PMON322 Gigantism in 13-Year-Old Male With Pituitary Tumor

BACKGROUND: Pituitary gigantism is caused by excess growth hormone [GH] secretion from the pituitary gland when the growth plates are open leading to excessive linear growth and tall stature in the pediatric population. It is extremely rare with a reported incidence of 8 cases per million person-years. CLINICAL CASE: The patient is a 13-year-old male who presented with concerns of accelerated growth rate and tall stature. His father noticed the patient's tall stature when he passed his own height the last year. The patient was seen by his PCP who referred the family to pediatric endocrinology. His symptoms included snoring and bi-weekly headaches, but no vision changes. Review of his growth charts showed linear growth tracking at greater than the 95th percentile since the age of 9 years. His clinical features included large hands, large feet, prominent jaw, testicular volume >25 ml, tall stature [Ht > 99%, Z= +4.59 SD]. The patient's mid-parental height is 69.1 inches [175.5 cm] and the patient measured 76.6 inches [194.5 cm]. His predicted height was 7 feet 1.5 inches [217.2 cm] based on his bone age. His clinical features were strongly concerning for Gigantism. Initial labs showed IGF-1 of 924 ng/mL [168–576], prolactin of 20.1 ng/mL [2.8–11.0], and IGF-BP3 8.7 mg/L [3.1–9.5]. Cortisol, ACTH, TSH, FT4, LH, FSH, Testosterone were within normal limits. Bone age was concordant with chronological age. MRI showed enlarged pituitary gland measuring 1.3 cm in height, suspicious for macroadenoma. Cardiac evaluation including echocardiogram came back normal. GH suppression test resulted in a 2-hour GH level of 27.3 ng/mL [<1] and he was diagnosed with Gigantism due to GH-secreting pituitary tumor. The parents decided to consult neurosurgery team at a different facility, where transsphenoidal resection of the pituitary tumor was performed. He did not develop any postoperative complications, including Diabetes insipidus or any pituitary hormone deficiencies, and was discharged home shortly after. Follow-up MRI of the pituitary showed no evidence of residual tumor. Pathology of the macroadenoma expressed GH and prolactin on immunohistochemical stains and was negative for TSH, LH/FSH, and ACTH. Genetic studies obtained were negative, lowering the likelihood of inherited predisposition to endocrine neoplasms. The patient has remained well post-operatively and has been able to continue school and play basketball without issues. CONCLUSION: Pituitary gigantism occurs in the pediatric population prior to skeletal epiphyseal closure and is caused by GH excess. Initial screening tests should evaluate for pituitary function including IGF-1 and prolactin levels. The gold standard for diagnosing GH excess is the GH suppression test. Even though rare, it is important for clinicians to keep a high level of suspicion for quick recognition and management of overgrowth syndromes. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.