G. F. Fenzi

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 (≤ 50 g) than in those with large goiters (> 90 g). Moreover, hypothyroidism was more frequent in patients with high thyroglobulin antibodies titers (≥ 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 avaluated 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. On the other hand pretreatment with methimazole before radioiodine administration did not affect the outcome of treatment. Thus, if correction of thyrotoxicosis, irrespective of the occurrence of hypothyroidism, has to represent the goal of radioiodine therapy of Graves’ disease, the following points should be kept in mind: i) Large goiters and goiters with a rapid iodine turnover should receive larger 131I doses/g thyroid tissue; ii) Methimazole should not be given shortly after radioiodine: if thyrotoxicosis is severe, the antithyroid drugs may be given prior to 131I therapy to restore euthyroidism, without limiting the efficacy of radiodiodine.

Graves’ IgG stimulation of continuously cultured rat thyroid cells: a sensitive and potentially useful clinical assay

A continuously cultured line of normal rat thyroid (FRTL) cells can be stimulated by immunoglobulin preparations from patients with Graves’ disease as measured by increases in intracellular cAMP levels. Responsiveness is concentration-dependent but is delayed in time relative to thyrotropin. Additionally, the cells respond to Graves’ immunoglobulins which have no long-acting thyroid stimulator (LATS) activity and are negative when adenylate cyclase stimulation in human thyroid membrane preparations is assayed. No correlation exists between the stimulation activity and the ability of a Graves’ immunoglobulin preparation to inhibit thyrotropin binding; cells are responsive even in the presence of such inhibitor activity.

Neuropsychological assessment in schoolchildren from an area of moderate iodine deficiency

Neuropsychological assessment was carried out in schoolchildren from a montane area of Eastern Tuscany (Tiberina Valley). This area was found to be moderately iodine deficient (mean urinary iodine excretion: 39 ώg/g creatinine), with a cumulative goiter prevalence of 51.9% in schoolchildren aged 6-14 yr (goiter prevalence in the control iodine-sufficient area: 5.6%). No significant differences in serum TT4, TT3, FT4I, TSH levels between the endemic and control areas were found, whereas serum thyroglobulin values were significantly higher in the iodine-deficient area (61±8 vs 17±1 ng/ml, p < 0.01). No differences were found as to the height, body weight and pubertal development in the two areas. Neuropsychological assessment, performed in a representative sample of 50 schoolchildren from the endemic area and 50 schoolchildren from the control area, matched for age, sex and socioeconomical conditions, failed to show major differences between the two groups in the global neuropsychological performance and cognitive levels. However, minor but significant differences were noted in the information vocabulary and coding subtests, at least in children aged 8. Although familial cultural influences might play a role, it would appear that some marginal impairment, with particular regard to motor-perceptual functions, be present in areas of moderate iodine deficiency.

RECIPROCAL CHANGES OF SERUM THYROGLOBULIN AND TSH IN RESIDENTS OF A MODERATE ENDEMIC GOITRE AREA

Subjects living in iodine deficient areas were reported to have elevated serum thyroglobulin (Tg) concentrations. This finding was interpreted as related to thyroid stimulation. Discrepant results, however, were found when serum Tg concentrations were correlated either with serum TSH or with goitre size. In this study we investigated the relationships between goitre size, serum Tg and serum TSH in 488 unselected adult subjects living in an endemic area of North‐Western Tuscany (Garfagnana district). The control group comprised 352 subjects residing in a non‐endemic area. In the endemic area a high prevalence of goitre was found (80·1%), thyroid enlargement being slight to moderate in the majority of cases and very large only in six subjects. Serum Tg concentrations increased and serum TSH levels decreased with the size of goitre. Statistical analysis by the chi‐square cross correlation test showed that the converse changes of serum Tg and serum TSH in relation to goitre size were highly significant. These findings indicate that the increase of serum Tg occurring in endemic goitrous subjects may be related to factors other than TSH stimulation. Functional autonomy of the thyroid may account for the finding of low serum TSH and elevated serum Tg values in patients with large goitres. The present data do not exclude the possibility that the release of Tg is influenced by TSH stimulation, but indicate that other factors may be responsible for the increased levels of Tg found in endemic goitre.

IS HUMORAL THYROID AUTOIMMUNITY RELEVANT IN AMIODARONE IODINE-INDUCED THYROTOXICOSTS (AIIT)?

Amiodarone, an iodine containing drug, may induce thyrotoxicosis by an uncertain mechanism. In this study the role of thyroid autoimmunity was evaluated in 28 consecutive patients referred to us because they had become hyperthyroid during long‐term amiodarone administration. Titres of thyroglobulin and thyroid microsomal antibodies, TSH binding‐inhibitory and thyroid stimulating antibodies were evaluated. Underlying thyroid disorders were demonstrated in 20 patients (9 of them had toxic diffuse goitre, seven toxic multinodular goitre and four toxic adenoma), while eight patients did not show any apparent thyroid gland abnormality. Circulating thyroid autoantibodies could be found in all amiodarone iodine‐induced hyperthyroid patients with toxic diffuse goitre and in one with toxic multinodular goitre, whilst they were absent in the other patients. These studies suggest that thyroid autoimmunity has little if any role in the development of thyrotoxicosis in amiodarone treated patients without underlying thyroid disorders. Furthermore, in amiodarone‐iodine‐induced thyrotoxicosis associated with various thyroid diseases, the humoral markers of thyroid autoimmunity show an incidence similar to that observed in spontaneous hyperthyroidism.

Role of autoimmune and familial factors in goiter prevalence. Studies performed in a moderately endemic area.

The goitrogenic role of autoimmune phenomena in endemic goiter is still uncertain. Scanty and discrepant results have been reported in different areas of the world. This prompted us to evaluate the prevalence of circulating thyroid antibodies in an area of North-Western Tuscany during a survey for endemic goiter. The survey was carried out according to the P.A.H.O. criteria in a stable community. In all schoolchildren (n = 142, age range 7–15 yr) and in most of their parents (n = 159), thyroid size was evaluated and urine was collected for iodine determination. Blood was drawn for determination of circulating thyroid microsomal (MAb) and thyroglobulin antibodies (TgAb), TT3, TT4 and TSH. Prevalence of goiter in schoolchildren was 77.9% and 94.8% in their parents. Mean (± S.D) urinary iodine excretion was 55.0 ± 2.1 μg/24h. The overall frequency of TgAb and MAb in the adult population was 14.4%, statistically higher than that of control subjects matched for sex and age. The frequency in schoolchildren was 4.3%. The presence of goiter in children was unrelated to the presence of thyroid antibodies in parents, whether goitrous or nongoitrous. A higher prevalence of goiter was found in children with goitrous parents as compared to children with nongoitrous parents (p < 0.005). In conclusion, the frequency of thyroid autoantibodies in the adult population of the endemic area studied was increased, but showed no relation with the presence of goiter. The prevalence of goiter in children was associated with the presence of goiter but not of thyroid autoantibodies in parents. These data suggest that autoimmune phenomena are of limited importance in the development of endemic goiter.

Detection and characterization of autoantibodies blocking the TSH-dependent cAMP production using FRTL-5 cells

Autoantibodies blocking the TSH-stimulated cAMP production (TBkAb) were measured in immunoglobulin G (IgG) preparations from 38 patients with primary autoimmune hypothyroidism, using FRTL-5 cells. TBkAb were detectable in 15/23 IgG preparations from patients with untreated idiopathic myxedema, and in 2/15 IgGs from patients under L-thyroxine treatment. None of the IgG from 22 normal subjects or from 10 patients with nonautoimmune hypothyroidism following total thyroidectomy caused any significant effect on the TSH-stimulated cAMP production. No correlation was found between TBkAb and the thyroid microsomal antibody. Antibodies inhibiting the 125I-TSH binding to TSH receptor were detectable in only 3/20 patients; IgGs from these 3 patients were also positive in the TBkAb assay. One IgG with potent TBkAb activity inhibited the TSH-stimulated adenylate cyclase in a competitive manner, while it had no effect on the forskolin-stimulated cAMP production. The inhibiting action of this IgG was almost completely lost after preabsorption with human thyroid membranes. In conclusion, we describe a new practical and sensitive method for the measurement of TBkAb; TBkAb are distinct from the microsomal antibody, and are probably directed to the TSH receptor.

Radio-receptor assay of TSH: its use to detect thyroid-stimulating immunoglobulins.

Immunoglobulins (IgG) in sera of patients with autoimmune thyroid diseases have been characterized by their ability to bind to thyroid TSH receptor sites. Thyroid membranes were prepared in hypotonic medium and discontinuous sucrose gradient flotation. 125l labelled-bovineTSH bound to the membranes at 0C for 120 min. Binding was linear with membrane concentration. Specific binding was maximum at pH 6.5, but binding studies with IgG were conducted at pH 7.5 in order to keep IgG soluble. Progressive inhibition of binding of label occurred at TSH concentration of 20 ng–50μg/ml, with half displacement at 7–70μg/ml. Unfractionated sera caused nonspecific depression of response. IgG was purified by DEAE-Sephadex absorption and used in concentration of 1.2 mg/ml or 175 μg/tube. Compared to the effect of a normal control pooled IgG on binding (“100%”), IgG from 17 normal subjects averaged 99±9% (range: 120–82%), and from 12 patients with thyroid cancer, 96±11%, both showing no inhibition of 125I-TSH binding. IgG from 15 patients with untreated Graves’ disease significantly (p<0.05) inhibited binding (81±17% of control) with up to 60% displacement of TSH. 53% of the patients were more than 2 SD below the mean normal value. Binding with IgG from sera of 8 patients with Hashimoto’s disease ranged from 61% to 120% of control. IgG from most patients with Graves’ disease compete with TSH for binding to thyroid cell membranes, and thus behave as antibodies to TSH receptors. Some patients with clinical thyroiditis have similar responses, confirming the hypothesis of a common immunologic background in these two diseases.

Evaluation of L-thyroxine replacement therapy in children with congenital hypothyroidism

The outcome of L-thyroxine (L-T4) replacement therapy in children with congenital hypothyroidism (CH) remains to be completely evaluated. In this paper the overall pattern of response to L-T4 replacement therapy was studied in a group of 19 children with CH diagnosed by neonatal screening (10 with hypoplastic/aplastic thyroid disease, group H/A; 9 with gland ectopy, group E) who were followed-up for 60 ± 27 months (mean ± SD). With 1 exception serum T4 at diagnosis was > 2 µg/dl in children of group E and < 2 µg/dl in those of group H/A. The initial dose of L-T4 (8–10 µg/kg BW/day) was modified in relation to age and weight in order to maintain serum TSH ≼ 5 µU/ml and FT3 in the normal range. A general inverse correlation between serum TSH and FT4 or FT3 concentrations was found, and the mean levels of serum FT4 and FT3 were significantly higher according to the following order of TSH results: low TSH (0–0.5 µU/ml) > normal (>0.5–5 µU/ml) > elevated TSH (>5 µU/ml). TSH levels < 5 µU/ml were associated with FT4 values in the upper half of the normal range (54% of observations) or even higher (46%). Elevation of serum FT4 alone with FT3 values in the normal range did not result in clinical thyrotoxicosis, alteration of growth or premature craniosynostosis. Mean L-T4 doses (µg/kg BW/day) administered to CH children were: 7.0 ± 1.6 between 1 and 6 months; 5.2 ± 0.9 between 6 and 12 months; 4.0 ± 0.6 between 1 e 5 yr; 3.4 ± 0.6 over 6 yr. In general, the mean L-T4 closes given to children showing low, normal or elevated TSH were widely overlaped. Growth in weight and height was normal, no significant difference being observed in children of group H/A vs. those of group E. Mental development was within the normal range, but at age 12 months children in group H/A had significantly lower DQ scores than those in group E, and at age 3 yr both groups of CH children had significantly lower IQ scores than unaffected controls. In conclusion: i) in children with CH serum TSH can be suppressed to normal or even subnormal concentrations provided that enough L-T4 is given to maintain FT4 in the upper half of the normal range or slightly higher; ii) sporadic elevations of TSH during treatment could be attributed to: failure to reassess the dose of L-T4 following the infant’s rapid gain in weight, lack of compliance, malabsorption of the drug, misunderstanding of prescription; iii) neuropsychological development was within the normal range of tests; however, the absence of functioning thyroid tissue, as shown by low T4 at diagnosis and by negative radioisotope imaging, was a risk factor for lower mental scores.

Measurement of TSAb directly in serum using FRTL-5 cells

FRTL-5 cells were shown to be suitable for the measurement of thyroid stimulating antibody (TSAb) present in sera of patients with Graves’ disease. Current methods for the assay of TSAb require the separation of immunoglobulin G (IgG)from patient sera. In this report the possibility to measure TSAb directly on serum was evaluated using FRTL-5 cells. To this purpose cells were seeded in 96-well plates and cultured for 4 days in medium deprived of TSH. Using this system bovine TSH was able to produce a significant stimulation of cAMP production at 1 μU/ml. Whole normal serum completely inhibited the stimulation of TSH as well as that of TSAb, while diluted serum was devoid of any effect. Heat inactivated sera and IgGs, prepared by DEAE Sephadex separation, were diluted in hypotonic medium and incubated with cells for 1 h at 37 C. After incubation cAMP was measured in the assay medium by RIA. In some experiments the effects of graded dilutions of sera and IgGs with known TSAb activity were compared. Sera as well as IgGs increased the cAMP production, but, at the highest concentrations, an inhibitory effect was evident. For this reason sera were tested after appropriate dilution. Thirteen/27 (48%) sera and 22/27 (81%) IgGs from patients with Graves’ disease were TSAb positive. The effect of Graves’ sera on adenylate cyclase stimulation was completely inhibited by an anti-human IgG. The results of stimulation produced by Graves’ sera and IgGs were highly correlated (r = 0.97, p < 0.001 ). In conclusion it is possible to measure TSAb directly in serum using FRTL-5 cells. This assay is less sensitive then the assay that employs the purified IgG. However, positive results were found in almost 50% of unselected Graves’ patients. Thus, it is reasonable to propose this assay as a first-line screening for TSAb; the assay employing purified IgGs can be limited to negative sera.