Hypothalamic-pituitary-thyroid axis in acromegaly

Thyroid autoimmune disorders in patients with acromegaly

PURPOSE

Disorders of the hypothalamic-pituitary-thyroid axis are common in patients with acromegaly and thyroid enlargement is present in the majority of them. The exact prevalence of goiter in patients with acromegaly remains uncertain and the presence of thyroid autoimmunity has not been extensively evaluated so far.

METHODS

We retrospectively evaluated thyroid biochemical and morphological findings in 116 acromegalic patients who attended our hospital. Serum TSH, total thyroxine levels and anti-thyroid peroxidase (ATPO) antibodies were measured by standard ultrasensitive techniques in all the patients. Thyroid ultrasound was performed in 75 out of them. The antibody control group was composed by healthy Argentinean individuals who attended the blood bank of our hospital in whom ATPO antibodies were measured.

RESULTS

Twenty-nine out of the 116 acromegalic patients (25 %) showed elevated titers of thyroid antibodies (79 % were women and 21 % men). The control group had a 10 % prevalence of thyroid autoimmunity. The prevalence of goiter by ultrasound was 36 %, being more common in females (41 %) than in males (28 %). Thirty-five percent of patients who presented thyroid nodules and 44 % of patients with ultrasound diagnosed goiters had positive thyroid autoimmunity. There was no significant correlation between the presence of nodules and IGF-1 levels, duration of disease or age.

CONCLUSION

We found a high prevalence of thyroid autoimmunity in our patients with acromegaly as compared to the normal population. Thyroid autoimmunity seems to be an additional mechanism for the development of thyroid disorders in acromegaly.

Thyroid volume and function in patients with acromegaly living in iodine deficient areas

The aim of our study was to evaluate the size and function of the thyroid in patients with acromegaly. In 39 patients concentrations of HGH, PRL, TSH, T3 and T4 were measured and the thyroid volume was calculated with the using of ultrasound examination. The control group comprised 5 patients with acromegaly in a stage of remission and 98 controls. We concluded that the size of the goiter in patients with acromegaly depends on serum concentration of HGH, but it does not depend on the concentration of TSH, T3, T4 and PRL. Goiter is present in 87% of patients with acromegaly, 46% of them are nodular goiters. The thyroid function in acromegaly is normal.

The influence of diabetes mellitus on thyrotropin response to thyrotropin-releasing hormone in untreated acromegalic patients

Impairment of thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) has been documented in patients with uncontrolled diabetes mellitus (DM). In acromegalic patients, however, there have been no data regarding TSH secretion studied taking the existence of DM into consideration. Therefore, we investigated the TSH response to TRH [expressed as TSH increment (delta TSH)] in 14 untreated acromegalic patients, who did not show the suprasellar extension of adenoma, divided into two groups on the basis of either presence or absence of uncontrolled DM, and in 28 normal subjects. The mean max delta TSH was significantly reduced (p less than 0.02) in acromegalic patients despite similar mean serum T4 and free T4 index (FT4l) levels. Furthermore, the mean basal and max delta TSH in 7 patients with DM (FBS, 120-300 mg/dl; HbA1, 8.8-15.2%) were significantly lower than those in 7 patients without DM (p less than 0.05 and p less than 0.02, respectively) despite similar the mean serum T3, T4, FT4l, growth hormone (GH) and prolactin (PRL) levels and sellar volume. In 4 patients with DM the TSH response to TRH 6-8 weeks after insulin therapy, when their HbA1 levels were normal, increased compared to that before insulin therapy. The mean max delta TSH after selective adenomectomy in 8 patients (3 in DM group and 5 in non-DM group), whose fasting basal GH fell to less than 5 ng/ml, was almost identical to that in normal subjects. In conclusion, the present study suggests that the abnormality in TSH secretion in acromegalic patients may be increased by the existence of uncontrolled DM.