THU655 Methimazole Desensitization As An Effective Alternative To Ablation Therapy In Patients With Graves’ Disease Experiencing Thionamide-induced Type IV Hypersensitivity Reactions

Disclosure: J. Arguinchona: None. A. Mahajan: None. A. Gonzalez-Estrada: None. E. De Filippis: None. Introduction: Patients with newly diagnosed Graves’ disease often choose treatment with methimazole (MMI) over traditional ablation therapies. However, MMI can result in adverse reactions including skin rash, pruritus, and urticaria. We present a case of Graves’ thyrotoxicosis with a type IV hypersensitivity reaction while on MMI. The patient was successfully treated with a novel, individualized, 27-day desensitization protocol which resulted in tolerance of MMI with subsequent improvement in thyroid indices. Clinical Case: A 42-year-old female presented for abnormal thyroid studies with associated insomnia, heat intolerance, palpitations, resting tremor, and weight loss. Lab work revealed a thyroid-stimulating hormone <0.005 (0.450-4.500 μIU/mL), free thyroxine 3.28 (0.82-1.77 ng/dL), triiodothyronine 310 (71-180 ng/dL), thyroid peroxidase antibody (Ab) 62 (0-34 IU/mL), thyroid-stimulating immunoglobulin 0.67 (0.00 -0.55 IU/L), and thyrotropin receptor Ab of 6.00 (0.00-1.75 IU/L). She was started on MMI, 10 mg daily for Graves’ disease. Three weeks later, T3 and T4 remained elevated prompting an increase in MMI dose to 10 mg twice daily. Two weeks later, she developed a diffuse, pruritic maculopapular exanthema over her trunk, neck, and extremities. Methimazole was discontinued while prednisone was initiated that subsided her rash. Unfortunately, the patient’s symptoms recurred upon repeat MMI exposure. The patient declined propylthiouracil due to concerns of hepatotoxicity and elected to avoid ablation therapy with iodine or surgery. With the assistance of an allergist, a novel, 10-step, 27-day desensitization protocol was developed specifically for her reaction to MMI with plans to taper prednisone once desensitization was completed. The patient underwent desensitization with development of mild lower extremity exanthema that was successfully treated with high dose antihistamines. Three months later, she was tolerating MMI at 15 mg daily without further adverse reactions and tapered off prednisone. While on MMI, her immune titers normalized with euthyroid clinical and biochemical restoration. Conclusion: Many patients and clinicians initially prefer medical management over definitive ablation therapies in the treatment of Graves’ disease. This case demonstrates with the assistance of an allergist, desensitization to MMI is a viable option in the setting of a known hypersensitivity reaction when it is the first line treatment and no equally efficacious alternatives exist. In addition, patient’s preferences should also be considered during medical decision making. Previous literature has offered various rapid desensitization protocols for MMI for immediate type hypersensitivity reactions. However, in non-immediate, type IV hypersensitivity reactions, a slower desensitization protocol can be considered, as demonstrated in this case. Presentation: Thursday, June 15, 2023