FRI548 A Case Of Periureteric Myxedema

Disclosure: J.M. Ferris: None. J. Merrimen: None. S.M. Kaiser: Advisory Board Member; Self; Amgen Inc. Speaker; Self; Amgen Inc. Background: Graves’ disease is the most common cause of hyperthyroidism. Classic extrathyroidal manifestations include Graves orbitopathy and pretibial myxedema (also known as thyroid dermopathy). Both involve cytokine-induced hyaluronic acid secretion by fibroblasts, likely related to TSH-receptor antibodies. Pretibial myxedema is now rare, but nearly always coexists with orbitopathy. It classically involves the shins, but has been described in other locations. Here we present a case of myxedema changes affecting the periureteric soft tissue of a patient with Graves’ disease. Case: A 46-year-old male was seen by endocrinology for symptomatic hyperthyroidism. His clinical presentation was consistent with Graves’ disease and the diagnosis was confirmed with a strongly positive TSH receptor antibody of 25 IU/L (normal <1 IU/L). He had findings of moderate thyroid eye disease and had bilateral skin changes suspicious for pretibial myxedema. The skin findings preceded his hyperthyroidism by a few years. Dermatology was consulted and a skin biopsy confirmed pretibial myxedema, which was treated with triamcinolone injections with good effect. His thyroid function normalized with methimazole. Coincidentally, while being treated for Graves’ disease he altruistically donated a kidney to a transplant recipient. During the nephrectomy, it was noted that part of the periureteric tissue appeared thickened and firm, and further dissection revealed a soft tissue, lipoma-like mass surrounding the ureter. A frozen section sent from the operating room was found to contain myxomatous adipose tissue with very little cellularity. The final pathology reported adipose tissue with myxoid degeneration and reactive lymphoid aggregates. The histomorphology was consistent with a reactive process and there was no evidence of malignancy. In the context of the patient’s history the findings were concluded to be related to his Graves’ disease. Discussion: While pretibial myxedema most commonly affects the shins, it has also been described at other dermatologic sites, often associated with areas of trauma. Our patient, who had biopsy proven thyroid dermopathy, was also found to have myxedema affecting the ureter. To our knowledge this is only the third reported case of ureteral myxedema, and the first in a kidney donor. The patient’s renal function before surgery was normal, and post-nephrectomy his eGFR is mildly decreased, but stable. His thyroid function remains normal on methimazole. Presentation: Friday, June 16, 2023