FRI557 Don’t Forget The Incidental Thyroid Nodule In Graves’ Disease. A Case of Marine-Lenhart Syndrome

Disclosure: K.N. Andino-Lebrón: None. A. Martinó-Morales: None. J.M. Colón-Castellano: None. Marine-Lenhart syndrome (MLS) was initially described by Charkes in 1972 as he observed patients with Graves’ disease (GD) and incidental functioning thyroid nodules. He named the disease Marine-Lenhart syndrome based on a paper published by Marine and Lenhart in 1911. MLS is a variant of GD now described as the coexistence of GD and autonomous functional thyroid nodules (AFTN); thus, patients present with thyrotoxicosis due to GD and AFTN. MLS is very rare, and prevalence is estimated to be around 0.8%-2.7%. Here, we present a case of MLS in a 79-year-old female. A 79-year-old Hispanic woman with history of breast metaplasia s/p chemoprevention with tamoxifen for 5 years, atrial premature contractions on metoprolol, among other medical conditions was referred to Endocrinology clinics by her primary care physician (PCP) because of abnormal thyroid function tests and ultrasound. She reported feeling anxious with associated palpitations, she denied weight loss. Physical examination was remarkable for regular rate and rhythm, no goiter, no palpable nodules, no proptosis, and deep tendon reflexes +1. Laboratory testing revealed a suppressed TSH of 0.224 uIU/mL, normal free T4 at 1.17 ng/dL, normal total T3 at 142.5 ng/dL, and positive thyroid stimulating immunoglobulins at 345%. Thyroid ultrasound showed a normal size gland with multiple complex nodules. In the right lobe there was a mixed cystic and solid nodule, measuring 1.48x1.21x1.71cm, wider than tall, with internal vascularity and punctate calcifications. In the left lobe there was an isoechoic and solid nodule measuring 0.7x0.5x0.7cm, wider than tall, without calcifications. Thyroid uptake scan with SPECT-CT demonstrated a focus of increased tracer uptake on the upper pole of the right thyroid lobe that corresponds to the one found on CT scan and a diminished and nonuniform uptake of the tracer in the reminders of the thyroid gland. The 24-hour radioactive iodine uptake was 17.5%. Diagnosis of MLS was made, and the patient was started on methimazole 5mg daily, which she has been tolerating well. Follow up laboratories show a biochemically euthyroid state. Marine-Lenhart syndrome is a rare entity of Graves’ disease which is currently defined as GD and accompanying functioning nodule(s). To establish the diagnosis, it is important the evaluation with scintigraphy and autoimmune testing. Multiple treatment options are available and patients with GD should be evaluated for the presence of thyroid nodules and their functional status to achieve optimal therapy. Patients with GD have a chance of remission when treated with antithyroid drugs. Due to the pathophysiology of AFTN, patients with MLS (concurrent GD and AFTN) have lower remission rates with antithyroid drugs and may require definitive management therapy with radioactive iodine or surgery. Presentation: Friday, June 16, 2023