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 alpha (TNF-alpha) and interleukin-6 (IL-6) levels, as well as TSH, T(3) and T(4) 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 T(3) (r=-0.322, p=0.043), as well as between serum IL6 and T(3)/T(4) ratio (r=-0.332, p=0.036). A further significant (r=0.419, p=0.007) positive association was demonstrated between IL6 and TNF-alpha. However, no association was found between T(3) or T(3)/T(4) ratio and TNF-alpha or IL1b. CONCLUSIONS: In patients with Hashimoto disease serum IL-6 levels are positively associated with thyroxine replacement dose and negatively associated with T(3) and T(3)/T(4) ratio. These results are possibly attributable to the inhibitory effect of IL6 on deiodination of T(3) and imply a role for IL6 in determining thyroxine replacement dose among these patients.