Thyroxine replacement dose in patients with Hashimoto disease: A potential role for interleukin-6

Objective: To investigate the potential association between serum inflammatory cytokine levels and thyroxine replacement dose in patients with Hashimoto disease. Patients and methods: The study included 40 patients (12 men) with a mean age of 56.52 ± 6.12 years who had hypothyroidism due to Hashimoto disease. Serum interleukin-1b (IL-1b), tumour necrosis factor α (TNF-α) and interleukin-6 (IL-6) levels, as well as TSH, T3 and T4 were measured (ELISA). Results: Serum IL-6 showed a significant positive correlation both with total thyroxine replacement dose (r = 0.551, p = 0.001) and with dose per kilogram of body weight (r = 0.482, p = 0.002). There was also a significant negative linear correlation between serum IL6 and T3 (r = −0.322, p = 0.043), as well as between serum IL6 and T3/T4 ratio (r = −0.332, p = 0.036). A further significant (r = 0.419, p = 0.007) positive association was demonstrated between IL6 and TNF-α. However, no association was found between T3 or T3/T4 ratio and TNF-α or IL1b. Conclusions: In patients with Hashimoto disease serum IL-6 levels are positively associated with thyroxine replacement dose and negatively associated with T3 and T3/T4 ratio. These results are possibly attributable to the inhibitory effect of IL6 on deiodination of T3 and imply a role for IL6 in determining thyroxine replacement dose among these patients.