MON-065 An Interesting Case of Acromegaly With a Normal IGF-1

Abstract Disclosure: M.B. Herrera Gonzalez: None. P. Savani: None. M. Bilbatua: None. Background Acromegaly arises from the persistent overproduction of growth hormone (GH), which stimulates the liver to secrete insulin-like growth factor-1 (IGF-1). IGF-1 is primarily responsible for the clinical manifestations of acromegaly. Measuring serum IGF-1 levels is the most reliable single test for diagnosing acromegaly. Here, we present a case of a patient with a pituitary microadenoma and clinical features of acromegaly, yet exhibiting normal IGF-1 levels. Case presentationA 52-year-old male with history of Decompensated Hep C Cirrhosis and Insulin-Dependent type 2 Diabetes Mellitus (IDDM) with HbA1C of 9.3%, presented to the endocrinology clinic for evaluation and treatment of DM. On physical examination, the patient exhibited prognathism, enlargement of nose and hands and a deep, hoarse voice. Three years prior, he was diagnosed with a pituitary microadenoma of 0.6 mm. Current endocrine tests showed Cortisol 13 ng/ml (3-20 ng/ml), prolactin 34 ng/ml (2-18 ng/ml), IGF-1 of 113 ng/ml (50-317 ng/ml), Total testosterone 450 ng/dL (264-916 ng/dL), ACTH 43 pg/mL (10-60 pg/mL). The patient’s diabetes regimen was adjusted, and a continuous glucose monitor was placed. At the follow-up visit, his glucose management indicator improved to 7%, and repeated IGF-1 resulted within normal limits. Given the patient's history of liver cirrhosis, we obtained a glucose GH suppression test. Baseline GH of 3.2 µg/L (< 2µg/L), and a 2-hour post-oral glucose tolerance test (OGTT) level of 7.5 µg/L after the administration of 75 grams of glucose, diagnostic for acromegaly. The patient underwent uncomplicated transsphenoidal endoscopic pituitary resection. Post-op tests showed prolactin 15 ng/mL, cortisol 11 ng/mL and GH suppression test 1 µg/L. Discussion: Acromegaly features primarily result from excess growth hormone (GH); however, acromegaly is fundamentally a biochemical diagnosis and does not require the presence of overt physical characteristics or visible pituitary tumors on MRI. The most reliable diagnostic test is serum insulin-like growth factor-1 (IGF-1), as its levels reflect overall GH activity and remain unaffected by daily GH fluctuations. Elevated IGF-1 levels are highly sensitive for acromegaly, while normal levels strongly argue against the diagnosis. Nevertheless, conditions such as liver and kidney dysfunction, hypothyroidism, malnutrition, and oral estrogen use can lower IGF-1 levels, causing false negative diagnoses. While the GH suppression test can provide definitive evidence, it is often unnecessary when clinical features and imaging findings of a pituitary adenoma are present. However, it serves as a valuable test in cases where IGF-1 levels are misleading. Presentation: Monday, July 14, 2025