Pericardial effusion in hypothyroidism—responsible for up to 14% of all pericardial effusions¹⁻²—is thought to be related to an increase in permeability of the pericardial capillaries to serum proteins (eg, albumin) resulting in an exudative effusion.³   Increased capillary permeability may in turn be due to the release of histamine by mastocytes or a direct effect of thyroid hormone deficiency on vascular endothelial integrity. ¹⁻³ In addition, hypothyroidism can be associated with pulmonary hypertension and a decrease in catecholamines, both of which can impair lymphatic drainage and further exacerbate the effusion.¹

Of note, myxedema — the accumulation of acid mucopolysaccharides causing fluid retention –– by itself does not explain the accumulation of pericardial fluid, as there is a lack of acid mucopolysaccharide buildup in the pericardial space.¹⁻² Autoimmune processes also do not appear to play a role in this context as pericardial disease can occur in both autoimmune (eg, Hashimoto thyroiditis) and non-autoimmune hypothyroidism.¹ Thus, the pericardial effusion in hypothyroidism seems to be a direct consequence of the metabolic effects of thyroid hormone deficiency itself. 

Occasionally, pericardial effusion in hypothyroidism is not so “benign” and can be complicated by tamponade.¹ In addition to timely percutaneous or surgical drainage of the effusion, thyroid hormone supplementation should be initiated without delay. ¹⁻² Although most pericardial effusions resolve over several months with adequate thyroid supplementation, they may recur in severe or chronically untreated hypothyroidism due to persistent alterations in the pericardial vascular permeability and impaired lymphatic drainage. ¹⁻³ This is another reason to remind patients to not go off their thyroid supplementation!

Bonus pearl: Did you know that the attendant increase in metabolic demands, plasma volume and higher levels of thyroxine-binding globulin in pregnancy necessitates routine upward titration of levothyroxine in pregnant patients with hypothyroidism? ⁵

Contributed by: Sarah de la Serna, Ponce Health Sciences University, St. Louis, MO and Tony Hiran, MD, Mercy Hospital, St. Louis, MO

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References

1. Chahine J, Ala CK, Gentry JL, Pantalone KM, Klein AL. Pericardial diseases in patients with hypothyroidism. Heart. 2019 Jul;105(13):1027-1033. doi: 10.1136/heartjnl-2018-314528. Epub 2019 Apr 4. PMID: 30948517. Pericardial diseases in patients with hypothyroidism – PubMed
2. Chaker L, Papaleontiou M. Hypothyroidism: A Review. JAMA. Published online September 03, 2025. doi:10.1001/jama.2025.13559. Hypothyroidism: A Review | Endocrinology | JAMA | JAMA Network
3. González Vílchez F, Castillo L, Pi J, Ruiz E. Manifestaciones cardíacas del hipotiroidismo primario. Factores determinantes y respuesta al tratamiento [Cardiac manifestations of primary hypothyroidism. Determinant factors and treatment response]. Rev Esp Cardiol. 1998 Nov;51(11):893-900. Spanish. PMID: 9859712. [Cardiac manifestations of primary hypothyroidism. Determinant factors and treatment response] – PubMed
4. Kerber RE, Sherman B. Echocardiographic evaluation of pericardial effusion in myxedema. Incidence and biochemical and clinical correlations. Circulation. 1975 Nov;52(5):823-7. doi: 10.1161/01.cir.52.5.823. PMID: 126121. Echocardiographic evaluation of pericardial effusion in myxedema. Incidence and biochemical and clinical correlations – PubMed
5. Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid : Official Journal of the American Thyroid Association. 2017;27(3):315-389. doi:10.1089/thy.2016.0457. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum – PubMed

Disclosures/Disclaimers: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!