Thread: ratoionale of thyroxine

wats rationale of using thyroxine b4 radioisotope 4r thyroid carcinoma

i cud not understand well bhavana. actually we will give thyroxine AFTER radioablation to supress TSH and there by preventing growth promoting action of tsh on thyroid.... actualy this also nt accepted these days as there is no change in recurrence rate vt r vt out thyroxine....

no rupu i m asking , after doing near total r total thyroidectomy radioiodine is used after liothyronine r thyroxine followed by withdrawl. the reason for it?can radioiodine b given without this either for ablation of remaining normal tissue r scanning dose for detectig metestasis

in harrison it is given as" in preparation 4 radioablation of remnant tissue.". any way still i cant understand

• You can treat metastatic disease with radioiodine therapy plus ablation of any residual thyroid tissue
  
  This will prevent reccurrence
• Also, radioiodine therapy can ablate local recurrences that can't be removed surgically
  
  
• After thyroidectomy, postoperative radioiodine therapy can decrease recurrence and death rates
  
  This is in high risk patients
• Long-term use of thyroid hormone therapy has shown beneficial effects on survival and recurrence

........is this what your asking?

Originally Posted by bladder

• You can treat metastatic disease with radioiodine therapy plus ablation of any residual thyroid tissue
  
  This will prevent reccurrence
• Also," radioiodine therapy can ablate local recurrences that can't be removed surgically"
  
  
• After thyroidectomy, postoperative radioiodine therapy can decrease recurrence and death rates
  
  This is in high risk patients
• Long-term use of thyroid hormone therapy has shown beneficial effects on survival and recurrence

........is this what your asking?

ya thats true,but in giving radioiodine as prime modality of treatment thyroxine given for certain duration followed by its withdrawl before radioiodine . y should that b done is my q?

In metastatic ca. thyroid(splly papillary/those cases of follicular that concentrate iodine) after thyroidectomy,high dose radio iodine is used as palliative therapy.Prior stimulation with TSH is recommended in this case..
Source:Tripathi.
Are u sure it's thyroxine and not TSH that u'r asking about?

Originally Posted by bhavana.g

no rupu i m asking , after doing near total r total thyroidectomy radioiodine is used after liothyronine r thyroxine followed by withdrawl. the reason for it?can radioiodine b given without this either for ablation of remaining normal tissue r scanning dose for detectig metestasis

Prior to treatment the Blood TSH must be grossly elevated.

This may be done in two ways:

The traditional method is to stop thyroid medication (T3 or T4) until the TSH is grossly elevated. This takes 3-4 weeks in the case of T4 and 2 weeks in the case of T3.

Without thyroxine one feels very weak and as a result T3 replacement is preferred.

To avoid this problem there is now a method of giving intramuscular recombinant TSH (rhTSH),which allows the patient to continue thyroxine still allowing an effective uptake of radioactive iodine by thyroid tissue.


In ablating, thyroid remnants and if using recombinant human thyroid stimulating hormone is as effective as withdrawal of thyroxine.This trial is known as the HiLo trial.The trial is being funded Cancer Research UK.Physicains in the UK are encouraged to be involved in this trial.



TSH level at the time of radioactive ablation:.


If the TSH is less than 30 Iu/l the the ablation should be delayed or two intramuscular injections of recombinant TSH given.Radiactive iodine with a low TSH is a waste of time and not effective!




Role of Radioactive Iodine Therapy in Cancer of the Thyroid

It is very difficult to remove all the thyroid tissue when performing a "total thyroidectomy". Radioactive iodine is used to destroy any missed normal thyroid tissue in the neck or malignant thyroid tissue that was not removable.Radioactive iodine works because normal thyroid tissue concentrates iodine from the blood stream.In addition under the influence of high TSH levels,malignant thyroid tissue usually takes up iodine in significant amounts.This phenomenon allows the residual thyroid tissue to receive a large targeted dose of radiation with little damage to the surrounding structures.

Radioactive iodine is used in three separate situations:

#1.After Surgery to destroy any residual thyroid cancer cells or residual normal thyroid tissue.

#2.To treat thyroid cancer that has spread to the lymph nodes,lungs or bones.

#3.To treat thyroid cancer that has come back after initial treatment by surgery or previous radioactive iodine or both.



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Risk group-based management of differentiated thyroid carcinoma

A number of controversies exist in the treatment of differentiated thyroid carcinoma with respect to the extent of surgery, use of radioactive iodine and post-operative thyroxine suppression.

Recent recognition of prognostic factors has helped to assign patients, based on their risk profile, as being at high risk of developing recurrence. This has facilitated the development of a selective approach to therapy, thus, avoiding unnecessary treatment and reducing morbidity without compromising treatment outcome. This review attempts to evaluate the current concepts of management of differentiated thyroid carcinoma in the light of these new developments.



Radioiodine treatment

Radioiodine is used in the management of differentiated thyroid carcinoma based on the premise that normal, as well as malignant thyroid tissues, have selective uptake of radioactive iodine. It is used in various situations including screening for distant metastases, ablative treatment of residual normal thyroid tissue and treatment of distant metastases. Whether all patients with differentiated thyroid cancer should be reviewed and treated is controversial. In a recent survey of 233 thyroid experts 61% advised routine postoperative radioiodine treatment.

Two recent retrospective studies have demonstrated that adjuvant radioiodine treatment reduces recurrence in patients with differentiated thyroid cancer. One of these studies also has found a significant advantage for survival in the radioiodine treated group.6 No other studies have confirmed these findings. Several independent investigators have reported no significant advantage of using radioiodine in preventing disease recurrence of differentiated thyroid carcinoma. Also, no obvious correlation has been found with respect to the survival rate of patients with differentiated thyroid carcinomas, even in high-risk cases, treated by adjuvant radioiodine.

One of the major arguments for the routine use of radioiodine is to eliminate possible microscopic multifocal disease. As discussed in the previous section, however, multifocal microscopic disease does not have any prognostic significance in differentiated thyroid carcinomas. The debate of radioiodine treatment and the extent of thyroid surgery are inseparable. If routine adjuvant radioiodine treatment is recommended then all patients should undergo total thyroidectomy, as presence of normal thyroid tissue negates the efficacy of radioiodine treatment.

The controversy of radioiodine treatment can be effectively addressed with the application of prognostic factors and risk group analysis. Based on the available clinical evidence it can be said that patients with low-risk differentiated thyroid cancer can be managed effectively by limited thyroid surgery without adjuvant radioiodine treatment. As the incidence of distant metastases in this group of patients is very low (1 to 7%) they also do not need to undergo surveillance using radioiodine scanning.

The patients with distant metastases clearly need total thyroidectomy and postoperative radioiodine treatment. It is recognised that in about 25% of patients with distant metastases fail to concentrate radioiodine.

The patients with high-risk tumours may also benefit from having a radioiodine scan, ablation (if uptake is >1-2%), and follow-up screening. Treatment of the patients in the intermediate risk group should be individualised based on the risk factor profile.


Thyroxin suppression

Adjuvant thyroxin treatment is given to maintain a low thyroid stimulating hormone level so as to suppress the activity of thyroid tissue through the thyroid-hypothalamus-pituitary negative feedback axis. Cunningham et al (1990) in a multi-variate analysis of differentiated thyroid carcinoma reported its effectiveness in improving survival rate in patients over 50, a finding others have confirmed.

The current literature is in agreement that all patients with differentiated thyroid carcinoma will benefit from thyroxin suppression treatment. A thyroid-stimulating hormone level which is below normal but easily detectable has been shown to be equally effective as a nondetectable thyroid stimulating hormone level. Despite concurrence about the detrimental effect of thyroxine suppressive therapy on bone density, Marcocci et al (1994) demonstrated that carefully monitored suppressive therapy is not associated with bone loss in pre-menopausal women.



I hope , this may c l a r i f y your Query.