Pitfalls in the management of undiagnosed secondary adrenal insufficiency: a case report and review of the literature

BACKGROUND: Prolonged cortisol deficiency in undiagnosed central adrenal insufficiency can lead to severe hypotonic hyponatremia due to inappropriate vasopressin secretion and malnutrition caused by inhibition of orexigenic signals. Notably, although hydrocortisone-induced recovery can trigger osmotic demyelination and refeeding syndromes, no previous report has simultaneously described these complications and documented significant decreases in vasopressin levels, along with changes in urine osmolality and volume before and after hydrocortisone administration. CASE PRESENTATION: A 48-year-old Japanese man presented with fever, severe nausea, and oliguria and was brought to our hospital by ambulance due to impaired consciousness. Physical examination and laboratory analysis showed severe euvolemic hypotonic hyponatremia and low-normal glucose value. Low adrenocorticotrophic hormone and cortisol levels, undetectable 24-hour urinary free cortisol, and minimal response to corticotropin-releasing hormone indicated secondary adrenal insufficiency. Magnetic resonance imaging revealed slight pituitary swelling, suggesting hypophysitis. Treatment started with a 200 mg hydrocortisone infusion over 24 hours, and 6 hours later, the patient experienced a marked decrease in vasopressin levels, accompanied by significant dilute urine excretion and an excessively rapid increase in blood sodium levels, which posed a risk of osmotic demyelination. Rehydration with 5% dextrose and desmopressin was used to prevent this risk. Carefully adjusting plasma osmolality successfully prevented osmotic demyelination syndrome. Hydrocortisone replacement significantly increased the patient's appetite, leading to refeeding hypophosphatemia and disorientation; however, these resolved with intravenous sodium phosphate replacement. The patient developed a fever on day 12 and was confirmed to have coronavirus disease 2019. The fever subsided by day 16 with molnupiravir treatment and hydrocortisone dose adjustment, and he was discharged on day 23 with a maintenance dose of hydrocortisone. CONCLUSION: Careful management is required while administering hydrocortisone in patients with undiagnosed adrenal insufficiency, as it may cause osmotic demyelination syndrome or refeeding syndrome due to sudden changes in blood electrolytes.