THU666 Should We Think About Thyroid Disease In A Patient With Thymoma Related Myasthenia Gravis?

Disclosure: G. Wintermyer: None. E. Villanueva: None. Oftentimes, Graves and Myasthenia Gravis present with very similar symptoms. This can complicate diagnoses of either. At the same time, Graves can cause thymic hyperplasia, and there is a link between Myasthenia Gravis and thymoma. In the following, we discuss a case that presented all three: 59-year-old female with PMHx of hyperlipidemia, GERD, hoarseness, and anxiety developed a sudden diplopia, unintentional weight loss, tremor, palpitation, and ptosis for approximately one week. She had an eye exam and was recommended to have an MRI/MRA of brain and new blood work including CBC, CMP, TSH, Free T4, T3, Acetylcholine receptor antibody, and ANA. TSH came back suppressed and undetectable, Free T4 6.4ug/dL and T3 40 ug/dL. ANA and Acetylcholine receptor antibody were both high. Later, Anti-TPO and TSI measured 235 IU/mL and 34.5 IU/L respectively. Also, due to high concern for stroke given her symptoms, patient had ED visit. While having stroke workup in ED, her CTA of the neck revealed incidental finding of mediastinal mass that was concerning for possible thymoma. Stroke was ruled out. Patient was referred to our endocrinology clinic for her thyrotoxicosis. She was started on Methimazole 30 mg daily and Propranolol 60 mg daily. In the meantime, patient started to see neurologist for her Myasthenia Gravis. The neurologist started her on Prednisone 5 mg daily and Pyridostigmine60 mg daily. She was also referred to thoracic surgery for mediastinal mass resection. She received lugol 7 days prior to surgery to prevent intraoperative thyroid storm. Patient successfully had the surgery, and the mass was removed. The result was thymic hyperplasia. She was clinically well after surgery, though her ocular symptoms worsened by tapering steroids. Patient also had trial of plasma exchange which helped with her ocular symptoms. Her hyperthyroidism symptoms and thyroid function improved. She gradually was able to take a lower dose of methimazole. Patient currently is on Methimazole 5 mg without any complications. Clinicians are advised to always rule out any possibility of thyroid disease in patients that are suspicious for Myasthenia Gravis especially if Myasthenia Gravis is secondary to thymoma. Neglecting thyroid diseases in this group can cause serious consequences including intraoperative thyroid storm. Also, by early diagnosis of both Myasthenia Gravis and hyperthyroidism, there will be a better and faster resolution in patients’ symptoms. Presentation: Thursday, June 15, 2023