SAT-471 A Rare Case of Pretibial Myxedema Preceding Graves’ Hyperthyroidism

Introduction: Pretibial myxedema, also known as thyroid dermopathy, is typically seen as a manifestation of long-standing Graves’ disease. We report a rare case of pretibial myxedema as the initial presentation of Graves’ disease in a patient without ocular or overt hyperthyroid symptoms. Case: The patient is a 68 year old male with a past medical history of type 2 diabetes and hypertrophic cardiomyopathy, presenting with a one year history of a mildly pruritic, violaceous plaque of his left shin. He was referred to Dermatology Clinic, and biopsy came back as pretibial myxedema. Of note, his thyroid function studies were normal 6 months prior, and he had no symptoms of active thyroid disease at presentation. Additionally, he did not have any ocular abnormalities on exam. Upon repeat laboratory studies, he had low but detectable TSH, normal free T4, mildly elevated free T3, and elevated TSI/TRAb, overall consistent with early Graves’ hyperthyroidism. His pretibial myxedema was treated with high-dose topical steroids with improvement of his dermopathy. For his hyperthyroidism, he was started on low dose methimazole and never developed Graves’ ophthalmopathy. Discussion: Although the exact pathophysiology of pretibial myxedema is unknown, it is thought to be mediated by TSH receptor expression on fibroblasts, similar to Graves’ ophthalmopathy. It is usually seen in patients with active or longstanding Graves’ disease, often with high levels of thyroid receptor antibodies and concomitant Graves’ ophthalmopathy. However, there are a few cases of pretibial myxedema occurring in euthyroid patients with or without ocular symptoms, usually in the setting of elevated TSI, TRAb, or TPO antibodies. Our patient is a rare case of pretibial myxedema preceding active thyroid disease without ophthalmologic manifestations. Patients with hyper-pigmented, non-pitting plaques or nodules on pretibial regions should prompt providers to consider pretibial myxedema and test for thyroid studies, even in those without symptoms of hyperthyroidism or Graves’ ophthalmopathy.