THU026 Severe Insulin Resistance In Type 1 Diabetes Due To Growth Hormone Producing Pituitary Macroadenoma

Disclosure: R. Pansare: None. D. Khurram: None. L. Folsom: None. Background: Acromegaly is a rare disorder with an incidence ranging from 28 to 137 per million. Elevated IGF-1 in acromegaly is associated with severe insulin resistance and diabetes mellitus in the absence of visceral adiposity. We present a case of acromegaly identified in a lean individual with type 1 diabetes with progressive, severe insulin resistance requiring U-500 insulin via insulin pump. Clinical Case: A 28-year-old individual with type 1 diabetes mellitus diagnosed at age 17 years, hyperlipidemia, PCOS, rheumatoid arthritis, depression, and fibromyalgia presented with symptoms of brain fog, fatigue, functional decline, and nocturnal hyperhidrosis. Vital signs obtained in endocrinology clinic revealed blood pressure 100/70 mmHg and BMI 27 kg/m2. Glycemic control was suboptimal with HbA1c ranging from 7.5-9.5% over the past 2 years. The patient had developed progressive insulin resistance with subsequently increased insulin needs, ultimately requiring U-500 insulin administered via insulin pump. Brain MRI ordered due to additional symptoms revealed a sellar mass. Dedicated pituitary MRI confirmed a 2.1 cm anterior pituitary macroadenoma with compression of the optic chiasm, without cavernous sinus invasion. Biochemical evaluation at 9:57am revealed elevated IGF-1 801 ng/ml (93 - 297), Z-score +5.1. Additional testing revealed ACTH 17.9 pg/ml (7.2 - 63.3), cortisol 9.6 mcg/dl (3.7 - 19.4), TSH 0.741 mIU/L (0.27 - 4.2), free T4 1.32 ng/dl (0.93 - 1.7), prolactin 8.4 ng/ml (5.2 - 26.5), leptin 14.4 ng/ml (0.5 - 15.2), LDL 151 mg/dl (0 - 100), triglycerides 203 mg/dl (0 - 149). The patient subsequently underwent transsphenoidal resection of the pituitary macroadenoma. Discussion: Diabetes mellitus in acromegaly is associated with increased mortality. When elevated, IGF-1 level has been shown to be an independent predictor for risk of development of diabetes mellitus in acromegaly and correlates with insulin resistance. A unique challenge arises when the diagnosis of acromegaly is suspected in existing uncontrolled diabetes, as IGF-1 levels may be elevated, normal, or low. Post-surgical reduction in serum IGF-1 level is associated with early postoperative improvement in glucose tolerance. As such, once the diagnosis is confirmed, prompt surgical intervention is imperative to decrease this risk, as well as to improve hyperglycemia and decrease insulin requirements. Although de novo type 2 diabetes in acromegaly is common, our case is novel as it highlights the need to expand the differential diagnosis to include exogenous causes for progressively worsening insulin resistance in individuals with type 1 diabetes. Presentation: Thursday, June 15, 2023