Successful treatment of hyperthyroidism due to nonneoplastic pituitary TSH hypersecretion with 3,5,3'-triiodothyroacetic acid (TRIAC)

Effects of thyroid hormones (T4,T3), bromocriptine and Triac on inappropriate TSH hypersecretion

Inappropriate TSH hypersecretion was diagnosed in a 38-year-old woman (case 1) and in a 38-year-old man (case 2). Both of them had earlier been treated by ablative therapy for hyperthyroidism. The present diagnosis was based on elevated basal serum TSH levels despite elevated serum free thyroid hormone levels. Both of them had exaggerated TSH responses to TRH (peak value 240 mU/l in case 1 and 408 mU/l in case 2). Their albumin and prealbumin levels were normal. The serum TBG level was normal in case 1 but was elevated in case 2. Serum levels of alpha-subunits of TSH, and pituitary CT scans were normal. Despite mild clinical hyperthyroidism, peripheral indices of thyroid hormone action were normal. They had also relatives with apparent resistance to thyroid hormones. In view of the possibility that prolonged pituitary thyrotrophic stimulation is detrimental, various therapeutic approaches to suppress TSH levels were tried. Both T3 and T4 treatments lowered serum TSH levels, but were poorly tolerated. Acute administration of L-dopa or bromocriptine reduced serum TSH levels, but this was not seen during long-term therapy. TRIAC treatment lowered serum TSH levels, and the drug was well tolerated. Serum TSH responses to TRH were not blunted during T3, T4 or TRIAC treatments. Somatostatin also reduced serum TSH levels, but did not potentiate the effect of low dose T3 therapy. Our results suggest that the patients had unbalanced pituitary and peripheral thyroid hormone resistance, predominantly at the pituitary level. Of the drugs studied, TRIAC seemed to be the most suitable therapy.

3,5,3'-Triiodothyroacetic acid minimizes the pituitary thyrotrophin secretion in patients on levo-thyroxine therapy after ablative therapy for differentiated thyroid carcinoma

The aim of this study was to examine the influence of 3,5,3'-triiodothyroacetic acid (TRIAC) on serum thyrotrophin (TSH) concentration in 25 patients on levo-thyroxine (L-T4) therapy after ablative therapy for differentiated thyroid carcinoma. The daily L-T4 intake amounted to 2.6 +/- 0.7 micrograms/kg body weight (+/- SD). Serum TSH concentration was determined by means of a sensitive radioimmunometric method (lower detection limit 0.03 mU/l). The median (means) basal TSH concentration under L-T4 amounted to 0.11 mU/l (range less than 0.03 mU/l-7.39 mU/l). During supplementary intake of 500 micrograms TRIAC daily the median basal TSH decreased to 0.04 mU/l range less than 0.03 mU/l-0.24 mU/l; P less than 0.0003). The TRIAC-induced decrease in 17 out of 20 basal TSH-concentrations exceeding 0.03 mU/l ranged from 38% to as much as 98%. TRIAC reduced the median TRH-stimulated TSH concentration from 0.25 mU/l (range less than 0.03 mU/l-47.3 mU/l) to 0.04 mU/l (range less than 0.03 mU/l-1.43 mU/l; P less than 0.0001). A blunted TSH-response to TRH occurred in 8.7% prior to and in 52% of the patients during TRIAC medication. Side effects such as nervousness, cardiac arrhythmia or tachycardia under supplementary TRIAC (500 micrograms daily) were observed in four patients. The conclusion is that the supplementary medication of 500 micrograms TRIAC daily in euthyroid patients on L-T4 medication after thyroid gland ablation for differentiated thyroid cancer is an effective means to minimize serum-TSH concentration.

Dissociated thyromimetic effects of 3, 5, 3'-triiodothyroacetic acid (TRIAC) at the pituitary and peripheral tissue levels

Although TRIAC is bound at least twice as avidly to nuclear receptor as T3, its thyromimetic potency is relatively low and its effect at the pituitary level on thyrotropin (TSH) secretion seems to be dissociated from that at the peripheral tissue level. In order to gain further insight into the complex effects of this thyroid hormone analog, we studied the effects of long-term TRIAC administration (2.8 mg/day for 2 months) on TSH secretion, circulating free thyroid hormone (FT4 and FT3) levels and some parameters able to evaluate the peripheral thyroid hormone action, in 5 mild obese subjects on low caloric diet (1200 kcal/day). The results were compared to those obtained in 5 mild obese subjects matched for age, sex and weight on low caloric diet alone. TRIAC administration completely inhibited the secretion of both basal and TRH-stimulated TSH in few days, and consequently serum FT4 and FT3 concentrations progressively dropped to very low levels, while no significant changes in both TSH and free thyroid hormone levels were recorded in the control group. The body weight significantly fell in both groups, without any difference between TRIAC treated and untreated patients. The heart rate was constant throughout the course of the study in both groups of patients. Serum total cholesterol, triglyceride and total lipid concentrations significantly decreased in both groups, and the decrement recorded in TRIAC treated patients was not significantly different from that found in patients on diet alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-adenomatous inappropriate TSH hypersecretion and euthyroidism requires no treatment

The syndrome of inappropriate TSH secretion is described in a euthyroid girl and her father. Based on nuclear T3 binding studies in fibroblasts, generalized tissue resistance was associated with a lower binding affinity for T3 in nuclear extracts suggestive of a structurally abnormal receptor for T3. Early recognition of the syndrome and observation of the short-term response to thyroid medication prevented unnecessary trials of antithyroid medication and later radical ablative thyroid treatment.

Response of thyrotropin-secreting pituitary adenomas to a long-acting somatostatin analogue

Thyrotropin-secreting pituitary adenomas are aggressive, invasive tumors that respond poorly to available surgical and medical treatments. Inappropriate release of thyrotropin by these tumors can result in hyperthyroidism. We treated five patients who had thyrotropin-secreting pituitary adenomas with the long-acting somatostatin analogue SMS 201-995, which was administered by subcutaneous injection in doses of 50 to 100 micrograms every 8 to 12 hours. Serum levels of thyrotropin were dramatically reduced by treatment in four of the five patients, and levels of another tumor marker, the alpha-subunit of thyrotropin, were reduced in all five. In two patients with hyperthyroidism due to production of excess thyrotropin by the tumor, treatment with the somatostatin analogue resulted in a sustained euthyroid state. One patient who was treated for more than 16 months had a persistent reduction in serum levels of thyrotropin and iodothyronines. We conclude that SMS 201-995 is an effective means of controlling hypersecretion of thyrotropin and the associated hyperthyroidism due to thyrotropin-secreting pituitary tumors.

Abnormal daily periodicity of serum thyrotropin (TSH) and evidence for defective TSH suppression in a case of non-neoplastic syndrome of inappropriate TSH secretion

A non-neoplastic syndrome of inappropriate secretion of TSH (ITSHS) was diagnosed in a hemithyroidectomized and clinically euthyroid 44-yr-old man, who also exhibited limping (Perthes' disease), genu valgum, pes supinatus and lateral nystagmus. Computed tomography demonstrated an enlarged sella turcica due to empty sella. Baseline serum T3, T4, free T3, free T4 and TSH fluctuated between 179 and 274 ng/dl, 6.0 and 13.2 micrograms/dl, 4.2 and 6.0 pg/ml, 7.6 and 15.3 pg/ml, and 4.3 and 33.0 microU/ml, respectively. Serum alpha-TSH subunit was repeatedly normal (0.36-0.69 ng/ml) over the follow-up period (greater than 3 yr). No changes in serum liver enzymes and lipids were observed after thyroid hormone administration, whereas red blood cell glucose-6-phosphate dehydrogenase (G-6-PD) and urinary OH-proline were slightly enhanced during 120 micrograms/day L-T3 regimen. This also resulted in an inappropriately normal glucagon-stimulated cAMP levels. Tachycardia was experienced only during L-T3 and very high L-T4 dose treatments. Therefore, the patient showed some evidence for thyroid hormone peripheral refractoriness. Patient's TSH was physiologically responsive to agents (thyrotropin releasing hormone, methimazole, the dopamine antagonists domperidone and sulpiride) known to elicit its release into circulation, while it responded paradoxically to those which normally inhibit TSH secretion. In fact, the infusion of somatostatin (320 micrograms/h) or dopamine (4 micrograms/Kg/min), and the oral administration of bromocriptine or nomifensine (two dopamine agonists) or corticosteroids (dexamethasone) provoked an unexpected elevation of both unstimulated and TRH-stimulated TSH levels.(ABSTRACT TRUNCATED AT 250 WORDS)