SUN-356 - Rapid Regression of Pituitary Hyperplasia in Primary Hypothyroidism Following Levothyroxine Therapy

Background: Pituitary hyperplasia secondary to longstanding untreated or undertreated primary hypothyroidism is a recognized yet uncommon phenomenon. However, the expected timeline for radiographic regression remains poorly defined, and recommendations for repeat imaging following levothyroxine replacement are undetermined, particularly with suprasellar extension and visual involvement.

Case: A 23-year-old female with Hashimoto’s hypothyroidism presented with worsening cold intolerance, myalgias, and weight gain. Thyroid function testing revealed a TSH of 461.7 µIU/mL (normal 0.4 - 4 µIU/mL), undetectable free T4, and low free T3 of 1.52 pg/mL (normal 2.0-4.4 pg/mL). She reported adherence to a weekly Tirosint regimen. She had a similar hospital admission six months earlier; levothyroxine absorption test was performed then with appropriate response; EGD revealed no evidence of malabsorption.

IV levothyroxine was initiated. Due to recent dental infection, a neck CT was obtained which incidentally revealed an enlarged pituitary gland with suprasellar extension. MRI revealed diffuse enlargement and homogenous enhancement of the pituitary gland with suprasellar extension and increase in perfusion suggesting hypervascularity, suspicious for pituitary hyperplasia, measuring 20 mm (transverse) x 8 mm (antero-posteriorly) x 12 mm (craniocaudal). Abutment of the optic chiasm was noted. Humphrey visual fields revealed temporal depression in both eyes. Remainder of hormone evaluation was unremarkable except for prolactin of 117 ng/mL (norm 5 - 26 ng/mL). Weekly in-office levothyroxine administration was arranged for the next 6 weeks, with rapid improvement in thyroid function testing and symptomatology. TSH normalized to 1.09 µIU/mL after 3 weeks. As part of evaluation with an outside provider, an MRI was obtained six weeks after the first consistent levothyroxine administration; this revealed ongoing heterogeneity of the gland, however now measuring 8.7 mm craniocaudally and without mass effect upon the optic chiasm.

Conclusion: Although the optimal timing for repeat imaging of pituitary hyperplasia in primary hypothyroidism is unknown, this case highlights rapid radiographic regression after just 6 weeks of consistent levothyroxine administration in a young and otherwise healthy female. These findings suggest that early repeat imaging may be considered in select patients and support conservative management with levothyroxine replacement in a monitored fashion.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*