The Accomplishments and Legacy of Saul Hertz, MD.

The early history of the use of radioactive iodine (RAI) is complicated and interesting, and also difficult to discover, especially since several histories have presented inaccurate content. This article is a comprehensive review of the accomplishments of Saul Hertz. Extensive use of primary-source verification has clarified several issues, including the question of whether Hertz alone conceived and asked the pivotal question: "Could iodine be made radioactive artificially?"; on what date RAI was first used to treat hyperthyroidism; and why 2 articles on the first use of RAI for treatment of hyperthyroidism, from 2 different sets of authors from the same department of the same institution, appeared adjacent to each other in the same issue of the Journal of the American Medical Association in 1946. Our review also chronicles several major challenges that Hertz overcame to produce his pivotal work. Hertz was clearly the originator and a visionary of RAI therapy in benign and malignant thyroid disease. We believe he can be considered one of the fathers of nuclear medicine. Hertz's paradigm-changing work was a pivotal medical discovery of the 20th century. The legacy of Hertz continues while the application of RAI therapy continues to evolve. RAI therapy remains the preferred treatment in most situations for autonomous nodules and toxic multinodular goiter and remains a safe and effective treatment for Graves disease after more than 80 y of global clinical use. RAI treatment of differentiated thyroid cancer remains a first-line treatment for most patients after surgery, especially for those with intermediate- or high-risk disease.

Iodine-131 intervention in hyperthyroidism with hepatic insufficiency: Metabolomic evaluation.

Hyperthyroidism, often accompanied by hepatic insufficiency (HI), poses significant clinical challenges, highlighting the necessity for identifying optimal treatment strategies and early diagnostic biomarkers to improve patient outcomes. This study aimed to determine the optimal iodine-131 (131I) intervention dose for alleviating hyperthyroidism with HI and to identify serum metabolic biomarkers for early diagnosis using UPLC-Q/TOF-MS technology. A mouse model for early 131I intervention was established to monitor changes in physiological response, body weight, fur condition, thyroid, and liver function. Metabolite identification was achieved through UPLC-Q/TOF-MS and further analyzed via MetaboAnalyst. Six biomarkers were identified and subjected to ROC analysis. Early intervention with 80 µCi 131I per gram of thyroid tissue effectively controlled hyperthyroidism and improved liver function. Metabolomics analysis uncovered 63 differentially abundant metabolites, six of which (L-kynurenine, Taurochenodesoxycholic acid, Glycocholic acid, Phytosphingosine, Tryptamine, and Betaine) were identified as early warning biomarkers. Post-intervention, these biomarkers progressively returned to normal levels. This study demonstrates the efficacy of UPLC-Q/TOF-MS in identifying metabolic biomarkers for early diagnosis of hyperthyroidism with HI and highlights the therapeutic potential of early 131I intervention in normalizing these biomarkers.

Factors predicting remission in hyperthyroid patients after low-dose I-131 therapy: 20 years retrospective study from a tertiary care hospital.

OBJECTIVE: To assess the therapeutic outcome and factors predicting remission in hyperthyroid patients treated with low-dose I-131 (radioactive iodine) from a tertiary care hospital in South India. METHODS: This 20-year single-institutional retrospective study was carried out on 3891 hyperthyroid adult patients. Only those patients with complete clinical records were audited. Selection criteria were based on patients with scintigraphic diagnosis of either Graves' disease (GD), toxic multinodular goitre (TMNG) or autonomous toxic nodule (ATN) and the records of those who received low-dose I-131 therapy (LDT) between March 2000 and 2020 at Amrita Institute, Cochin were analysed. SPSS 10 software was used for statistical analysis. RESULTS: The records of 3891 hyperthyroid predominantly female patients were analysed. 65% patients had GD, 33% had TMNG and 3% were ATN. High rates of remission as early as 12 weeks (in 61% patients) was observed with a single dose of LDT while on strict iodine-free diet for 3-4 weeks prior to LDT. Study reveals that those with lower free T4 (fT4), small goitre (thyroid volume < 25 cm3), < 15% thyroid trapping function, shorter time duration from onset of hyperthyroidism to LDT, and treatment-naïve patients were factors determining high remission rates. Mann Whitney U test and Chi-square test was used to correlate variables in the remission and relapse groups. We found a positive correlation between fT4, thyroid volume (r = 0.35, p < 0.01) and trapping function (r = 0.34, p < 0.01), which were independent of age, sex, body mass index and TSH levels in our study. CONCLUSION: High therapeutic outcome was observed with a single dose of LDT while on iodine-free diet. Remission with single dose of LDT occurred in 90% patients by 5th month. Of them 56% patients were treatment naive prior to LDT. LDT is thus a safe and effective therapy in hyperthyroid patients and can be recommended as a primary modality of management.

Radioactive iodine treatment for Graves' hyperthyroidism: incidence of Graves orbitopathy.

PURPOSE: There are limited recent data on the effect of radioactive iodine (RAI) for Graves' disease on Graves' orbitopathy (GO) development or reactivation. This audit investigates the GO incidence in patients with Graves' disease after RAI treatment, and explores risk factors present, and steroid prophylaxis use. METHODS: A retrospective audit of Graves' disease patients treated with RAI over a 5-year period. Data collected: smoking status, thyroid-stimulating hormone receptor antibody (TRAb) status, GO history, Graves' disease duration, eye features pre- and post-treatment, prophylactic corticosteroids, RAI dose given, post-RAI thyroid status, duration until hypothyroid. RESULTS: One hundred one patients were included, with a median Graves' disease duration 36 months. 34/101 (33.7%) were active/ex-smokers, 86/101 (85.1%) were TRAb-positive, 11/101 (10.9%) had a GO history; 32 (31.7%) had eye features present. Median RAI dose given was 596MBq. 8/101 (7.9%) patients received prophylactic corticosteroid; 89/101 (88.1%) achieved hypothyroid state in the year after RAI. GO developed in 5/101 (5.0%), of which 4/5 (80%) were de novo in high-risk individuals who did not receive steroids. One was a GO reactivation despite steroids. Two required intravenous steroids with/without orbital radiotherapy, one completed oral steroid taper; the remainder were treated conservatively. CONCLUSION: Our cohort had a lower GO incidence in patients with Graves' disease receiving RAI, with majority arising de novo . It is essential that all patients are assessed for Graves orbitopathy risk factors and counselled adequately prior to RAI. The decision to initiate steroids should be undertaken in a multi-disciplinary setting involving endocrinologists and ophthalmologists.

Urine concentrating ability in cats with hyperthyroidism: Influence of radioiodine treatment, masked azotemia, and iatrogenic hypothyroidism.

BACKGROUND: Hyperthyroid cats often have urine specific gravity (USG) values <1.035. It remains unclear how USG changes after treatment, if USG can be used to predict azotemia after treatment, or how iatrogenic hypothyroidism influences USG values. OBJECTIVES: To determine the proportion of hyperthyroid cats with USG <1.035 vs ≥1.035; if USG changes after treatment; and whether USG <1.035 correlated with unmasking of azotemia or hypothyroidism. ANIMALS: Six hundred fifty-five hyperthyroid cats treated with radioiodine; 190 clinically normal cats. METHODS: Prospective, before-and-after study. Hyperthyroid cats had serum thyroxine, thyroid-stimulating hormone, and creatinine concentrations, and USG measured before and 6 months after successful treatment with radioiodine. RESULTS: Of untreated hyperthyroid cats, USG was ≥1.035 in 346 (52.8%) and <1.035 in 309 (47.2%). After treatment, 279/346 (80.6%) maintained USG ≥1.035, whereas 67/346 (19.4%) became <1.035; 272/309 (88%) maintained USG <1.035, whereas 37/309 (12%) became ≥1.035. Only 22/346 (6.4%) with USG ≥1.035 developed azotemia after treatment, compared with 136/309 (44%) with <1.035 (P < .001). Of cats remaining nonazotemic, 38% had USG <1.035, compared with 20% of normal cats (P < .001). The 137 cats with iatrogenic hypothyroidism had lower USG after treatment than did 508 euthyroid cats (1.024 vs 1.035), but USGs did not change after levothyroxine supplementation. USG <1.035 had high sensitivity (86.1%) but moderate specificity (65.2%) in predicting azotemia after treatment. CONCLUSIONS AND CLINICAL IMPORTANCE: Hyperthyroidism appears not to affect USG in cats. However, cats with evidence of sub-optimal concentrating ability before radioiodine treatment (USG < 1.035) are more likely to develop azotemia and unmask previously occult chronic kidney disease. Iatrogenic hypothyroidism itself did not appear to affect USG values.

Thyroid volume is the key predictor of hyperthyroidism remission after radioactive iodine therapy in pediatric patients.

Graves' disease (GD) is the leading cause of hyperthyroidism in pediatric patients. Radioactive iodine therapy (RAIT) is widely used to treat GD. However, it is still unclear exactly what determines the efficacy of RAIT in childhood and adolescence. The objective of our study was to reveal the most significant predictors of the efficacy of RAIT in pediatric GD patients. A single-center prospective observational exploratory study enrolled 144 pediatric patients (124 females and 20 males) between 8 and 18 years of age who underwent dosimetry-guided RAIT for GD for the first time. The estimated parameters included sex, age, thyroid volume, thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone receptor antibodies (TRABs) at baseline and 12 months after RAIT, 10- to 20-min 99mTc thyroid uptake (%), maximum thyroid 131I uptake (%), specific 131I uptake (MBq/g), and therapeutic activity of 131I (MBq), which was limited to 1100 MBq. The Fisher's exact test, Mann-Whitney U-test, Wilcoxon signed-rank test, ROC analysis, and the Youden index were used for statistical analysis. Twelve months after RAIT, 119 patients (83%) successfully achieved remission, 6 patients (4%) had euthyroidism, and hyperthyroidism persisted in 19 patients (13%). Thyroid volume decreased from 17.6 [14.6; 24.1] to 9.3 [7.6; 13.3] mL 12 months after the treatment (p < 0.001). The main predictor that showed a statistically significant difference between the groups of patients who achieved and did not achieve remission of GD hyperthyroidism after RAIT was the initial thyroid volume. Using the Youden index, the optimal cut-off point for the initial thyroid volume at 45.4 mL was determined.     Conclusion: The dosimetry-guided RAIT in pediatric GD patients was 83% effective at 12 months after the treatment, and the initial thyroid volume of less than 45.4 mL was the most important predictor of RAIT success. Other predictors identified in our work included FT4 levels, TRABs levels, 99mTc-pertechnetate uptake, and specific 131I uptake. What is Known: •Radioiodine therapy is a common, effective, and safe treatment for pediatric patients with Graves' disease. What is New: •The initial thyroid volume in pediatric GD patients is an important predictor of achieving hypothyroidism following radioiodine therapy. If the thyroid volume is less than 45.4 ml, radioiodine therapy limited to 1100 MBq will be effective definitive treatment.

Effect tracking of 131I treatment in Graves' hyperthyroidism patients within 1 year and analysis of the factors that may influence the cure.

OBJECTIVE: To observe the disease development and outcome of Graves' disease (GD) patients within 1 year after iodine-131 (131I) treatment, and analyze the factors affecting the treatment effect. SUBJECTS AND METHODS: Clinical data of 221 patients who received the first treatment with 131I in our department from June 2016 to October 2018 were retrospectively analyzed and they were followed up at 3 months, 6 months and 1 year after the treatment. According to the three follow-up records, the cure rate was calculated and the follow-up chart was drawn. The factors that may affect the clinical cure were analyzed according to the follow-up results after 1 year: Independent risk factors affecting the prognosis were screened out by Logistic regression analysis, and the effects of the above factors on the prognosis were further analyzed by Chi-square test, and the cure multiple relationship caused by the influencing factors was analyzed by Logistic regression analysis. RESULTS: The cure rate was 58.82% and the effective rate was 71.95%. At the 3-month follow-up, 11 patients (4.98%) presented complete response, 99 patients (44.80%) presented hypothyroidism, 93 patients (42.08%) presented partial response, and 18 patients (8.14%) presented no effect or recurrence. At 6 months, 18 cases (8.14%) had complete response, 90 cases (40.72%) had hypothyroidism, 59 cases (26.70%) had partial response, and 54 cases (24.43%) had no effect or recurrence. At 12 months, 36 cases (16.29%) had complete response, 94 cases (42.53%) had hypothyroidism, 29 cases (13.12%) had partial response, and 62 cases (28.05%) had no effect or recurrence. Thyroid weight and thyroid peroxidase antibody (TPOAb) were the influencing factors. Among all patients, patients with thyroid weight ≤28.70g were 4.25 times more likely to achieve clinical cure than patients with >28.70g [OR (95%CI):4.252 (2.383-7.588), P<0.01)], female patients with the thyroid weight ≤28.70g was 5.78 times than those with >28.70g [OR (95%CI): 5.776 (2.951-11.308), P<0.01]. In male, patients with TPOAb≤449.00IU/mL were 0.27 times more likely to achieve clinical cure than those with >449.00IU/mL [OR (95%CI): 0.274 (0.081-0.919), P<0.05]. CONCLUSION: Iodine-131 was an effective treatment to GD. Thyroid weight before treatment was the influencing factor for all patients and female patients, while TPOAb was the influencing factor for male patients.

Changes in symmetric dimethylarginine and glomerular filtration rates in hyperthyroid cats undergoing radioiodine therapy.

OBJECTIVES: The aims of this study were to evaluate concentrations of symmetric dimethylarginine (SDMA) in hyperthyroid cats before and after radioiodine treatment, and to compare results with other variables used to assess kidney function in cats (creatinine, urine specific gravity [USG] and glomerular filtration rate [GFR] measured by renal scintigraphy). METHODS: Thirteen cats diagnosed with hyperthyroidism based on clinical signs and increased serum total thyroxine (TT4) were included in this prospective study. Study design included physical examination, complete blood count, serum chemistry, TT4, urinalysis and SDMA before treatment (T0) and at 1 month (T1) and 3 months post-treatment (T3). GFR was quantified by renal scintigraphy at T0 and T3. RESULTS: Median GFR decreased significantly from baseline (3.18 ml/kg/min; range 1.35-4.87) at T3 (2.22 ml/kg/min; range 1.81-3.42 [P = 0.005]). While median creatinine and serum urea nitrogen increased post-treatment (creatinine: T0 = 0.8 mg/dl [range 0.4-1.1], T1 = 1.3 mg/dl [range 0.9-2]; T3 = 1.65 mg/dl [range 0.8-2.8]; P <0.001; serum urea nitrogen: T0 = 23 mg/dl [range 15-26]; T1 = 27 mg/dl [range 20-40]; T3 = 27.5 mg/dl [range 20-36]; P <0.001), SDMA and USG did not change significantly (SDMA: T0 = 11 µg/dl [range 7-15]; T1 = 12 µg/dl [range 6-16]; T3 = 10.5 µg/dl [range 8-21]; P = 0.789; USG: T0 = 1.030 [range 1.011-1.059]; T1 = 1.035 [range 1.012-1.044]; T3 = 1.030 [range 1.007-1.055]; P = 0.792). CONCLUSIONS AND RELEVANCE: Our data suggest that factors other than GFR may affect serum SDMA in hyperthyroid cats and that SDMA does not offer an advantage over other biomarkers traditionally used to predict changes in renal function following radioiodine therapy.

Radioiodine treatment in hyperthyroid cats: insights into the characteristics of owners and their cats, and owner motivation and perceptions.

OBJECTIVES: Radioiodine (131I) therapy is the most appropriate treatment option for many hyperthyroid cats, as it is minimally invasive and often curative. Nevertheless, 131I treatment is not always pursued by owners. Hence, it is important to obtain more insight into owner satisfaction during and after 131I treatment, and their decision-making process. In this study, we describe the characteristics of owners and their hyperthyroid cats referred for 131I therapy, and determine owners' motivation and how they experienced the 131I treatment of their cat. METHODS: A survey was sent to owners whose cats underwent 131I therapy (n = 1071) between 2010 and 2017 at Ghent University. The survey contained 35 questions with tick-box or free-text answer options concerning family situation, pet insurance, previous therapy, comorbidities, motivation for 131I therapy and owner perception of this treatment. RESULTS: In total, 438 owners completed 94% or more of the questionnaire. Over half of the cats (55%) had received previous medical, dietary or surgical treatment. Motivations for changing the initial therapy to 131I therapy included difficulties in administering medication (31%), insufficient improvement in clinical signs (23%), side effects (16%) and following the referring veterinarian's advice (16%). Almost a fifth of owners (18%) were not informed about the existence of 131I therapy by their veterinarian and found information on 131I treatment online or through friends. Hospitalising their cat was very distressing for 17% of owners. Most owners (92%) were satisfied with the treatment. Reasons for dissatisfaction were insufficient communication, iatrogenic hypothyroidism, persistent hyperthyroidism and comorbidities post-treatment. CONCLUSIONS AND RELEVANCE: Our study stresses the importance of communication regarding the possible outcome of 131I treatment, the importance of managing underlying comorbidities before treatment and anticipating the stress of owners during their cat's hospitalisation period. The results of this study could help in improving client communication when advising on 131I treatment.

Possibility analysis of thyroid imaging parameters for dose adjustment in 131I treatment of hyperthyroidism.

BACKGROUND: To determine the thyroid uptake rate by correcting the background and analyze its clinical significance. METHODS: The study included 161 patients with hyperthyroidism. The thyroid uptake rate was calculated by drawing a 100 pixels ROI (region of interest) background, above and below the thyroid and correcting the thyroid ROI for background counting. At the same time, the clinical baseline characteristic parameters such as age and thyroid volume etc. of patients with hyperthyroidism were collected. The consistency of 99mTcO4uptake rate before treatment and 131I-uptake rate after treatment, and the correlation between uptake rate of thyroid and baseline characteristic parameters were also analyzed. RESULTS: The uptake rate of 99mTcO4 was found positively correlated with 3 h-radioactive iodine uptake (RAIU), 24 h-RAIU, 3 h/24 h conversion rate, thyroid volume, 131I activity free triiodothyronine (FT3) and free thyroxine (FT4), and showed negative correlation with age, effective half-life (P<0.05). The uptake rate of 131I was found positively correlated with 3 h-RAIU, 24 h-RAIU, 3 h/24 h conversion rate, thyroid volume, 131I activity, FT3, FT4 (P<0.05). In patients with positive thyrotrophin receptor antibody (TRAb), a significant positive correlation between uptake rate of 99mTcO4 and 131I (P<0.05) was observed. There was a high consistency between pretreatment uptake rate of 99mTcO4 and post-treatment uptake rate of 131I (P=0.009; W=0.7). CONCLUSIONS: The corrected thyroid uptake rate is remarkably correlated with clinical characteristic parameters of patients, which can be used to comprehensively evaluate the comprehensive condition of patients with hyperthyroidism.

One institutions' experience with a true standard 15 mCi dose of I-131 for the treatment of Graves' disease.

INTRODUCTION: Currently, there is a lack of consensus on the fixed dosage of RAI to be administered for this purpose between the main guideline frameworks set forth by the American Thyroid Association (ATA), Society of Nuclear Medicine and Molecular Imaging (SNMMI), European Association of Nuclear Medicine (EANM) and the European Thyroid Association (ETA). In this retrospective study, we will investigate the effectiveness of using a standard dose of 15 mCi ±10% of RAI in the treatment of Graves'. METHODS: A retrospective chart review was conducted for the period between 1 May 2014 and 2 September 2020, to identify patients diagnosed with hyperthyroidism due to Graves' disease. The patients were grouped based on outcome and assessed for the efficacy of the dosage of 15 mCi ±10% of RAI in a successful treatment. RESULTS: Sixty-seven patients were identified that met the inclusion criteria between 1 May 2014 and 2 September 2020. Of the 67 RAI ablations; 60 patients became hypothyroid [60/67, (89.55%)], 2 euthyroid [2/67, (2.99%)] and 5 remained hyperthyroid [5/67, (7.46%)]. CONCLUSIONS: For the treatment of Graves' disease, the use of a standard low dose of 15 mCi ±10% has a high success rate without additional measurements or calculations beyond a standard planar image and 24-h uptake %. The adoption of a standard low dose of 15 mCi of I-131 across institutional guidelines would streamline dosage questions and eliminate the need to determine the weight of the thyroid for calculations in all RAI treatments for hyperthyroidism caused by Graves' disease.

Efficacy and Safety of Long-Term Methimazole versus Radioactive Iodine in the Treatment of Toxic Multinodular Goiter.

BACKGRUOUND: This study compared the degree of sustained control of hyperthyroidism in patients with toxic multinodular goiter (TMNG) treated with long-term methimazole (LT-MMI) or radioactive iodine (RAI). METHODS: In this clinical trial, 130 untreated patients with TMNG were randomized to either LT-MMI or RAI treatment. Both groups were followed for 108 to 148 months, with median follow-up durations of 120 and 132 months in the LT-MMI and RAI groups, respectively. Both groups of patients were followed every 1 to 3 months in the first year and every 6 months thereafter. RESULTS: After excluding patients in whom the treatment modality was changed and those who were lost to follow-up, 53 patients in the LT-MMI group and 54 in the RAI group completed the study. At the end of the study period, 50 (96%) and 25 (46%) patients were euthyroid, and two (4%) and 25 (46%) were hypothyroid in LT-MMI and RAI groups, respectively. In the RAI group, four (8%) patients had subclinical hyperthyroidism. The mean time to euthyroidism was 4.3±1.3 months in LT-MMI patients and 16.3± 15.0 months in RAI recipients (P<0.001). Patients treated with LT-MMI spent 95.8%±5.9% of the 12-year study period in a euthyroid state, whereas this proportion was 72.4%±14.8% in the RAI-treated patients (P<0.001). No major treatment-related adverse events were observed in either group. CONCLUSION: In patients with TMNG, LT-MMI therapy is superior to RAI treatment, as shown by the earlier achievement of euthyroidism and the longer duration of sustained normal serum thyrotropin.

Effect of radioiodine treatment on muscle mass in hyperthyroid cats.

BACKGROUND: Approximately 75% of hyperthyroid cats lose muscle mass as accessed with a muscle condition scoring (MCS) system. After treatment, MCS improves as the cats regain muscle mass. OBJECTIVES: To quantify the degree of muscle loss in hyperthyroid cats using ultrasonography and evaluate changes in muscle mass after treatment. ANIMALS: Forty-eight clinically normal cats and 120 cats with untreated hyperthyroidism, 75 of which were reevaluated after radioiodine-131 therapy. METHODS: Prospective cross-sectional and before-after studies. All cats underwent ultrasonography and measurement of epaxial muscle height (EMH), with subsequent calculation of vertebral and forelimb epaxial muscle scores (VEMS and FLEMS). A subset of hyperthyroid cats underwent repeat muscle imaging 6 months after treatment. RESULTS: Untreated hyperthyroid cats had a lower EMH than did clinically normal cats (median [25th-75th percentile], 0.98 [0.88-1.16] cm vs 1.34 [1.23-1.58] cm, P < .001). Seventy-seven (64.2%) untreated cats had subnormal EMH. Similarly, compared to normal cats, hyperthyroid cats had lower VEMS (0.93 [0.84-1.07] vs 1.27 [1.18-1.39], P < .001) and FLEMS (1.24 [1.10-1.35] vs 1.49 [1.39-1.63], P < .001). After treatment, EMH increased (1.03 [0.89-1.03] cm to 1.33 [1.17-1.41] cm, P < .001), with abnormally low EMH normalizing in 36/41 (88%). Both VEMS (0.94 [0.87-1.10] to 1.21 [1.10-1.31], P < .001) and FLEMS (1.31 [1.17-1.40] to 1.47 [1.38-1.66], P < .001) also increased after treatment. CONCLUSIONS AND CLINICAL IMPORTANCE: Almost two-thirds of hyperthyroid cats have abnormally low muscle mass when measured quantitatively by ultrasound. Successful treatment restores muscle mass in >85% of cats. EMH provided the best means of quantitating muscle mass in these cats.

Changes in Radiosensitivity to Gamma-Rays of Lymphocytes from Hyperthyroid Patients Treated with I-131.

This study investigated the peripheral blood lymphocytes (PBL) response to a dose of γ-rays in patients treated with radioiodine (I-131) for hyperthyroidism vs. healthy controls, to gain information about the individual lymphocytes' radio-sensitivity. Blood samples were taken from 18 patients and 10 healthy donors. Phosphorylated histone variant H2AX (γ-H2AX) and micronuclei (MN) induction were used to determine the change in PBL radio-sensitivity and the correlations between the two types of damage. The two assays showed large inter-individual variability in PBL background damage and in radio-sensitivity (patients vs. healthy donors). In particular, they showed an increased radio-sensitivity in 36% and 33% of patients, decrease in 36% and 44%, respectively. There was a scarce correlation between the two assays and no dependence on age or gender. A significant association was found between high radio-sensitivity conditions and induced hypothyroidism. PBL radio-sensitivity in the patient group was not significantly affected by treatment with I-131, whereas there were significant changes inter-individually. The association found between clinical response and PBL radio-sensitivity suggests that the latter could be used in view of the development of personalized treatments.

Time to Normalization and Sustainable Normal Serum Thyrotropin Concentrations in Patients with Hyperthyroidism: Comparison of Methimazole and Radioactive Iodine Treatments.

OBJECTIVE: The aim of this study was to compare the "time to euthyroidism" and "time spent in euthyroidism" following methimazole (MMI) and radioactive iodine (RAI) treatments. METHODS: Three hundred fifty-eight patients with hyperthyroidism, 178 who underwent long-term MMI treatment and 180 patients who underwent RAI treatment, were analyzed. The time to normalization of increased serum values of free thyroxine and triiodothyronine and suppressed serum thyroid-stimulating hormone (TSH) values as well as the percentage of time that the thyroid hormone levels remained within normal ranges during a mean follow-up time of 12 years were compared. RESULTS: The mean time to euthyroidism was 4.59 ± 2.63 months (range, 2-16 months) in the MMI group and 15.39 ± 12.11 months (range, 2-61 months) in the RAI group (P < .001). During follow-up, the percentage of time spent in euthyroidism was 94.5% ± 7.3% and 82.5% + 11.0% in the MMI and RAI groups, respectively (P < .001). Serum TSH values above and below the normal range were observed in 5.3% and 0.2% of patients, respectively, in the MMI group and 9.8% and 7.7% of patients, respectively, in the RAI group (P < .001). The time to euthyroidism and the percentage of time spent in euthyroidism in 40 RAI-treated patients with euthyroidism were similar to those in the MMI group and significantly shorter than those in the RAI-treated hypothyroid and relapsed subgroups. In patients who continued MMI therapy for >10 years, the percentage of time spent in euthyroidism was >99%. CONCLUSION: In our cohort of selected patients, MMI therapy was accompanied by faster achievement of the euthyroid state and more sustained normal serum TSH levels during long-term follow-up compared with RAI therapy.

A model to determine at-home restrictions for cats after treatment of hyperthyroidism with radioiodine.

OBJECTIVES: Felinehyperthyroidism is the most common endocrine disease of older cats and radioiodine is considered to be the gold standard treatment. Isolation periods following treatment vary depending on both individual treatment facilities and the relevant legislation of the country; therefore, there is no recognised standardised protocol defining the length of isolation. This work describes how our institution validated that its owner restrictions met dose constraints by using a model of iodine retention to calculate the required duration and nature of owner restrictions. MATERIALS AND METHODS: The retained radioactivity of cats at the point of discharge was used to simulate the radiation dose to owners in the 90 days following release. The model created was used to calculate the minimum duration of isolation for a range of administered activities and owner restrictions. RESULTS: Using the model, it was found that when injected with the maximum dose used, 222 MBq radioiodine, it was possible to release cats after 14 days of isolation and keep owner doses below 0.30 mSv (whole-body effective dose constraint for a single radiation source) with some restrictions. It was possible to release after 23 days with no restrictions. CLINICAL SIGNIFICANCE: The present study provides clinicians with a consistent and verified method in which they can calculate the isolation periods for radioiodine-treated cats.

Radioiodine treatment of hyperthyroidism in cats: results of 165 cats treated by an individualised dosing algorithm in Spain.

OBJECTIVES: Although radioiodine (131I) is the treatment of choice for feline hyperthyroidism, 131I-dosing protocols commonly induce iatrogenic hypothyroidism and expose azotaemia. A recently reported patient-specific 131I dosing algorithm minimised the risk of 131I-induced hypothyroidism and azotaemia, while maintaining high cure rates. The aim of the study was to report results of 131I treatment in a European population of hyperthyroid cats using this patient-specific dosing algorithm. METHODS: This prospective case series (before-and-after study) evaluated 165 hyperthyroid cats referred for 131I treatment. All cats had serum concentrations of thyroxine (T4), triiodothyronine (T3) and thyroid-stimulating hormone (TSH) measured (off methimazole ⩾1 week). Thyroid volume and percentage uptake of 99mTc-pertechnetate (TcTU) were determined using thyroid scintigraphy. An initial 131I dose was calculated by averaging dose scores for T4/T3 concentrations, thyroid volume and TcTU; 70% of that composite dose was then administered. Twenty-four hours later, percentage 131I uptake was measured, and additional 131I administered as needed to deliver an adequate radiation dose to the thyroid tumour(s). Serum concentrations of T4, TSH and creatinine were determined 6-12 months later. RESULTS: Median calculated 131I dose was 2.15 mCi (range 1.2-7.5), with only 51 (30.9%) receiving ⩾2.5 mCi. Of 165 cats, 124 (75.2%) became euthyroid, seven (4.2%) became overtly hypothyroid, 27 (16.4%) became subclinically hypothyroid and seven (4.2%) remained hyperthyroid. A higher proportion of overtly (85.7%) and subclinically (26.9%) hypothyroid cats developed azotaemia than euthyroid cats (13.6%; P = 0.0002). Hypothyroid cats were older (P = 0.016) and more likely to have detectable TSH concentrations (P = 0.025) and symmetrical bilateral distribution of 99mTc-pertechnetate uptake (P = 0.0002), whereas persistently hyperthyroid cats had higher severity scores (P = 0.012). CONCLUSIONS AND RELEVANCE: Our results confirm that 131I dosing with this new algorithm results in high cure rates, with a lowered prevalence of 131I-induced overt hypothyroidism and azotaemia. Age, serum TSH concentrations, bilateral, symmetrical uptake and severity score help predict outcome.