Large pericardial effusion as the first manifestation of severe Hashimoto’s thyroiditis: Clinical and echocardiographic insights

Introduction: Severe hypothyroidism may lead to pericardial effusion, but the development of a large effusion is uncommon. This complication results from increased pericardial capillary permeability and reduced lymphatic clearance, though most cases remain mild and clinically silent. Case presentation:We report the case of a 65-year-old patient who developed progressively worsening dyspnea, evolving from NYHA class II to class III prior to admission. Echocardiography revealed a large circumferential pericardial effusion exceeding 30 mm, notably without hemodynamic compromise. Laboratory investigations demonstrated profound hypothyroidism, with a TSH level >100,000 µU/mL and markedly reduced free T4 levels. Thyroid hormone replacement therapy led to rapid clinical improvement and complete resolution of the effusion on follow-up. Hashimoto’s thyroiditis was subsequently identified as the underlying etiology. Conclusions: This case illustrates that even markedly large pericardial effusions in severe hypothyroidism may remain hemodynamically silent and resolve fully with adequate hormonal therapy. Early recognition of hypothyroidism as a reversible cause of massive pericardial effusion is key to preventing unnecessary invasive procedures.