Hashimoto thyroiditis with an unusual presentation of cardiac tamponade in Noonan syndrome.

Noonan syndrome is an autosomal dominant, multisystem disorder. Autoimmune thyroiditis with hypothyroidism is an infrequent feature in patients with Noonan syndrome. A 16-year-old boy was admitted because of chest discomfort and dyspnea; an echocardiogram revealed pericardial effusion. Additional investigations led to a diagnosis of severe hypothyroidism due to Hashimoto thyroiditis. The patient was treated with L-thyroxine at 0.15 mg daily. However, during admission, he developed symptoms of cardiac tamponade. Closed pericardiostomy was performed, after which the patient's chest discomfort improved, and his vital signs stabilized. Herein, we report a case of an adolescent with Noonan syndrome, who was diagnosed with Hashimoto thyroiditis with an unusual presentation of cardiac tamponade.