MON-236 - Overlapping Features of Restrictive Eating Disorder and Hyperthyroidism: Lessons from A Case Report

Background: Autoimmune hyperthyroidism can present similarly to restrictive eating disorders (REDs), masking diagnosis, delaying treatment, and complicating management. The intersection between these diagnoses remains unclear. This case presented difficulties with diagnosing and treating autoimmune hyperthyroidism, as complicated by the patient’s previous diagnosis of RED.

Presentation: An 18-year-old female with a history of RED presented to the ER with a recent history of symptomatic hypoglycemic episodes. At presentation, she was severely underweight (35.1 kg, BMI 14.6 kg/m²). Despite compliance with her nutritional plan, it was noted that the patient was not gaining weight. Her home medications included fluoxetine and drospirenone. The patient denied any history of thyroid disease, and thyroid function tests (TFTs) conducted five months prior were normal.

Laboratory results revealed elevated free T4 levels at 3.4 ng/dL and suppressed TSH levels of < 0.2 mIU/L. Sodium, potassium, and chloride levels were low. A thyroid ultrasound was unremarkable. Methimazole 7.5 mg (0.2 mg/kg/day) and atenolol 25 mg/day were initiated. 

After 3 days, her ALT levels increased from 42 U/L to 121 U/L and subsequently to 375 U/L. Similarly, AST levels rose from 26 U/L to 82 U/L and then to 156 U/L. Methimazole was discontinued due to rapid transaminase elevation. While awaiting thyroid antibody results, a thyroid scan revealed a marked diffuse increase in iodine uptake, with a 4-hour uptake of 45.8% and a 24-hour uptake of 57%.

Diagnosis: This patient’s history raised concern for exogenous thyroid hormone intake, as excess thyroid hormone may be misused by patients with RED. Diffuse increased uptake on thyroid scan clarified that the hyperthyroidism was autoimmune in origin rather than exogenous. This reassured us that she was not taking levothyroxine for weight loss. The psychological aspect of her RED presented a challenge in diagnosing hyperthyroidism and may have delayed treatment, which can be dangerous in a high-risk patient. 

Treatment: This patient’s methimazole intolerance prompted thyroid ablation therapy as treatment for her hyperthyroidism. The patient received 12.3 mCi of radioactive iodine. Symptoms of insomnia, tremors, neck pain, diarrhea, and vomiting were relieved by SSKI drops (50 mg BID). Her treatment plan also included behavioral counseling and nutritional guidance throughout. Following completion of the treatment, her TFTs showed free T4 levels of 1.28 ng/dL and TSH levels of < 0.005 mIU/L.

Discussion: Early recognition of autoimmune endocrine pathology in patients with RED is essential, as untreated hyperthyroidism can be life-threatening. Clinically, a comprehensive and multidisciplinary approach should be taken in patients with RED who exhibit atypical findings.

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