Endocrine Abstracts

Background: Oral levothyroxine (LT4) is usually an effective treatment for hypothyroidism. However, timing of meals, concurrent medications and gastrointestinal diseases causing malabsorption may impair absorption of oral LT4. We present a patient with Hashimoto’s thyroiditis on LT4 replacement through a gastrostomy tube causing the problem of erratic thyroid function test (TFT) results, successfully managed through the use of once-weekly intramuscular LT4 injection.

Clinical case: A 65-year-old Chinese male was on follow-up with our clinic for multi-nodular Hashimoto’s goiter requiring thyroxine replacement, 125ug/d, resulting in serum free thyroxine (fT4) 15 pM (RR 8–21 pM), and thyroid stimulating hormone (TSH) 1.12 mIU/L (RR 0.34–5.6 mIu/L). His co-medications were aspirin, famotidine, lisinopril, atenolol, trimetazidine and simvastatin. He was diagnosed with squamous cell carcinoma of the tongue and lip in 2006, requiring multiple surgeries, radiotherapy and eventually on 24/2/17, permanent gastrostomy tube feeding. However, he experienced multiple episodes of blocked gastrostomy tube due to luminal obstruction by residual feeds requiring urgent tube change. Despite a body weight of 50kg (BMI 19.1 kg/m2), the patient required increasing doses of levothyroxine up to 100mcg daily. Despite the high dose of levothyroxine, he continued to experience fluctuating fT4 levels, ranging from 4 to 13 pM, and TSH levels, ranging from 2.04 to 69.52mIU/L. As he was compliant and administered his doses of medication correctly through the PEG (via crushing of tablets and suspension in plain water), we hypothesized that his labile TFT results were due to poor enteral delivery of LT4 through the gastrostomy tube. Thereby on 16/11/17, the patient was started on intramuscular LT4 400mcg injection once weekly. At the 8^th cycle, serum fT3, fT4 and TSH levels were measured pre-dose (trough), 4 hours post-dose (peak), and on day 1, day 3 and day 6.

His fT3 levels remained stable throughout the entire duration. His trough fT4 of 8 and peak fT4 of 15 were adequate and appropriate. He remained free of symptoms of hyperthyroidism and hypothyroidism and reported no side effects from the intramuscular levothyroxine regime.

Conclusion: This case demonstrates that in hypothyroid patients with impaired enteral delivery of LT4, once-weekly intramuscular injection of LT4 can safely and effectively provide stable serum fT4 and fT3 levels.