From Syncope to Pregnancy: A Case Report of Gestational Transient Thyrotoxicosis

With a multifactorial etiology, syncope is a fairly common clinical presentation in emergency care. During pregnancy, it can result from hemodynamic and hormonal changes. One such rare cause is hyperthyroidism. Although physiological maternal adaptation to fetal requirements can often induce mild, transient, and self-limited thyroid stimulation during the late first trimester, clinically significant thyrotoxicosis can still occur throughout pregnancy. In these cases, the most prevalent causes are gestational transient thyrotoxicosis (GTT) and Graves' disease. We report the case of a 24-year-old woman presenting to the emergency department with recurrent transient syncope, gastrointestinal symptoms, tachycardia, eyelid retraction, and tremor in the upper limbs. Laboratory analysis revealed electrolyte imbalances (metabolic alkalosis, hypokalemia, and hyponatremia), hepatic and kidney dysfunction, and a suppressed thyroid-stimulating hormone with a free thyroxine level of >7.77 ng/dL (reference range: 0.94-1.52 ng/dL), consistent with overt hyperthyroidism. After ruling out the most likely etiologies for syncope and thyroid dysfunction, including autoimmune causes, an abdominal ultrasound revealed the patient was 12 weeks pregnant. Extremely elevated serum human chorionic gonadotropin levels reinforced the presumed diagnosis of a GTT associated with hyperemesis gravidarum (HP). The patient started on fluid support with electrolyte replacement. Due to the uncommon clinical presentation, an antithyroid drug and a beta-blocker were also initiated. The patient showed clinical and biochemical improvement and was discharged after four days, with a close follow-up appointment scheduled with both the endocrinology and obstetrics outpatient care departments. This case report highlights the necessity of considering hyperthyroidism as a potential etiology in cases of recurrent syncope, especially when clinical signs and symptoms are suspicious of excessive thyroid stimulation, while also reminding clinicians to consider pregnancy as a potential trigger in women of childbearing age.