Supplemental Material for: Persistent Elevation of Thyroid-Stimulating Hormone Despite Levothyroxine Therapy Revealing Autoimmune Adrenal Insufficiency in an Adolescent With Autoimmune Thyroiditis: A Case Report and Review of Literature

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Introduction: Autoimmune thyroiditis (AIT) or Hashimoto thyroiditis is the most common cause of acquired hypothyroidism in the developed nations and these patients are at increased risk for other autoimmune conditions including autoimmune adrenal insufficiency (AAI). Routine screening for AAI is not recommended in asymptomatic children with AIT. The coexistence of AAI and AIT establishes the diagnosis of autoimmune polyglandular syndrome type 2 (APS-2), a rare disorder that is predominantly diagnosed in adults, with limited data available in pediatric patients.We report an adolescent male with AIT who was subsequently diagnosed with AAI during evaluation for persistently elevated thyroid-stimulating hormone (TSH) levels despite reported adherence to levothyroxine therapy. We performed literature review on pediatric patients with AIT and AAI and identified 20 patients from 19 published case reports. Case presentation: An adolescent male was diagnosed with AIT at 12 years 10 months of age. Six months later, he developed hypothyroidism and was started on levothyroxine. Despite reported adherence, TSH levels remained above target, necessitating progressive dose escalation to 125 µg daily (2.2 µg/kg/day) over the subsequent 16 months. At that time, he reported intermittent headaches, dizziness, and fatigue. Growth parameters and vital signs remained normal, although retrospective review revealed hyperpigmentation over the preceding two years. Laboratory evaluation demonstrated: sodium 128 mEq/L (136-143 mEq/L), potassium 6.7 mEq/L (3.8-4.9 mEq/L), cortisol 0.3 mcg/dL (3.6-17.0 mcg/dL), aldosterone < 1 ng/dL(ref. 4-48 ng/dL), renin 10.0 ng/mL/h (0.25-5.82 ng/mL/h), adrenocorticotropic hormone 1184 pg/mL (9-57 pg/mL), and positive 21-hydroxylase antibodies, confirming the diagnosis of AAI. He was treated with intravenous fluids, stress-dose hydrocortisone, and fludrocortisone, followed by maintenance glucocorticoid and mineralocorticoid replacement. Thyroid function subsequently normalized with continued levothyroxine therapy. Conclusions: Our case highlights the importance of considering AAI in children with autoimmune thyroiditis who have persistent elevation of TSH despite levothyroxine therapy, particularly when accompanied by suggestive clinical features or biochemical abnormalities. Although persistently elevated TSH is nonspecific and may have multiple explanations, including variable adherence or absorption, recognition of coexisting AAI is essential to avoid delayed diagnosis and potentially life-threatening adrenal crisis.

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