SAT-424 From Hypothyroidism to the Adrenal Crisis: A Rare Case of Isolated Secondary Adrenal Insufficiency

Abstract Disclosure: A. Yousef: None. C. Xue: None. A. Shehadah: None. L. Chavez: None. Isolated secondary adrenal insufficiency is a rare disorder characterized by low or absent adrenocorticotropic hormone (ACTH), resulting in impaired cortisol production while sparing other pituitary hormones. It is often misdiagnosed due to nonspecific symptoms, increasing the risk of complications. We present a case of a 61-year-old man with prediabetes who presented to his primary care physician with a two-month history of fatigue, generalized weakness, and unintentional weight loss of 25 pounds. His symptoms were associated with nonspecific complaints of blurry vision, myalgias, constipation, and arthralgias. Initial laboratory evaluation showed a mildly elevated TSH of 5.58 μIU/mL (normal: 0.5-4 μIU/mL) and decreased free T4 of 0.6 ng/dL (normal: 0.8-1.8 ng/dL), while anti-TPO antibodies were negative. Based on these findings, he was diagnosed with hypothyroidism and started on 50 mcg levothyroxine therapy, which was later increased to 75 mcg. Despite treatment, his symptoms persisted, prompting him to seek care in the emergency department (ED). In the ED, he was noted to be hypotensive, and laboratory studies revealed eosinophilia of 12% (normal: 0-3%), normal electrolytes, low TSH with normal free T4, normal levels of LH and prolactin, and a low morning cortisol level of 2.0 μg/dL (normal: 5-25 μg/dL). Due to suspicion of adrenal crisis, hydrocortisone therapy was initiated, and his home levothyroxine dose was reduced. Imaging, including an abdominal CT scan, demonstrated normal adrenal glands, and an MRI of the head revealed a normal pituitary gland. Further blood work confirmed a low ACTH level of 8.7 pg/mL (normal: 10-60 pg/mL). The patient was discharged on hydrocortisone therapy, which resulted in significant improvement in symptoms. Notably, treatment with levothyroxine can exacerbate adrenal insufficiency, as elevated TSH may sometimes be a feature of adrenal insufficiency. This case highlights the importance of keeping a broad differential, and performing a thorough evaluation to avoid misdiagnosis and prevent precipitating factors for adrenal crisis. Presentation: Saturday, July 12, 2025