Long-Term Follow-Up of a Child with Autoimmune Thyroiditis and Recurrent Hyperthyroidism in the Absence of TSH Receptor Antibodies

Hashitoxicosis is an initial, transient, hyperthyroid phase that rarely affects patients with Hashimoto thyroiditis. We present here an unusual case of a child with Hashimoto thyroiditis and recurrent hyperthyroidism. A 4 yr 6/12 old male was diagnosed by us with autoimmune subclinical hypothyroidism (normal free T4, slightly elevated TSH, and elevated TG antibody titer). Two years and 6/12 later he experienced increased appetite and poor weight gain; a laboratory evaluation revealed suppressed TSH, elevated free T4, and normal TSI titer. In addition, an I 123 thyroid uptake was borderline-low. A month later, the free T4 had normalized. After remaining asymptomatic for 3 years, the patient presented again with increased appetite, and he was found with low TSH and high free T4. Within the following 3 months, his free T4 and TSH normalized. At his most recent evaluation, his TSH was normal and the free T4 was borderline-high; the TG antibody titer was still elevated and the TSI titer was negative. To our knowledge, this is the first patient reported with Hashimoto thyroiditis and recurrent hyperthyroidism. This case exemplifies the variability of the manifestations and natural history of Hashimoto thyroiditis and supports the need for a long-term evaluation of patients with autoimmune thyroid disease.