Severe Symptomatic SIADH as a Sign of Unknow Hypopituitarism: A Case Report

Abstract

\n Background: SIADH due to secondary adrenal insufficiency is a rare condition that can be life-threatening. Treatment with glucocorticoids is highly effective, but, as symptomatology of hypopituitarism can be mild and unspecific, a high level of clinical suspicion is necessary.\n Clinical Case: A 64-year-old postmenopausal woman, with a previously diagnosed and treated hypothyroidism and depressive syndrome, presented at the emergency room with nausea, vomits, asthenia and recurrent syncopes over the past three weeks and weight loss in the last months. One week before, she had been admitted at other hospital due to the same complaints and a serum Na+ of 112mmol/L (N 135-145 mmol/L) was detected. One year earlier, she had reported the same symptomology and hyponatremia had also been found, but no etiologic study was performed. At admission, she was conscient, hydrated, pale, hemodynamically stable, with unremarkable cardiopulmonary auscultation. A severe hyponatremia was found (Na+ 111mmol/L), with low serum osmolarity (241mOsm/Kg, N 280-301mOsm/Kg), low urine osmolality (125mOsm/kg N 300-900 mOsm/Kg) and low urinary sodium (33mmol/24h, N 40-220mmol/24h). Treatment with saline fluids was initiated and the patient was admitted for etiological investigation, which showed a low morning serum cortisol (3.7 µg/dl)) with inappropriately low-normal ACTH level (12.2 pg/mL), low FSH (15.07 mUI/mL, N 23.0-116.3 mUI/mL) and LH (4.28 mUI/mL, N 15.9-54 mUI/mL), estradiol of 78.81 pmol/L (N <118.2 pmol/L), undetectable IGF-1 (<25 ng/mL, N 36-244 ng/mL) and PRL of 21.98 ng/mL (N 1.8-20.3 ng/mL). Under 50µg of levothyroxine, TSH was 2.5 µUI/mL (N 0.358-3.74 µUI/ml), and FT4 was 1.1 ng/dL (N 0.76-1.46 ng/dL). Anti-thyroglobulin and anti-TPO antibodies were negative. A pituitary MRI revealed an empty sella with arachnoidocele. Other differential diagnosis of SIADH were excluded. The patient was started on oral hydrocortisone 30 mg/day, with a remarkable recovery, with better mood, more energy and appetite, resolution of all symptoms and normalization of the natremia.\n Conclusion: Hypopituitarism due to an empty sella is a relative rare disorder, whose etiology may be difficult to prove. It usually develops insidiously, with unspecific symptoms, which often delays the diagnosis. In our patient, this severe hyponatremia likely developed over a long time, allowing adaptation to such low levels of Na+. Moreover, the presence of a previously diagnosed hypothyroidism raises the suspicion if this wasn’t the first manifestation of the pituitary disease and if treatment of levothyroxine did not worsen an undetected secondary adrenal insufficiency.