Hypothyroidism following 131I therapy for hyperthyroidism in relation to immunologic parameters

The Incidence of Hypothyroidism Following the Radioactive Iodine Treatment of Graves' Disease and the Predictive Factors Influencing its Development

The purpose of this study is to evaluate and compare the incidence of hypothyroidism following different fixed radioactive iodine-131 (¹³¹I) activities in the treatment of Graves’ disease (GD) and to investigate the predictive factors that may influence its occurrence. This retrospective analysis was performed on 272 patients with GD who were treated with ¹³¹I, among whom 125 received 370 MBq and 147 received 555 MBq. The outcome was categorized as hypothyroidism, euthyroidism, and persistent hyperthyroidism. Multiple logistic regression analysis was performed to identify significant risk factors that affect the development of hypothyroidism. The incidence of hypothyroidism following the first low activity was 24.8% with a high treatment failure rate of 58.4%, compared with 48.3% and 32% following high activity. The overall cumulative incidence of hypothyroidism following repeated activities was 50.7%, out of which 73.9% occurred after the first activity and 20.3% after the second activity. The higher ¹³¹I activity (P < 0.001) and average and mild enlargement of the thyroid gland (P = 0.004) were identified as significant independent factors that increase the rate of incidence of hypothyroidism (Odds ratios were 2.95 and 2.59). No correlation was found between the development of hypothyroidism and the factors such as age, gender, presence of exophthalmos, previous antithyroid medications, and the durations, and Technetium-99m (Tc-99m) pertechnetate thyroid uptake. In view of the high treatment failure rate after first low activity and lower post high activity hypothyroid incidence, high activity is recommended for GD patients, reserving the use of 370MBq for patients with average sized and mildly enlarged goiter; this increases patient convenience by avoiding multiple activities to achieve cure and long-term follow-up.

[Short-term results of treatment with 131I in patients with multinodular goiter: effect of the associated degree of hyperthyroidism and other variables]

OBJECTIVE

To assess the effectiveness of radioactive iodine (RAI) therapy and the incidence of hypothyroidism post RAI in patients with subclinical hyperthyroidism or clinical hyperthyroidism with Multinodular Goiter (MNG).

METHODS

A retrospective study of 69 consecutive patients treated with (131)I for MNG during the year 2008 observed for six months. All patients received a single fixed dose of 16 mCi (592 MBq) weighted by the gland size. They were categorized into two groups: subclinical hyperthyroidism or clinical hyperthyroidism. We compared the success rate and the incidence of hypothyroidism.

RESULTS

The thyroid dysfunction was corrected in 82.09% of the patients. Success rate was 100% in the clinical hyperthyroidism group and 78.13% in the subclinical hyperthyroidism group (P=0.105). The overall incidence of hypothyroidism was 16.42%; 25.00% of patients with clinical hyperthyroidism and 14.55% with subclinical hyperthyroidism developed this secondary effect (P=0.400). No statistically significant differences were found in the success rate in the incidence of hypothyroidism when the results were analyzed according to the thyrotropin decrease in patients with subclinical hyperthyroidism. Seven patients had positive anti-thyroid peroxidase antibodies (anti-TPO) before therapy. The incidence of hypothyroidism was significantly higher in them (57.14% vs 11.67%; P=0.011). Cardiac arrhythmias were four times more frequent in patients with clinical hyperthyroidism. Previous treatment with thiamazol positively affected the outcome.

CONCLUSIONS

A single fixed weighted dose of (131)I is highly effective and safe for the control of clinical and subclinical hyperthyroidism due to MNG. Patients with anti-TPO antibodies may have a high risk of developing post-iodine hypothyroidism.

[Short-term results of treatment with 131I in patients with multinodular goiter: effect of the associated degree of hyperthyroidism and other variables]

OBJECTIVE

To assess the effectiveness of radioactive iodine (RAI) therapy and the incidence of hypothyroidism post RAI in patients with subclinical hyperthyroidism or clinical hyperthyroidism with Multinodular Goiter (MNG).

METHODS

A retrospective study of 69 consecutive patients treated with (131)I for MNG during the year 2008 observed for six months. All patients received a single fixed dose of 16 mCi (592 MBq) weighted by the gland size. They were categorized into two groups: subclinical hyperthyroidism or clinical hyperthyroidism. We compared the success rate and the incidence of hypothyroidism.

RESULTS

The thyroid dysfunction was corrected in 82.09% of the patients. Success rate was 100% in the clinical hyperthyroidism group and 78.13% in the subclinical hyperthyroidism group (P=0.105). The overall incidence of hypothyroidism was 16.42%; 25.00% of patients with clinical hyperthyroidism and 14.55% with subclinical hyperthyroidism developed this secondary effect (P=0.400). No statistically significant differences were found in the success rate in the incidence of hypothyroidism when the results were analyzed according to the thyrotropin decrease in patients with subclinical hyperthyroidism. Seven patients had positive anti-thyroid peroxidase antibodies (anti-TPO) before therapy. The incidence of hypothyroidism was significantly higher in them (57.14% vs 11.67%; P=0.011). Cardiac arrhythmias were four times more frequent in patients with clinical hyperthyroidism. Previous treatment with thiamazol positively affected the outcome.

CONCLUSIONS

A single fixed weighted dose of (131)I is highly effective and safe for the control of clinical and subclinical hyperthyroidism due to MNG. Patients with anti-TPO antibodies may have a high risk of developing post-iodine hypothyroidism.

Thyroid Disease Associated With Exposure to the Nevada Nuclear Weapons Test Site Radiation

BACKGROUND

A study was begun in 1965 to 1966 to determine whether children exposed to radioactive iodine from nuclear weapons testing at the Nevada Test Site from 1951 through 1962 were at higher risk of thyroid disease. In 1993, we reported that among those examined in 1985 to 1986 (Phase II) there was an association between radiation from the Nevada Test Site and thyroid neoplasms.

METHODS

We reevaluated the relationship between exposure to Nevada Test Site fallout and thyroid disease using newly corrected dose estimates and disease outcomes from the Phase II study. A prospective cohort of school children 12 to 18 years old living in Utah, Nevada, and Arizona was first examined for thyroid disease in 1965 to 1966 and reexamined in 1985 to 1986. In the Phase II report, 2497 subjects formed the basis for this analysis. Thyroid disease, including thyroid neoplasms and thyroiditis, was expressed as cumulative incidence and risk ratios (RRs) with a dose-response expressed as excess risk ratio (ERR/Gy).

RESULTS

The RR between thyroid radiation dose in the highest dose group and thyroid neoplasms increased from 3.4 (in the earlier analysis) to 7.5. The RR for thyroiditis increased from 1.1 to 2.7 with an ERR/Gy of 4.9 (95% confidence interval = 2.0 to 10.0). There were too few malignant thyroid neoplasms to estimate risk.

CONCLUSIONS

Persons exposed to radioactive iodine as children have an increased risk of thyroid neoplasms and autoimmune thyroiditis up to 30 years after exposure.

Three basic patterns of changes in serum thyroid hormone levels in Graves' disease during the one-year period after radioiodine therapy

The purpose of this study was to clarify the characteristic patterns of the thyroid hormonal changes in Graves' disease during the one-year period after 131I therapy considering that few serial hormonal data during this period are available in the literature.

METHODS

The levels of serum T3, T4 and FT4 before and during one year were plotted as a function of time in 70 therapy courses of 58 patients without subsequent antithyroid or steroid therapy.

RESULTS

35 euthyroid, 6 hypothyroid and 29 hyperthyroid states were obtained during one year after therapy. Although individual patients had individual hormonal changing patterns, 3 common basic patterns were observed from baseline to one month (early) and thereafter (late), respectively. The early patterns were a decrease in 54 (77%), a minimum change in 8 (11.5%) and an increase in 8 (11.5%). The late patterns were a stable state after an initial decrease with a bottom followed by an increase (valley pattern) in 47 (67%), a stable state after an initial increase with a peak followed by a decrease with a bottom and a subsequent re-increase (mountain pattern) in 12 (17%) and a late stable state after a gradual slow decrease without an obvious bottom near or till one year (downhill pattern) in 11 (16%). The bottom level and the degree of hormonal recovery from the bottom determined the stable euthyroid, hypothyroid or hyperthyroid state in 49 (86%) of 57 with the valley or mountain pattern. Most of the bottom levels (81%) and transient abnormal changes including transient hypothyroidism (93%, 13/14), peak or hyperthyroidism (85%, 11/13) and euthyroidism (67%, 10/15) appeared within 6 months. The post-therapeutic stable euthyroid, hypothyroid or hyperthyroid state could be judged from the hormonal patterns in 57% (39/68) from 2.5 to 6 months, in 18% (12/68) from 6 to 9 months and in 25% (17/68) thereafter.

CONCLUSION

Although the changes in thyroid hormones are not constant in Graves' disease during one year after 131I therapy, there are three basic patterns; valley, mountain and downhill patterns from one month after therapy. The post-therapeutic stable state can be judged by the hormonal level recovered from the bottom in most patients.

Long-term incidence of hypothyroidism after radiotherapy in patients with head-and-neck cancer

PURPOSE

To determine the long-term incidence of postirradiation hypothyroidism (HT) in patients with head-and-neck cancer.

METHODS AND MATERIALS

The incidence of overt HT was assessed prospectively in 391 patients with nonthyroid head-and-neck cancer admitted for radiotherapy (RT) consecutively between 1990 and 1996. Eighty-three patients were excluded from the analysis because of known thyroid disease before treatment (n = 27), no RT was given (n = 15), or inadequate follow-up (n = 41). Overt HT was defined as increased thyroid-stimulating hormone (TSH) in combination with decreased fT4/T4 or in combination with initiation of thyroxine replacement therapy.

RESULTS

With a median follow-up of 4.2 years (range, 3 months to 10.9 years) for 308 evaluable patients, the 5- and 10-year Kaplan-Meier actuarial risks of HT were 20% and 27%, respectively. The median time until development of HT was 1.8 years (3 months to 8.1 years). Multivariate analysis showed that patients with bilateral RT to the neck had a higher risk of HT in comparison with unilateral neck RT (relative hazard, 0.37; p = 0.02). The addition of surgery to RT increased the overall risk of HT (p < 0.001); and if surgery involved the thyroid gland, the relative hazard was 4.74 (p < 0.001). For an elevated pre-RT TSH value, the relative hazard was 1.58 (p < 0.001).

CONCLUSION

The incidence of overt HT after locoregional RT for nonthyroid head-and-neck cancer continues to increase with time, even after long-term follow-up. We recommend life-long TSH testing in these patients.

Characterization of thyroid-stimulating blocking antibodies that appeared during transient hypothyroidism after radioactive iodine therapy

Hypothyroidism after radioactive iodine (RAI) therapy for Graves' disease can be transient or permanent. The cause for early transient hypothyroidism is unknown. We evaluated 11 patients who developed transient hypothyroidism within 6 months of RAI and 12 who remained euthyroid after RAI. Approximately equal numbers of patients in each group had thyroid-stimulating antibody (TSAb) that increased cyclic adenosine monophosphate (cAMP) levels in Chinese hamster ovary (CHO) cells transfected with the recombinant human thyrotropin receptor (TSHR) (WT cells). Approximately equal numbers of patients from both groups had an increase in TSAb activity post-RAI. All TSAbs had their dominant functional epitope on the N-terminus of the TSHR extracellular domain, requiring residues 90-165 for activity because they, but not TSH, completely lost stimulating activity in a receptor chimera, wherein TSHR residues 90-165 were substituted by equivalent residues of the lutropin/choriogonadotropin receptor (LH/CGR). Although equal numbers of patients in both groups had thyrotropin-binding inhibiting immunoglobulin activity (TBII), as measured by radioreceptor assay before RAI, patients with transient hypothyroidism had a surge in TBII activity and all except one became positive for thyroid-stimulating blocking antibodies (TSBAb), as measured by inhibition of TSH-stimulated cAMP from WT cells. When immunoglobulin G (IgGs) were epitope-mapped using TSHR/LH-CGR chimeras with different substitutions, 8 hypothyroid subjects had TSBAbs directed against residues 90-165 of the TSHR, as well as TSHR residues 261-370. Two had functional epitopes directed at residues 9-89 as well as TSHR residues 261-370. None of the euthyroid control patients developed TSBAbs and their TBII activity decreased post-RAI. When patients with transient hypothyroidism reverted to a euthyroid state, TSAb was still detectable in 5; however, TBII was present in all and TSBAb, although decreased, was still positive in 9. In summary, RAI therapy was associated with a change in thyroid antibody characteristics in most patients. Additionally, patients with a surge in TBII and the appearance of TSBAb developed transient hypothyroidism after RAI.

Specific effects of radioiodine treatment on TSAb and TBAb levels in patients with Graves' disease

Radioactive iodine (RAI)-induced changes in the levels of antibodies to the thyroid-stimulating hormone (TSH) receptor (TRAb) in patients undergoing treatment for autoimmune thyroid disease have been well documented. Previous studies have reported effects on the overall level of the antibodies present, TSH-binding inhibitory immunoglobulins (TBII), without detailed studies of specific effects on the levels of thyroid-stimulating (TSAb) or thyroid-blocking antibodies (TBAb). More detailed studies have been reported only in individual cases. In this study, the values of TSAb, TBAb, and TBII were measured longitudinally in 33 patients (27 females and 6 males) who received RAI. The bioassays for TSAb and TBAb were performed in JPO9 cells. Following RAI, there were significant and immediate effects on the values of TBII in 70% of patients. TBII levels fell in 7 patients (20%) (Group 1), rose in 16 patients (48%) (Group 2) or remained unchanged but elevated in 10 patients (32%) (Group 3). In the Group 1 patients, only TSAb were detectable and none of these patients became hypothyroid after treatment. In the 16 patients in Group 2, increases in TBII were attributable to specific increases in TSAb in 7 (44%), in TBAb in 3 (19%), and in both TSAb and TBAb in 3 (19%). There were 3 patients (19%) in this group in whom there was no detectable TSAb or TBAb activity despite the increase in TBII. Six patients from this group became hypothyroid within 6 months of RAI treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

A reappraisal of the role of methimazole and other factors on the efficacy and outcome of radioiodine therapy of Graves' hyperthyroidism

The outcome of radioiodine therapy of Graves' hyperthyroidism was retrospectively evaluated in 274 consecutive patients treated from 1975 to 1984. At 1-yr follow-up, permanent hypothyroidism occurred in 36.9% of patients and the cumulative incidence of hypothyroidism progressively increased up to 79.3% after 7-10 yr. At the end of the follow-up period, 148 patients (54%) were hypothyroid, 115 (42%) euthyroid and 11 (4%) still hyperthyroid. The prevalence of hypothyroidism was significantly higher in patients with small goiters (less than or equal to 50 g) than in those with large goiters (greater than 90 g). Moreover, hypothyroidism was more frequent in patients with high thyroglobulin antibodies titers (greater than or equal to 1:25,600) than in those with low titers or negative tests, and occurred earlier in the former group than in the latter ones Correction of thyrotoxicosis was obtained after the administration of a single dose of 131I in 187 patients (63.6%); 69 patients required two doses and 11 three or more doses. Seven patients refused further treatment with 131I after the first dose. In an effort to identify possible factors affecting the efficacy of 131I therapy, we evaluated the results obtained after the administration of the first dose of radioiodine. We found that large goiters, rapid iodide turnover and adjunctive therapy with methimazole shortly after radioiodine were associated with a higher rate of persistence of thyrotoxicosis, whereas an increased prevalence of hypothyroidism was observed in patients with small goiters and in those not treated with methimazole up to one week after 131I.(ABSTRACT TRUNCATED AT 250 WORDS)

Current treatment of Graves' disease

In this review we have described the rationale for the appropriate treatment of patients with Graves' disease. Because the etiology of this disorder remains obscure, its management remains controversial. Since antithyroid drugs and radioiodine became readily available in the early 1950s, they have been widely used for the treatment of thyrotoxicosis, and the number of cases treated surgically has markedly decreased. However, almost four decades of experience have disclosed an unexpectedly high incidence of delayed hypothyroidism after radioiodine treatment and a low remission rate after antithyroid therapy. As a result, surgery is again being advocated as the treatment of choice. The three modalities of treatment have different advantages and disadvantages, and selection of treatment is of importance. In principle, we believe that for most patients a subtotal thyroidectomy should be performed after the patient has been rendered euthyroid by antithyroid drugs. We attempt to leave a thyroid remnant of 6 to 8 gm.

Low-dose 131I in treatment of Graves' disease

One hundred and sixty-four patients with Graves' disease were treated with low-dose radioiodine (2 mCi), with a mean follow up of 4 1/2 years. At this time 74 (45%) were euthyroid having had a single dose, with a total of 131 (80%) being controlled with one or more doses. Three (2%) were still toxic but their mean follow up was only 3 years. Thirty (18%) were rendered hypothyroid, two-thirds of these after a single dose of 2 mCi 131I. The one-year incidence of hypothyroidism was 6%, with an incidence at 6 years of 20%. Previous surgery, medical treatment and thyroid antibody status appeared to have no influence on the outcome.

Long-term follow-up study of compensated low-dose 131I therapy for Graves' disease

We treated 187 patients who had Graves' disease with low-dose radioactive iodide (131I), using a protocol that included a compensation for thyroid size. The incidence of early hypothyroidism (12 per cent) was acceptably low in the first year after 131I treatment, but we found a cumulative high incidence (up to 76 per cent) at the end of the 11th year. In contrast, the incidence of permanent hypothyroidism was relatively stable in 166 surgically treated patients, increasing from 19 to 27 per cent at the end of 11 years. Among 122 medically treated patients, only 40 per cent entered remission, and hypothyroidism developed in 2 per cent during the same period of follow-up. The long-term incidence of hypothyroidism in our patients treated with low-dose 131I therapy was much higher than that found in earlier studies using a comparable dose. Our study suggests that it will be difficult to modify therapy with 131I alone to produce both early control of thyrotoxicosis and a low incidence of hypothyroidism.

Incidence of hypothyroidism after 131I therapy for hyperthyroidism. Relation to pretherapy serum levels of T3, T4 and thyroid antibodies

A correlation is reported between serum levels of triiodothyronine (S-T3) and thyroxine (S-T4) before treatment, as well as levels of thyroid antibodies before treatment, and the development of hypothyroidism following 131I therapy in 86 patients with hyperthyroidism. Patients with marked elevation of S-T3 or S-T4 had demonstrable antibodies to thyroid cytoplasmic antigen more often than those with normal or moderately elevated levels, and patients with markedly elevated levels of S-T3 also had a higher incidence of hypothyroidism after treatment. Patients with nodular thyroid glands and with markedly elevated levels of S-T3 required a larger number of 131I doses before no signs of hyperthyroidism persisted in comparison to those with moderately elevated levels.