Massive Pericardial Effusion as a Manifestation of Severe Autoimmune Hypothyroidism in an Adolescent With Down Syndrome: Importance of Early Recognition and Thyroid Hormone Replacement

The clinical features of severe hypothyroidism may overlap with those of Down syndrome, delaying diagnosis until complications such as myxedema crisis and massive pericardial effusion develop. Regular thyroid function screening is essential, and hypothyroidism-associated massive pericardial effusion can often be treated conservatively with levothyroxine in the absence of cardiac tamponade.