THU226 Pituitary Hyperplasia With Optic Chiasm Compression Secondary To Levothyroxine Non-adherence In An Adolescent Patient

Disclosure: C. Hawco: None. L. Bursztyn: None. P. Gallego: None. S. Van Uum: None. Background: Pituitary hyperplasia is a rare complication of primary hypothyroidism in pediatric patients. There have been multiple reports of unnecessary surgical procedures for this medically treatable condition. Clinical Case: A 16-year-old female was referred for pituitary enlargement. She had presented to a community hospital following an unwitnessed syncopal event, complicated by retrograde amnesia and headache. At the age of 2 she was diagnosed with primary hypothyroidism during work up for similar syncopal episodes. Past medical and developmental history was otherwise non-contributory. She had a long-standing history of medication non-compliance, and had not taken Levothyroxine during the previous 11 months. On her presentation to hospital, a CT scan revealed pituitary enlargement with a hypodensity suspicious for hemorrhage. Pituitary panel was significant for TSH greater than 1000 (0.51-4.30) mIU/L, free T4 of 4 (13-21) pmol/L and Prolactin 98 ng/mL (&lt25) ng/mL. She was subsequently transferred to our tertiary care pediatric hospital for admission and ongoing care. An MRI of the sella identified a 1.0 x 2.3 x 1.7 cm pituitary mass with suprasellar extension and mass effect on the optic chiasm and nerves. There was no associated hemorrhage. The thyroid gland was diffusely enlarged. Visual acuity was 20/60 in both eyes at the time of hospital admission, compared to 20/20 the previous week at her optometrist. Formal visual field testing was abnormal, but unreliable with no clear defects. She was initiated on Levothyroxine 100 mcg daily and closely monitored for adherence and symptom resolution. After two months on this dose, repeat MRI sella showed a decrease of the pituitary mass to 0.8 x 2.1 x 1.0 cm in size, consistent with a diagnosis of pituitary hyperplasia secondary to untreated primary hypothyroidism. After treatment for 3 months, her visual acuity returned to 20/20 in both eyes with normal visual fields. With ongoing adherence to medical therapy, she remained clinically euthyroid with further decrease in her pituitary size, and normalization of both thyroid indices and prolactin[SV1]. Conclusion: This case is a rare presentation of pituitary hyperplasia in the setting of treatment nonadherence in primary hypothyroidism. It emphasizes the importance of monitoring for signs and symptoms of pituitary enlargement when low or non-adherence for levothyroxine treatment is suspected. The resolution of pituitary enlargement with Levothyroxine treatment also reinforces that this condition is best managed medically, avoiding unnecessary surgical procedures. Reference: (1) Sapkota, S., Karn, M., Sapkota, S. Pituitary hyperplasia in childhood primary hypothyroidism: a review. Childs Nerv Syst. 2021;37;749-762. [SV1] Presentation: Thursday, June 15, 2023