Is Parenteral Levothyroxine Therapy Safe in Intractable Hypothyroidism?

Case: A 32-year old woman was admitted to the hospital due to intractable hypothyroidism refractory to high dose of oral l-thyroxine therapy. She underwent total thyroidectomy and radioactive iodine therapy due to papillary thyroid cancer. After excluding poor adherence to therapy and malabsorption, levothyroxine absorption test was performed. No response was detected. Transient neurologic symptoms developed during the test. She developed 3 attacks consisting of neurologic symptoms during high dose administration. The patient was considered a case of isolated l-thyroxine malabsorption. She became euthyroid after intramuscular twice weekly l-thyroxine therapy.

Discussion: There are a few case reports regarding isolated l-thyroxine. We report successful long term results of twice weekly administered intramuscular l-thyroxine therapy. We also draw attention to neurologic side effects of high dose l-thyroxine therapy.