Abstract #1400722: False Sense of Security: ACTH Stimulation Testing in Secondary Adrenal Insufficiency

In euvolemic hyponatremia, endocrinopathies such as hypothyroidism and adrenal insufficiency are possible etiologies. Secondary (SAI) can cause hyponatremia due to impaired free water excretion. Panhypopituitarism is a etiology of gradual onset where gonadotropins (FSH, LH) lose production followed by TSH ACTH. We present case an ACTH stimulation test misled the diagnostic workup. A 69-year-old woman was admitted our hospital with dizziness, weakness, nausea vomiting. MRI revealed 1.8 cm pituitary cyst. She had history meningioma surgery several years prior. Sodium 121 mEq/L, serum osmolarity 250 mOsm/Kg, potassium 4.3 uric acid 2.3 mg/dL, urine 466 sodium 80 3.01 uIU/mL, Free T4 0.62 ng/dL cortisol 3.2 ug/dL. performed baseline 2.2 ug/dL, 30 minutes 13 60 20.3 Patient treated SIADH but did not improve clinically or chemically. soon reported undetectable negligible (FSH 1.6 mIU/ml LH 0.2 mIU/ml). Two prior FSH 38.7 mIU/ml, 13.0 mIU/ml. One year prior, 6 1.9 17.3 pg/ml. Subsequently, patient steroids rapidly improved Diagnosing SAI be challenging. insidious in difficult recognize despite close laboratory monitoring. patient, there sharp falloff one-year which should have prompted further evaluation for SAI. Cortisol secretion pulsatile sometimes hard interpret this setting. Insulin tolerance testing gold standard rarely performed. 1 microgram has sensitivity 83% high dose only 64%. An abnormal specificity case, delayed diagnosis hypopituitarism, particularly SAI, could disastrous consequences. False reassurance from guarded against.