New-Onset Primary Hypothyroidism in a 14-year-old Girl Presenting as Hemorrhagic Shock From Severe Menorrhagia.

Hypothyroidism can lead to menstrual irregularities due to its effects on the hypothalamic-pituitary-ovarian axis. Considering this correlation, we present a case of a 14-year-old female in critical condition with hemorrhagic shock from menorrhagia. Initial workup discovered severe anemia with a hemoglobin of 1.8 g/dL (18 g/L) (reference range, 12.0-15.0 g/dL; 120-150 g/L) and profound primary hypothyroidism with a TSH level of 423.7 μU/mL (423.7  mIU/L) (reference range, 0.40-4.2  mIU/mL) and an undetectable free thyroxine of <0.2 ng/dL (<2.5 pmol/L) (reference range, 0.6-1.5 ng/dL; 7.7-19.3 pmol/L). This was confirmed on repeat laboratory testing along with an elevated thyroid peroxidase antibody level of 19.6 IU/mL (reference range, 0.0-9.0 IU/mL) and elevated antithyroglobulin antibody level of 5.0 IU/mL (reference range, 0.0-4.0 IU/mL). She was diagnosed with primary hypothyroidism from autoimmune thyroiditis. Even with blood transfusions, her heavy menstrual bleeding persisted. Thyroid hormone replacement therapy was initiated with oral levothyroxine 50 μg (0.84 μg/kg) once daily, along with high-dose combined oral contraception, with clinical improvement. This severe case presentation illustrates the link between menorrhagia and hypothyroidism in pediatric populations, highlighting the need to address this association in adolescents and ensure optimal care for these patients.