SAT477 Consumptive Hypothyroidism In A Patient With Plasma Cell Neoplasm

Disclosure: G. Sidhu: None. I. Madahar: None. A. Haider: None. J. Giordano: None. Introduction: Thyroxine (T4) is converted into metabolically active form triiodothyronine (T3) by deiodinase enzyme 1 & 2 (D1 & D2). Deiodinase 3 converts T4 and T3 into metabolically inactive form reverse T3 (rT3)& di-iodothyronine (T2) . Consumptive hypothyroidism syndrome (CHS) is a very rare form of hypothyroidism seen in patients with neoplasms, which express high levels of D3 enzyme. Case: 68-year-old female withhistory of Multiple Myeloma (MM), POEMS, hyperlipidemia and hypothyroidism was admitted with acute kidney injury, cirrhosis of unclear etiology, large volume ascites and anasarca. She weighed 92 kg on admission. She was complaint with her 50 mcg of levothyroxine and on admission her TSH was 7.14 (N: 0.43-3.55 uIU/ml), Free T4 (FT4): <0.42 (N: 0.7-1.25 ng/dl), total T4 (TT4): 2.6 (N: 4.8-11.7 ug/dl), total T3 (TT3): <20 (N: 80-200 ng/dl). Oral LT4 was switched to IV form due to underlying concerns of malabsorption from anasarca. rT3 was noted to be 40 (N: 8-25 ng/dl). Despite escalated intravenous levothyroxine doses for seven days her FT4, FT3 continued to remain undetectable So her LT4 dose was increased to 75 mcg IV daily initially and eventually to 100 mcg IV daily and 125 mcg daily. On 10(th) day of hospitalization, after her IV LT4 dose was increased to 200 mcg daily, (almost 2.5 mcg/kg/day) her FT4 levels became detectable, 0.50, rT3: 68 and TT3: <20 and TT4: 3.1. Since her rT3 levels were noted to rise after increasing the dose of LT4, liothyronine (LT3) 5 mcg BID was added to her regimen. PET scan showed small sclerotic bone lesions suspicious for active malignancy. Chromogranin A was elevated 313 (N: <311 ng/ml). IR guided biopsy of scapular sclerotic lesion was done and specimen was sent University of Chicago to measure DI-3 activity in the specimen Pathology results were suggestive of plasma cell neoplasm but unfortunately deiodinase activity could not be quantified. Patient developed hepato-renal syndrome during hospitalization and her family decided to pursue hospice care. Discussion: Critical care illness thyroid disease is also associated with increased DI-3 activity and increases rT3, however T4 and TSH are also low in the setting of critical care illness, and most patient do not require supraphysiologic T4 replacements. The presence of D3 in normal tissues such as the brain & placenta has been hypothesized to protect tissues from the effects of excessive thyroid hormone. However, aberrant expression of the enzyme can lead to severe hypothyroidism from inactivation of both endogenously produced and exogenously administered thyroid hormone. Previously this rare syndrome was described in association with massive hemangiomas in children and in a single case of a hemangioendothelioma in an adult. However case reports in adults have been described in nonvascular tumors who required supraphysiologic doses of levothyroxine prior to the resection of a large malignant solitary fibrous tumor. Presentation Date: Saturday, June 17, 2023