MON-441 - When the TSH Rises: Hypothyroidism as a Clue to Inadequate Diuretic Response

An 89-year-old female with a past medical history of hypothyroidism, heart failure with improved ejection fraction (HFimpEF), sick sinus syndrome, chronic kidney disease stage IV, and gout presented with progressive lower extremity swelling. She reported approximately six weeks of worsening edema despite aggressive outpatient oral diuretic therapy.

She was initially treated with bumetanide, followed by a trial of torsemide, and subsequently transitioned to a combination of oral furosemide and metolazone due to persistent volume overload and inadequate diuretic response.

During hospitalization, she was transitioned to intravenous furosemide with gradual improvement in volume status. However, episodes of hypotension prompted further evaluation, including thyroid function testing. The patient had a long standing history of hypothyroidism requiring thyroid replacement hormone.

Laboratory studies revealed severe hypothyroidism with a TSH of 72.30 µIU/mL, T3 of 1.24 pg/mL, and free T4 of 0.76 ng/dL. Given her reported medication adherence, her profound hypothyroidism was attributed to impaired gastrointestinal absorption of levothyroxine in the setting of significant fluid overload and gut edema.

This case highlights that persistent hypothyroidism in patients with decompensated heart failure may serve as an indirect marker of long-standing, refractory volume overload. TSH evaluation could potentially be a useful adjunct in assessing the duration and severity of diuretic resistance, particularly when compliance with thyroid replacement therapy is not in question.

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