ODP399 Growth Hormone Peak did not predict presence of Pituitary Stalk Interruption Syndrome

BACKGROUND: Pituitary stalk interruption syndrome (PSIS) is a congenital abnormality of the pituitary gland characterized by a triad of the thin or interrupted pituitary stalk, aplasia, or hypoplasia of the anterior pituitary and absent or ectopic posterior pituitary. This can be associated with midline defects and pituitary endocrine deficiencies, ranging from isolated growth hormone deficiency to combined pituitary hormone deficiency. PSIS is a rare entity with an estimated incidence rate of 0.5/1,000,000 births. Clinical case: A 3-year-old neurodevelopmentally appropriate male was initially seen at the PCP office for growth failure. After birth, the patient appeared to have normal growth parameters, as he was in the 61st percentile for length and at the 19th percentile for weight. His growth velocity trended downwards, as he dropped to the 34th percentile at nine weeks old and the 2nd percentile by nine months old. PCP records showed that the patient was at the 10th percentile for height at one year old, but by 18-months, he had fallen below the 1st percentile. His mid-parental height was 175cm, between 25th and 50th percentile. Initial workup showed elevated TSH 9.12 mIU/ml (0.5-4.3 mIU/mL) with negative thyroid antibodies, thus started on 25 mcg of levothyroxine. The screen for systemic disease and inflammatory markers was negative. Insulin-like growth factor 1 (IGF-1) was low at <16 ng/mL (24-148 ng/mL) and insulin-like growth factor binding protein-3 (IGFBP-3) was normal at 1.2mcg/ml (0.7-3.6)A growth hormone (GH) stimulation test was obtained due to suboptimal growth, short stature, and undetectable IGF-1 level. The patient failed his GH stimulation study with a GH peak of 5.1 ng/mL (>10) after clonidine and 2ng/ml (>10) after arginine. A clinical and biochemical diagnosis of GHD was made, an MRI was ordered to evaluate for anatomic cause. Brain MRI showed an ectopic posterior pituitary gland with an absent infundibulum, suggesting PSIS. The patient was started on GH therapy with excellent response. He is currently growing well on a low dose of somatropin, around 0.234mg/kg/week. CONCLUSION: PSIS is a congenital pituitary anatomical defect with a heterogeneous presentation. It is typically encountered in infancy and childhood, possibly progressing to panhypopituitarism by adulthood. Diagnosis can be delayed, as brain MRI imaging is not always obtained based on growth hormone peaks. As seen in our patient, the severity of GHD based on peak levels did not adequately predict the presence of brain anomalies. Historically, severe GHD (<5 ng/mL) is strongly associated with brain MRI abnormalities, but GH levels may not suffice to determine the severity of the disease. Based on our findings, we recommend obtaining brain MRI in all patients diagnosed with GHD to identify critical anatomical abnormalities, like PSIS, that require long-term close monitoring of pituitary function. Presentation: No date and time listed