Severe hyponatremia as the first sign of late-onset Schmidt’s syndrome: A case report

BACKGROUND: Schmidt’s syndrome (SS) is a rare endocrine disorder (14-20:1000000), which consists of autoimmune thyroiditis (AIT) and autoimmune Addison’s disease (aAD), and usually occurs in young adults. Here, we report a unique case of late-onset SS manifesting initially with isolated severe hyponatremia and present the hazardous outcomes of preliminary misdiagnosis. CASE PRESENTATION: A 78-year-old female presented to the emergency department with a two-day history of diarrhea, emesis and disturbances in consciousness. She also reported general fatigue and increasing weakness in the last month. Urgent laboratory findings revealed isolated severe hyponatremia (serum sodium=108 mmol/l) and initial treatment with active sodium infusions was started, although with no improvement in the patient's neurological status after 5 days (serum sodium=127 mmol/l). Meanwhile, the patient developed recurring episodes of hypoglycemia and symptoms portending adrenal crisis (blood pressure=105/58 mmHg, heart rate=96 bpm, severe whole-body muscle pain, two loose stools), which required immediate i.e. hydrocortisone treatment. Reduced blood cortisol, elevated adrenocorticotropic hormone (ACTH) and atrophic morphology of the adrenal glands in computed tomography imaging contributed to the final diagnosis of aAD and SS consequently, since the patient had a past medical history of AIT. CONCLUSION: Isolated severe hyponatremia should not be underestimated as the first sign of aAD. Appropriate cause-specific treatment is crucial in managing hyponatremia.