OR25-04 Over 14% of Inpatients with Euvolemic Hyponatremia Have Undiagnosed Adrenal Insufficiency

Background- The commonest cause of euvolemic hyponatremia (EvHNa) is the syndrome of inappropriate antidiuretic hormone secretion (SIADH). The diagnosis of SIADH requires the exclusion of secondary adrenal insufficiency (AI) and untreated hypothyroidism. Studies have suggested about 4% of unselected patients presenting to the emergency room with EvHNa have undiagnosed SAI.(1) Among patients admitted to specialized endocrine units this prevalence maybe as high as 20%.(2)Objective- To study the prevalence of undiagnosed AI among inpatients with EvHNa admitted to general medical wards. Methods- This was a prospective, single centre observational study conducted among inpatients with EvHNa. EvHNa was defined as patients with a serum sodium (Na) <135 mEq/L, with no clinical evidence of dehydration or fluid excess, and a urine spot Na >30mmol/L. In addition patients with recent vomiting, renal failure, recent diuretic use, uncontrolled hyperglycemia and patients with history of use of oral or parenteral steroids in the last 6 months were excluded. Adrenal functions were assessed by a modified porcine ACTH stimulation test which has been described recently by Nair et al. A cut off cortisol value of <18mg/dl after 60 minutes of ACTH injection was used to diagnose AI.(3)Results- One hundred and forty one (141) patients were included after informed consent and all underwent a modified ACTH stimulation test. They had a mean age of 58 years and 52.3% (n=74) were males. Modified ACTH stimulation testing suggested 20/141 (14.2%) had undiagnosed AI. The mean age among those with AI was 55.2 years. In only 25% (5/20) AI was suspected based on clinical presentation by the treating physician. Despite excluding patients with documented steroid use, the commonest cause of AI (9/20) was secondary AI due to exogenous steroid use including high potency inhaled steroids (5/9) and the use of undocumented steroids or steroid containing medicaments by alternative practitioners (4/9). Hypopituitarism was diagnosed as the cause of AI in 5 patients, which included unsuspected Sheehan’s syndrome in post menopausal women (3/5), non functioning pituitary adenoma (1/5) and lymphocytic hypophysitis (1/5). Despite primary AI not commonly presenting as EvHNa, 3/20 patients had primary AI and in the remaining 3 patients the aetiology of AI remained unclear. Conclusions- Undiagnosed AI is much more common in our country among inpatients presenting with EvHNa to medical units. This increase is primarily driven by inhaled and undocumented exogenous steroid use and undiagnosed Sheehan’s syndrome. An assessment of the hypothalamic-pituitary-adrenal axis is mandatory before making a diagnosis of SIADH. References -(1) Diederich et al. Eur J Endocrinol 2003; 148: 609-617. (2) Cuesta et al. Clin Endocrinol (Oxf) 2016; 85: 836-844. (3) Nair A et al. Eur J Endocrinol. 2019 Oct 1. pii: EJE-19-0558.R2.