Diabetes mellitus, similar to other nonthyroidal illnesses, is associated with circadian rhythm abnormalities of serum TSH and thyroid hormones.
In this study, we investigated the effect of good and poor metabolic control on the nocturnal serum TSH peak and the TSH response to TRH stimulation in diabetic patients.32 diabetic patients (type 1, n=9; type 2, n=23; 18 men, 14 women; the mean age: 45.8 (10.5 yrs) with either poor glycemic control (n=22) or good glycemic control (n=10) were enrolled in this study. The nocturnal serum TSH peak (22 30-0200h) was abolished in the poor glycemic control group, whereas there was a statistically significant peak in the other group (p=0.0001). The morning serum TSH value in the diabetics with the poor glycemic control group did not differ from that in the other group, but the serum TSH and TT4 were significantly higher in the good glycemic control group than the other group and no differences were found in the increase of serum FT4, TT3 and FT3 levels between the two groups after TRH stimulation. The morning serum TT4 and TT3 levels were significantly higher in the good glycemic control group than the other group (p=0.04, p=0.007) whereas the morning serum FT4, FT3 and TSH values did not differ in the two groups. The increase in the serum TSH and TT4 levels after TRH stimulation were significantly higher in the good glycemic control group than the other control group whereas there were no difference in the increase in the serum TT3, FT4 and FT3 levels between the two groups.
In conclusion, metabolic control affects the hypothalamus-pituitary-thyroid axis and the metabolic decompensation in diabetic patients leads to the impairment of TSH secretion, thyroid hormones secretion and their response to TRH.
Keywords: TSH, thyroid hormones, glycemic control