Abstract Disclosure: N. Hasan: None. D. Yang: None. T. Othman: None. J. Dai-Ju: None. Background: Most cases of Myxedema Coma are associated with primary hypothyroidism with significantly elevated TSH levels. However the presence severe illness can contribute to decreased TSH release even in the absence of central lesions. Case: 60 year old female was found down covered in feces. She was hypothermic to 89°F, with a pulse of 62. Physical exam revealed hair loss, thick tongue, non-pitting edema, and delayed relaxation of brachial reflexes. Labs showed Sodium of 123, blood glucose of 80. Thyroid function testing revealed only a mildy elevated TSH of 13 with free T4 <0.025. Anti-TPO antibodies were elevated at 157. MRI of the Sella was negative any lesions. Thyroid ultrasound showed atrophic bilateral thyroid lobes. Assessment for hypopituitarism did not show any significant deficiencies with Cortisol 45, ACTH 11, LH 0.5, FSH 8.5, IGF-33, and Total Testosterone 10. She was found to have septic shock secondary to perforated sigmoid colon requiring colectomy. She was initially loaded with Dexamethasone 4mg followed by IV Levothyroxine 100mcg, with steroids being discontinued after AI was ruled out. After treating her sepsis she was transitioned to 150mcg of oral Synthroid with improvement of her thyroid function tests to TSH of 2.7 and free T4 of 1.56. Discussion: The majority of Myxedema Coma is associated with primary hypothyroidism. In these cases, TSH levels are markedly elevated, often greater than 100. When the TSH is not as elevated as we would expect, many factors must be considered, the greatest being central hypothyroidism where TSH secretion may be impaired from pituitary tumors, surgery, radiation, and other causes. Our patient however did not have any central lesions on imaging and was found to have anti TPO antibodies with atrophic thyroid lobes on ultrasound suggestive of primary hypothyroidism. This brings us to the effect of acute illness on the balance of thyroid hormones. Conditions such as sepsis stimulates elevations in inflammatory cytokines which disrupt the physiologic response to release TSH. Previous studies involving sepsis revealed the main cytokines implicated are TNF alpha, Interferon gamma, IL-1, and IL-6. The degree of inadequate TSH secretion is often times proportional to the severity of illness and improves after recovery from the illness. Conclusion: Our body's response to critical illness involves complex hormonal changes which affect the HPA axis and can decrease TSH secretion, even in myxedema coma without central lesions. Presentation: 6/1/2024