Hashitoxicosis is the initial hyperthyroid phase of patients with Hashimoto's thyroiditis and, usually, this phase lasts for one to two months. We report a case of a 21-year-old male who had Hashitoxicosis of two years duration before converting to Hashimoto's hypothyroidism. He initially presented with complaints of increased appetite, heat intolerance, fatigue, and sweating. On a physical exam, he had mild exophthalmos with lid lag and a fine tremor in the hands. Thyroid function tests also confirmed that the patient had hyperthyroidism. Thyroglobulin antibody and thyroid peroxidase antibody were both positive. He also had mildly elevated thyroid-stimulating immunoglobulin (TSI) but decreased radioactive iodine uptake scan. Based on the clinical presentation and biochemical test, a diagnosis of Hashitoxicosis was made. This hyperthyroid phase lasted for a period of two years. The patient eventually developed hypothyroidism suggesting that Hashimoto's thyroiditis was the most likely diagnosis. He was started on levothyroxine replacement therapy and remained euthyroid on levothyroxine since that day. The initial presentation mimicked Grave's disease, but with decreased radioiodine uptake, despite the high TSI level, leading us to treat him medically and not with radioactive iodine therapy. The patient was thus spared unnecessary radioactive iodine therapy (RAI) therapy.
Keywords: grave's disease; hashimoto's thyroiditis; hashitoxicosis.