PSAT253 Differentiation of Pituitary Hyperplasia From Adenoma in the Setting of Severe Hypothyroidism

INTRODUCTION: Pituitary hyperplasia due to long-standing or profound primary hypothyroidism is a rare finding in children. It occurs because of constant stimulation of thyrotrope cells by a thyrotropin-releasing hormone secreted from the hypothalamus due to a lack of negative feedback from thyroid hormones. The clinical presentation and imaging can mimic a pituitary mass. Patients can present with features of hypothyroidism, hyperprolactinemia, and even visual field defects if the hyperplastic pituitary gland compresses the optic chiasm. This case highlights this uncommon finding and discusses subtle clinical signs of hypothyroidism in children. CASE PRESENTATION: A 10-year-old boy was incidentally found to have a pituitary lesion (15 mm×14 mm) when an MRI of the brain was performed as a healthy volunteer screening procedure. History and physical exam revealed cold intolerance, lack of height growth for 2 years (crossing down from 75th to 25th percentile), and dry skin with the barely palpable thyroid gland. There was no family history of thyroid or auto-immune disease. Evaluation of pituitary hormones showed remarkably high thyroid-stimulating hormone (>500 mcIU/ml) in the setting of undetectable free thyroxine, positive thyroid peroxidase antibody, low insulin-like growth factor-1, mildly elevated prolactin (67.4 mcg/L), and mild macrocytic anemia. CONCLUSIONS: Differentiation of pituitary hyperplasia from pituitary hormone-secreting or non-secreting adenomas is crucial, as the primary modality of treatment of pituitary hyperplasia secondary to primary hypothyroidism is thyroid hormone replacement and not surgery unless the patient has visual field defects necessitating of decompression of the optic chasm to avoid permanent vision loss. In general, pituitary hyperplasia is described as homogeneously enhancing with the "nipple sign," which is when the pituitary gland has smooth contours, but a central protrusion of a pituitary mass is present. Elevated TRH can also lead to lactotroph hyperplasia, causing increased prolactin. Growth hormone secretion may be reduced by hypothyroidism and/or by damaged somatotroph cells due to space-occupying pituitary hyperplasia. Macrocytic anemia has been reported in patients with hypothyroidism and is thought to be an adaptation to a decreased basal metabolism. Early recognition and treatment of hypothyroidism during childhood is essential for normal growth and development. In children with the prolonged disease, final height may be compromised, and academic performance and psychosocial well-being may decline. Gradual replacement of thyroid hormone to therapeutic doses by slowly escalating doses of levothyroxine may be beneficial to prevent complications of therapy such as pseudotumor cerebri or empty sella due to rapid shrinkage of lactotroph and thyrotrope cells. Previous studies have shown approximately 85% of those with pituitary hyperplasia due to primary hypothyroidism demonstrate decreased pituitary gland size after starting thyroxine replacement and recommend repeating pituitary MRI after 2-4 months. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.