognize due to normal peripartum physiology. The most common etiology is excess production of placental vasopressinase, which degrades maternal anti-diuretic hormone. Although rare, hypothalamic and pituitary disorders must also be considered in pregnant patients presenting with DI. We present the case of a pregnant woman presenting with diabetes insipidus and pituitary apoplexy.
We were called to see a 33 year old female with polyuria and polydipsia on post-partum day #2. She had presented to the ED at 29.4 weeks of her 5th pregnancy (G5P4) with an unrelenting headache, nausea, and vomiting for 12 hours. She was tachycardic, hypertensive, and had no focal neurologic deficits. Fetal evaluation was reassuring. Admission labs included serum sodium of 147 mEq/L (n 136-145), serum potassium 2.8 mEq/L (n 3.4-4.4), and urine specific gravity of 1.003 (n 1.005-1.030). Glycemic parameters, renal function, and hepatic function were normal. She remained tachycardic despite vigorous IV fluid administration. Overnight into hospital day #3 she began to have uterine contractions with fetal decelerations, and betamethasone was given. It was noted that she had produced 8L of urine over the preceding 24 hours. Serum sodium was 159 mEq/L with urine osmolality of 78 mOsmol/kg (n 300-900). A presumptive diagnosis of gestational DI was made and 2 mcg of subcutaneous DDAVP was given. Shortly thereafter she delivered a healthy infant. Maternal blood loss was minimal. Over the next 12 hours her urine became concentrated and her serum sodium decreased, but by the next morning she re-developed dilute polyuria.
At the time of our evaluation, her headache had resolved and she had no focal neurologic deficits. She had no apparent signs of glucocorticoid or thyroxine deficiency but had not begun to lactate. Biochemical evaluation included early morning cortisol of 4.6 ug/dL (n 3.5-18.3), TSH 0.46 uIU/mL (n 0.35-4.94), free T4 0.76 ng/dL (n 0.70-1.48), and prolactin 26.6 ng/mL (n 5.2-26.5). Pituitary MRI showed a mildly enlarged gland with central T1 hyperintensity, consistent with apoplexy. A regimen of hydrocortisone and DDAVP was initiated.
Pituitary apoplexy is uncommon during pregnancy but is potentially life-threatening for the mother and fetus if it goes unrecognized. The significant physiologic growth of the pituitary during pregnancy may increase the risk of apoplexy. A severe headache is the most common symptom and may be accompanied by signs of pituitary dysfunction. Although diabetes insipidus is more often caused by placental physiology, pituitary apoplexy must also be considered in a pregnant woman who has concurrent neurologic symptoms.